the Johann Bayer Designation

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Bayer Portrait

Johann Bayer (1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain, Lower Bavaria, in 1572. At twenty, in 1592 he began his study of philosophy and law at the University of Ingolstadt, after which he moved to Augsburg to begin work as a lawyer, becoming legal adviser to the city council in 1612.

Bayer had several interests outside his work, including archaeology and mathematics. However, he is primarily known for his work in astronomy; particularly for his work on determining the positions of objects on the celestial sphere. He remained unmarried and died in 1625.

Bayer is most famous for his star atlas Uranometria Omnium Asterismorum (“Uraniometry of all the asterisms”), which was first published in 1603 in Augsburg and dedicated to two prominent local citizens. This was the first atlas to cover the entire celestial sphere.

It was based upon the work of Tycho Brahe and may have borrowed from Alessandro Piccolomini’s 1540 star atlas, De le stelle fisse (“Of the fixed stars”), although Bayer included an additional 1,000 stars. The Uranometria introduced a new system of star designation which has become known as the Bayer designation. Bayer’s atlas added twelve new constellations to fill in the far south of the night sky, which was unknown to ancient Greece and Rome.

The crater Bayer on the Moon is named after him.

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Nebula with a slice of lemon

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The Lemon slice nebula, also known as IC 3568, is a planetary nebula that is 1.3 kiloparsecs (4500 ly) away from Earth in the constellation of Camelopardalis (just 7.5 degrees from Polaris). It is a relatively young nebula and has a core diameter of only about 0.4 light years.

The Lemon slice nebula is one of the most simple nebulae known, with an almost perfectly spherical morphology. It appears very similar to a lemon, for which it is named. The core of the nebula does not have a distinctly visible structure in formation and is mostly composed of ionized helium.

The central star is a very hot and bright asymptotic red giant, and can be seen as a red-orange hue in an amateur’s telescope. A faint halo of interstellar dust surrounds the nebula.

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Swimming with Delphinus

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Delphinus is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical Union. It is one of the smaller constellations, ranked 69th in size.

Delphinus’ brightest stars form a distinctive asterism that can easily be recognized. It is bordered (clockwise from north) by Vulpecula the fox, Sagitta the arrow, Aquila the eagle, Aquarius the water-carrier, Equuleus the foal and Pegasus the flying horse.

Delphinus does not have any bright stars; its brightest star is of magnitude 3.8. The main asterism in Delphinus is Job’s Coffin, formed from the four brightest stars: Alpha, Beta, Gamma, and Delta Delphini. Alpha and Beta Delphini are named Sualocin and Rotanev, respectively. When read backwards, they read as Nicolaus Venator, the Latinized name of Palermo Observatory‘s former director, Niccolò Cacciatore. However, Delphinus is in a rich Milky Way star field.

Alpha Delphini, called Sualocin, is a blue-white hued main sequence star of magnitude 3.8, 241 light-years from Earth. Beta Delphini, called Rotanev, is a close binary star and the brightest in Delphinus, divisible in only large amateur telescopes. To the unaided eye, it appears to be a white star of magnitude 3.6. It has a period of 27 years and is 97 light-years from Earth. Gamma Delphini is a celebrated binary star among amateur astronomers. The primary is a gold-colored star of magnitude 4.3 and the secondary is a yellow-tinged star of magnitude 5.1. 102 light-years away, the components of Gamma Delphini are divisible in a small amateur telescope. The secondary, also described as green, is 10 arcseconds from the primary. Struve 2725, called the “Ghost Double”, is a pair that appears similar to a dimmer Gamma Delphini. Its components of magnitudes 7.6 and 8.4 are separated by 6 arcseconds and are 15 arcminutes from Gamma Delphini itself.

There are several dimmer stars in Delphinus. Delta Delphini is a type A7 IIIp star of magnitude 4.43. Epsilon Delphini, called Deneb Dulfim, meaning “tail of the Dolphin”, is a star of spectral class B6 III and magnitude 4.

Delphinus is also home to several variable stars. R Delphini is a Mira-type variable star with a period of 285.5 days. Its magnitude ranges between a maximum of 7.6 and a minimum of 13.8.

Rho Aquilae moved across the border into Delphinus in 1992.

HR Delphini was a nova that brightened to magnitude 3.5 in December 1967. On 14 August 2013, a possible nova was discovered by amateur astronomer Koichi Itagaki, initially labelled PNV J20233073+2046041, now labelled Nova Delphini 2013.

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going over my oberon

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Big Moon of Uranus

Oberon, also designated Uranus IV, is the outermost major moon of the planet Uranus. It is the second-largest and second most massive of the Uranian moons, and the ninth most massive moon in the Solar System. Discovered by William Herschel in 1787, Oberon is named after the mythical king of the fairies who appears as a character in Shakespeare‘s A Midsummer Night’s Dream. Its orbit lies partially outside Uranus’s magnetosphere.

It is likely that Oberon formed from the accretion disk that surrounded Uranus just after the planet’s formation. The moon consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the boundary between the mantle and the core. The surface of Oberon, which is dark and slightly red in color, appears to have been primarily shaped by asteroid and comet impacts. It is covered by numerous impact craters reaching 210 km in diameter. Oberon possesses a system of chasmata (graben or scarps) formed during crustal extension as a result of the expansion of its interior during its early evolution.

The Uranian system has been studied up close only once: the spacecraft Voyager 2 took several images of Oberon in January 1986, allowing 40% of the moon’s surface to be mapped.

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Oberon orbits Uranus at a distance of about 584,000 km, being the farthest from the planet among its five major moons. Oberon’s orbit has a small orbital eccentricity and inclination relative to the equator of Uranus. Its orbital period is around 13.5 days, coincident with its rotational period. In other words, Oberon is a synchronous satellitetidally locked, with one face always pointing toward the planet. Oberon spends a significant part of its orbit outside the Uranian magnetosphere. As a result, its surface is directly struck by the solar wind. This is important, because the trailing hemispheres of satellites orbiting inside a magnetosphere are struck by the magnetospheric plasma, which co–rotates with the planet. This bombardment may lead to the darkening of the trailing hemispheres, which is actually observed for all Uranian moons except Oberon.

Because Uranus orbits the Sun almost on its side, and its moons orbit in the planet’s equatorial plane, they (including Oberon) are subject to an extreme seasonal cycle. Both northern and southern poles spend 42 years in a complete darkness, and another 42 years in continuous sunlight, with the sun rising close to the zenith over one of the poles at each solstice. The Voyager 2 flyby coincided with the southern hemisphere’s 1986 summer solstice, when nearly the entire northern hemisphere was in darkness. Once every 42 years, when Uranus has an equinox and its equatorial plane intersects the Earth, mutual occultations of Uranus’s moons become possible. One such event, which lasted for about six minutes, was observed on May 4, 2007, when Oberon occulted Umbriel.

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Uranus moons is nothing to do with innuendo

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Discovery and  History

Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other three ellipsoidal moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda). These five have planetary mass, and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes.

Uranian moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with the planet’s rings. The five major moons are massive enough to have achieved hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about one-twentieth the mass of the Moon. Uranus’s irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at great distances from the planet.

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Under my umbriel

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Umbriel is a moon of Uranus discovered on October 24, 1851, by William Lassell. It was discovered at the same time as Ariel and named after a character in Alexander Pope‘s poem The Rape of the Lock. Umbriel consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle. The surface is the darkest among Uranian moons, and appears to have been shaped primarily by impacts. However, the presence of canyons suggests early endogenic processes, and the moon may have undergone an early endogenically driven resurfacing event that obliterated its older surface.

Covered by numerous impact craters reaching 210 km (130 mi) in diameter, Umbriel is the second most heavily cratered satellite of Uranus after Oberon. The most prominent surface feature is a ring of bright material on the floor of Wunda crater. This moon, like all moons of Uranus, probably formed from an accretion disk that surrounded the planet just after its formation. The Uranian system has been studied up close only once, by the spacecraft Voyager 2 in January 1986. It took several images of Umbriel, which allowed mapping of about 40% of the moon’s surface.

Uranus

 

Umbriel, along with another Uranian satellite, Ariel, was discovered by William Lassell on October 24, 1851. Although William Herschel, the discoverer of Titania and Oberon, claimed at the end of the 18th century that he had observed four additional moons of Uranus, his observations were not confirmed and those four objects are now thought to be spurious.

All of Uranus’s moons are named after characters created by William Shakespeare or Alexander Pope. The names of all four satellites of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell. Umbriel is the ‘dusky melancholy sprite’ in Alexander Pope’s The Rape of the Lock, and the name suggests the Latin umbra, meaning shadow. The moon is also designated Uranus II.

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The Nebula that looks like a Garden Ant

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Mz 3 (Menzel 3) is a young bipolar planetary nebula in the constellation Norma that is composed of a bright core and four distinct high-velocity outflows that have been named lobes, columns, rays, and chakram. These nebulosities are described as: two spherical bipolar lobes, two outer large filamentary hour-glass shaped columns, two cone shaped rays, and a planar radially expanding, elliptically shaped chakram.

Image of Ant_Nebula (Mz 3)

Mz 3 is a complex system composed of three nested pairs of bipolar lobes and an equatorial ellipse. Its lobes all share the same axis of symmetry but each have very different morphologies and opening angles.

It is an unusual PN in that it is believed, by some researchers, to contain a symbiotic binary at its center. Study suggests that the dense nebular gas at its center may have originated from a source different from that of its extended lobes.

The working model to explain this hypothesizes that this PN is composed of a giant companion that caused a central dense gas region to form, and a white dwarf that provides ionizing photons for the PN.

Mz 3 is often referred to as the Ant Nebula because it resembles the head and thorax of a garden-variety ant.

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The Shape of a Nebula

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The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated with the AFCRL Infrared Sky Survey called Hi Star. The binary system at the center of the nebula was first discovered by Robert Grant Aitken in 1915.

Diffraction-limited speckle images of it in visible and near infrared light reveal a highly symmetric, compact bipolar nebula with X-shaped spikes which imply toroidal dispersion of the circumstellar material. The central binary system is completely obscured, providing no direct light.

 

Image-of-The_Red_Rectangle_around_the_star_HD_44179

 

On the 203rd Meeting of the American Astronomical Society in January 2004, information was reported by a team led by A. Witt of the University of Toledo, Ohio, that his team had discovered the spectral signatures of the polycyclic aromatic hydro carbons anthracene and pyrene in the ultraviolet light emitted by the nebula – potentially vital organic molecules for the formation of life. Until recently, it was thought that the ultraviolet light would quickly destroy these hydrocarbons; the fact that the hydrocarbons still exist today has been explained by recently discovered molecular forces.

A likely explanation for its symmetry is that the central star – actually a close pair of stars – is surrounded by a thick dust torus which pinches the otherwise spherical outflow into tip-touching cone shapes. Because we view the torus edge-on, the boundary edges of the cone shapes seem to form an X.

The distinct rungs suggest the outflow occurs in fits and starts. About 2,300 light-years away toward the constellation Monoceros, the Red Rectangle Nebula should be transformed into a planetary nebula as its cool central star becomes a hot white dwarf over the next few thousand years.

The Hubble Space Telescope has revealed a wealth of new features in the Red Rectangle that cannot be seen by ground-based telescopes looking through Earth‘s turbulent atmosphere. The origins of many of the features in this dying star still remain hidden or even outright mysterious. Some are well explained by theorists like the Dutch scientist Vincent Icke from Leiden University in the Netherlands.

In 1981 Vincent Icke and collaborators showed that a spherical gas ejection from a dying star hitting a dust torus would give rise to shocks that can produce cone-like outflows similar to the two cones seen in this nebula.

Of the many different parameters in Vincent Icke’s calculations, only the density of the gas and the dust are observed in the nebula.

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Lassell discovered Triton

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William Lassell FRS (18 June 1799 – 5 October 1880) was an English merchant and astronomer.

Born in Bolton, a town west of Manchester, and educated in Rochdale. After the death of his father, he was apprenticed from 1814 to 1821 to a merchant in Liverpool. He then made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy. He built an observatory at his house “Starfield” in West Derby, a suburb of Liverpool.

There he had a 24-inch (610 mm) reflector telescope, for which he pioneered the use of an equatorial mount for easy tracking of objects as the Earth rotates. He ground and polished the mirror himself, using equipment he constructed. The observatory was later (1854) moved further out of Liverpool, to Bradstone.

In 1846 Lassell discovered Triton, the largest moon of Neptune, just 17 days after the discovery of Neptune itself by German astronomer Johann Gottfried Galle. In 1848 he independently co-discovered Hyperion, a moon of Saturn. In 1851 he discovered Ariel and Umbriel, two moons of Uranus.

In 1855, he built a 48-inch (1,200 mm) telescope, which he installed in Malta because of the observing conditions that were better than in often overcast England. On his return to the UK after several years in Malta he moved to Maidenhead and operated his 24-inch (610 mm) telescope in an observatory there.

He won the Gold Medal of the Royal Astronomical Society in 1849, and served as its president for two years starting in 1870. He was also elected a Fellow of the Royal Society in 1849 and won their Royal Medal in 1858.

Lassell died in Maidenhead in 1880. Upon his death, he left a fortune of £80,000 (roughly equivalent to 8.8 million American dollars by today’s standards). His telescope was presented to the Royal Observatory in Greenwich.

The crater Lassell on the Moon, a crater on Mars, the asteroid 2636 Lassell and a ring of Neptune are named in his honour.

image-Portrait of Lassell

 

 

 

 

 

 

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Image of Triton Moon with Coleyartastro

 

 

 

 

Tonight I Visit Triton

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Triton is the largest moon of the planet Neptune. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the opposite direction to its planet’s rotation. At 2,700 kilometres (1,700 mi) in diameter, it is the seventh-largest moon in the Solar System.

Because of its retrograde orbit and composition similar to Pluto‘s, Triton is thought to have been captured from the Kuiper belt. Triton has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. Triton has a mean density of 2.061 grams per cubic centimetre (0.0745 lb/cu in) and is composed of approximately 15–35% water ice.

Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young, with a complex geological history revealed in intricate cryovolcanic and tectonic terrains. Part of its crust is dotted with geysers thought to erupt nitrogen. Triton has a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth’s atmosphere at sea level.

Image of Triton Moon with Coleyartastro

Triton was discovered by British astronomer William Lassell on October 10, 1846, just 17 days after the discovery of Neptune.

A brewer by trade, Lassell began making mirrors for his amateur telescope in 1820. When John Herschel received news of Neptune’s discovery, he wrote to Lassell suggesting he search for possible moons. Lassell did so and discovered Triton eight days later. Lassell also claimed to have discovered rings. Although Neptune was later confirmed to have rings, they are so faint and dark that it is doubtful that he actually saw them.

Triton is named after the Greek sea god Triton (Τρίτων), the son of Poseidon (the Greek god comparable to the Roman Neptune). The name was first proposed by Camille Flammarion in his 1880 book Astronomie Populaire, although it was not officially adopted until many decades later. Until the discovery of the second moon Nereid in 1949, Triton was commonly known as simply “the satellite of Neptune”. Lassell did not name his own discovery, although he suggested names a few years after his subsequent discovery of an eighth moon of Saturn (Hyperion).

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Triton – Neptune

Supernova Sol

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Our Nearest Star will be a Red Giant

The Sun does not have enough mass to explode as a supernova. Instead it will exit the main sequence in approximately 5.4 billion years and start to turn into a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of the solar system’s inner planets, possibly including Earth.
Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled, and the Earth will be hotter than Venus is today. Once the core hydrogen is exhausted in 5.4 billion years, the Sun will expand into a subgiant phase and slowly double in size over about half a billion years.

It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous.

This then starts the red giant branch (RGB) phase where the Sun will spend around a billion years and lose around a third of its mass.
After RGB the Sun now has only about 120 million years of active life left, but they are highly eventful. First the core ignites violently in the helium flash, and the Sun shrinks back to around 10 times its current size with 50 times the luminosity, with a temperature a little lower than today.

It has now reached the red clump or horizontal branch (HB), but a star of the Sun’s mass does not evolve blueward along the HB. Instead it just becomes mildly larger and more luminous over about 100 million years as it continues to burn helium in the core.

Mimas

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Mimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I.

With a diameter of 396 kilometres (246 mi) it is the 21st-largest moon in the Solar System and is the smallest astronomical body that is known to be rounded in shape because of self-gravitation.

Mimas was discovered by the astronomer William Herschel on 17 September 1789. He recorded his discovery as follows: “The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation.”

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Mimas the Death Star

When seen from certain angles, Mimas resembles the Death Star, a fictional space station known from the film Star Wars Episode IV: A New Hope, which is said to be roughly 140 kilometres in diameter. Herschel resembles the concave disc of the Death Star’s “superlaser”. This is coincidental, as the film was made nearly three years before Herschel was discovered.

In 2010, NASA revealed a temperature map of Mimas, using images obtained by Cassini. The warmest regions, which are along one edge of Mimas, create a shape similar to the video game character Pac-Man, with Herschel Crater assuming the role of an “edible dot” or “power pellet” known from Pac-Man gameplay.

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Supernovae Definition coleyartastro

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As part of the attempt to understand supernovae, astronomers have classified them according to their light curves and the absorption lines of different chemical elements that appear in their spectra. The first element for division is the presence or absence of a line caused by hydrogen. If a supernova’s spectrum contains lines of hydrogen (known as the Balmer series in the visual portion of the spectrum) it is classified Type II; otherwise it is Type I. In each of these two types there are subdivisions according to the presence of lines from other elements or the shape of the light curve (a graph of the supernova’s apparent magnitude as a function of time).

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Star Count

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Space velocity

The component of stellar motion toward or away from the Sun, known as radial velocity, can be measured from the spectrum shift caused by the Doppler effect. The transverse, or proper motion must be found by taking a series of positional determinations against more distant objects. Once the distance to a star is determined through astrometric means such as parallax, the space velocity can be computed. This is the star’s actual motion relative to the Sun or the local standard of rest (LSR). The latter is typically taken as a position at the Sun’s present location that is following a circular orbit around the galactic center at the mean velocity of those nearby stars with low velocity dispersion. The Sun’s motion with respect to the LSR is called the “peculiar solar motion”.

The components of space velocity in the Milky Way‘s Galactic coordinate system are usually designated U, V, and W, given in km/s, with U positive in the direction of the Galactic center, V positive in the direction of galactic rotation, and W positive in the direction of the North Galactic Pole. The peculiar motion of the Sun with respect to the LSR is (U, V, W) = (10.00 ± 0.36, 5.23 ± 0.62, 7.17 ± 0.38) km/s.

The stars in the Milky Way can be subdivided into two general populations, based on their metallicity, or proportion of elements with atomic numbers higher than helium. Among nearby stars, it has been found that population I, higher metallicity stars have generally lower velocities than older, population II stars. The latter have elliptical orbits that are inclined to the plane of the galaxy. Comparison of the kinematics of nearby stars has also led to the identification of stellar associations. These are most likely groups of stars that share a common point of origin in giant molecular clouds.

Within the Milky Way galaxy, there are three primary components of stellar kinematics: the disk, halo and bulge or bar. These kinematic groups are closely related to the stellar populations in the galaxy, forming a strong correlation between the motion and chemical composition, thus indicating different formation mechanisms. The halo may be further sub-divided into an inner and outer halo, with the inner halo having a net prograde rotation with respect to the galaxy and the outer a net retrograde movement.

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Arcturus

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Naked Eye Sky View of Arcturus

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Arcturus of the constellation Boötes is the brightest star in the northern celestial hemisphere. With a visual magnitude of −0.04, it is the fourth brightest star in the night sky, after −1.46 magnitude Sirius, −0.86 magnitude Canopus, and −0.27 magnitude Alpha Centauri. It is a relatively close star at only 36.7 light-years from Earth, and, together with Vega and Sirius, one of the most luminous stars in the Sun‘s neighborhood.

Arcturus is a type K0 III orange giant star, with an absolute magnitude of −0.30. It has likely exhausted its hydrogen from its coreand is currently in its active hydrogen shell burning phase. It will continue to expand before entering horizontal branch stage of its life cycle.

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Lagoon Nebula

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Giant interstellar cloud in the constellation Sagittarius

The Lagoon Nebula is estimated to be between 4,000-6,000 light years from the Earth. In the sky of Earth, it spans 90′ by 40′, translates to an actual dimension of 110 by 50 light
years. Like many nebulas, it appears pink in time-exposure color photos but is gray to the eye peering through binoculars or a telescope, human vision having poor color sensitivity
at low light levels. The nebula contains a number of Bok globules (dark, collapsing clouds of protostellar material), the most prominent of which have been catalogued by E. E.
Barnard as B88, B89 and B296.

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It also includes a funnel-like or tornado-like structure caused by a hot O-type star that emanates ultraviolet light, heating and ionizing gases on the surface of the nebula.

The Lagoon Nebula also contains at its centre a structure known as the Hourglass Nebula (so named by John Herschel), which should not be confused with the better known Hourglass Nebula in the constellation of Musca.

In 2006 the first four Herbig–Haro objects were detected within the Hourglass, also including HH 870. This provides the first direct evidence of active star formation by accretion within it.

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The Lagoon Nebula was discovered by Giovanni Hodierna before 1654 and is one of only two star-forming nebulae faintly visible to the naked eye from mid-northern latitudes.
Seen with binoculars, it appears as a distinct oval cloudlike patch with a definite core. In the foreground is the open cluster NGC 6530.

 

Old Massive Star Eta Carinae

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Eta Carinae formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity over five million times that of the Sun, located around 7500 light-years (2300 parsecs) distant in the direction of the constellation Carina.

Sting In The Tail of Scorpius

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Antares is the massive star

The seventeenth brightest star in the night-time sky and the brightest star in the constellation Scorpius, and is often referred to as “the heart of the scorpion”. Along with Aldebaran, Regulus, and Fomalhaut, Antares comprises the group known as the ‘Royal stars of Persia’. It is one of the four brightest stars near the ecliptic.

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Distinctly reddish when viewed with the unaided eye, Antares is a red supergiant of spectral type M0.5Iab and is one of the largest and most luminous observable stars. It is a slow irregular variable star with an average magnitude of +1.09  Antares is the brightest, most massive, and most evolved stellar member of the nearest OB association (the Scorpius-Centaurus Association). Antares is a member of the Upper Scorpius subgroup of the Scorpius-Centaurus Association, which contains thousands of stars with mean age 11 million years at a distance of approximately 145 parsecs (470 light years).

Constellation-Scorpius-Antares

Antares is a supergiant star with a stellar classification of M0.5Iab. With a radius that is approximately 883 times that of the Sun. If placed in the center of our Solar System, its outer surface would lie between the orbits of Mars and Jupiter. Based upon parallax measurements, Antares is approximately 550 light-years (170 parsecs) from the Earth. Its visual luminosity is about 10,000 times that of the Sun, but because the star radiates a considerable part of its energy in the infrared part of the spectrum, the bolometric luminosity equals roughly 65,000 times that of the Sun. The mass of the star has been calculated to be in the range of 15 to 18solar masses. A recent analysis comparing the effective temperature and luminosity of Antares to theoretical evolutionary tracks for massive stars which include rotation and mass loss yielded a mass of approximately 17 solar masses and age of 12 million years old.

The size of Antares may be calculated using its parallax and angular diameter. The parallax angle is given in the box to the right, and the angular diameter is known from lunar occultation measurements (41.3 ± 0.1 mas). This implies a radius of 755 solar radii at 170pc.

Antares is a type LC slow irregular variable star, whose apparent magnitude slowly varies from +0.88 to +1.16.

Antares is visible in the sky all night around May 31 of each year, when the star is at opposition to the Sun. At this time, Antares rises at dusk and sets at dawn as seen at the equator. For approximately two to three weeks on either side of November 30, Antares is not visible in the night sky, because it is near conjunction with the Sun; this period of invisibility is longer in the Northern Hemisphere than in the Southern Hemisphere, since the star’s declination is significantly south of the celestial equator.

Deneb the Huge Summertime Star

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Cygnus featuring Deneb

The brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars. However, its exact distance (and hence luminosity) has been difficult to calculate, so it is somewhere between 55,000 and 196,000 times as luminous as the Sun.

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Deneb lies at one vertex of a widely spaced asterism called the Summer Triangle, the other two members of which are the zero-magnitude stars Vega in the constellation Lyra and Altair in Aquila. This formation is the approximate shape of a right triangle, with Deneb located at one of the acute angles. The Summer Triangle is recognizable in the northern skies for there are few other bright stars in its vicinity.

Deneb in Cygnus

Deneb in Cygnus

Deneb is also easily spotted as the tip of the Northern Cross asterism made up of the brightest stars in Cygnus, the others being Beta (Albireo), GammaDelta, and Epsilon Cygni. It never dips below the horizon at or above 45° north latitude, just grazing the northern horizon at its lowest point at such locations as Minneapolis,Montréal and Turin.

In the northern hemisphere Deneb is high in the sky during summer evenings.

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The Mariner 5 Spacecraft

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Visiting Venus

Mariner 5 was a spacecraft of the Mariner program that carried a complement of experiments to probe Venus‘ atmosphere by radio occultation, measure the hydrogen Lyman-alpha (hard ultraviolet) spectrum, and sample the solar particles and magnetic field fluctuations above the planet. Its goals were to measure interplanetary and Venusian magnetic fields, charged particles, plasma, radio refractivity and UV emissions of the Venusian atmosphere.

Mariner 5 was actually built as a backup to Mariner 4, but after the success of the Mariner 4 mission, it was modified for the Venus mission by removing the TV camera, reversing and reducing the four solar panels, and adding extra thermal insulation.

It was launched toward Venus on June 14, 1967 from Cape Canaveral Air Force Station Launch Complex 12 and flew by the planet on October 19 that year at an altitude of 3,990 kilometers (2,480 mi). With more sensitive instruments than its predecessor Mariner 2, Mariner 5 was able to shed new light on the hot, cloud-covered planet and on conditions in interplanetary space.

Radio occultation data from Mariner 5 helped to understand the temperature and pressure data returned by the Venera 4lander, which arrived at Venus shortly before it. After these missions, it was clear that Venus had a very hot surface and an atmosphere even denser than expected.

The operations of Mariner 5 ended in November 1967 and it is now defunct in a heliocentric orbit.

Spacecraft-mariner5-NASA-image

Mariner 5

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Venus Geography

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Venus is one of the four terrestrial planets in the Solar System, meaning that, like Earth, it is a rocky body. In size and mass, it is similar to Earth, and is often described as Earth’s “sister” or “twin”. The diameter of Venus is 12,092 km (only 650 km less than Earth’s) and its mass is 81.5% of Earth’s. Conditions on the Venusian surface differ radically from those on Earth, owing to its dense carbon dioxide atmosphere. The mass of the atmosphere of Venus is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.

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The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. It was finally mapped in detail by Project Magellan in 1990–91. The ground shows evidence of extensive volcanism, and the sulfur in the atmosphere may indicate there have been some recent eruptions.

About 80% of the Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains. Two highland “continents” make up the rest of its surface area, one lying in the planet’s northern hemisphere and the other just south of the equator. The northern continent is called Ishtar Terra, after Ishtar, the Babylonian goddess of love, and is about the size of Australia. Maxwell Montes, the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km above the Venusian average surface elevation. The southern continent is called Aphrodite Terra, after the Greek goddess of love, and is the larger of the two highland regions at roughly the size of South America. A network of fractures and faults covers much of this area.

The absence of evidence of lava flow accompanying any of the visible caldera remains an enigma. The planet has few impact craters, demonstrating the surface is relatively young, approximately 300–600 million years old. In addition to the impact craters, mountains, and valleys commonly found on rocky planets, Venus has some unique surface features. Among these are flat-topped volcanic features called “farra“, which look somewhat like pancakes and range in size from 20 to 50 km across, and from 100 to 1,000 m high; radial, star-like fracture systems called “novae”; features with both radial and concentric fractures resembling spider webs, known as “arachnoids“; and “coronae”, circular rings of fractures sometimes surrounded by a depression. These features are volcanic in origin.

Most Venusian surface features are named after historical and mythological women. Exceptions are Maxwell Montes, named after James Clerk Maxwell, and highland regions Alpha RegioBeta Regio and Ovda Regio. The former three features were named before the current system was adopted by the International Astronomical Union, the body that oversees planetary nomenclature.

The longitudes of physical features on Venus are expressed relative to its prime meridian. The original prime meridian passed through the radar-bright spot at the center of the oval feature Eve, located south of Alpha Regio. After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne.

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White Light – Venus

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Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has no natural satellite. It is named after the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows. Because Venus is an inferior planet from Earth, it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°.

Venus is a terrestrial planet and is sometimes called Earth’s “sister planet” because of their similar size, mass, proximity to the Sun and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet’s surface is 92 times that of Earth’s. With a mean surface temperature of 735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar System, even though Mercury is closer to the Sun.

Venus has no carbon cycle that puts carbon into rock, nor does it seem to have any organic life to absorb carbon in biomass. Venus is shrouded by an opaque layer of highly reflective clouds of sulphuric acid, preventing its surface from being seen from space in visible light. It may have had oceans in the past, but these would have vaporized as the temperature rose due to a runaway greenhouse effect. The water has most probably photo dissociated, and, because of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind. Venus’s surface is a dry desertscape interspersed with slab-like rocks and periodically refreshed by volcanism.

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Second-Rock-From-The-Sun

Venus – Earth’s Twin?

 

Why gravitational slingshots are used

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A spacecraft traveling from Earth to an inner planet will increase speed because it is falling toward the Sun, and a spacecraft traveling from Earth to an outer planet will decrease speed because it is leaving the vicinity of the Sun.

Although the orbital speed of an inner planet is greater than that of the Earth, a spacecraft traveling to an inner planet, even at the minimum speed needed to reach it, is still accelerated by the Sun’s gravity to a speed notably greater than the orbital speed of that destination planet. If the spacecraft’s purpose is only to fly by the inner planet, then there is typically no need to slow the spacecraft. However, if the spacecraft is to be inserted into orbit about that inner planet, then there must be some way to slow the spacecraft.

Similarly, while the orbital speed of an outer planet is less than that of the Earth, a spacecraft leaving the Earth at the minimum speed needed to travel to some outer planet is slowed by the Sun’s gravity to a speed far less than the orbital speed of that outer planet. Thus, there must be some way to accelerate the spacecraft when it reaches that outer planet if it is to enter orbit about it. However, if the spacecraft is accelerated to more than the minimum required, less total propellant will be needed to enter orbit about the target planet. In addition, accelerating the spacecraft early in the flight will reduce the travel time.

Rocket engines can certainly be used to increase and decrease the speed of the spacecraft. However, rocket thrust takes propellant, propellant has mass, and even a small increment Δv (delta-v) in velocity translates to far larger requirement for propellant needed to escape Earth’s gravity well. This is because not only must the primary stage engines lift that extra propellant, they must also lift more propellant still, to lift that additional propellant. Thus the lift-off mass requirement increases exponentially with an increase in the required delta-v of the spacecraft.

Since a gravity assist maneuver can change the speed of a spacecraft without expending propellant, if and when possible, combined with aerobraking, it can save significant amounts of propellant.

As an example, the Messenger mission used gravity assist maneuvering to slow the spacecraft on its way to Mercury; however, since Mercury has almost no atmosphere, aerobraking could not be used for insertion into orbit around it.

Journeys to the nearest planets, Mars and Venus, use a Hohmann transfer orbit, an elliptical path which starts as a tangent to one planet’s orbit round the Sun and finishes as a tangent to the other. This method uses very nearly the smallest possible amount of fuel, but is very slow — it can take over a year to travel from Earth to Mars (fuzzy orbits use even less fuel, but are even slower).

Similarly it might take decades for a spaceship to travel to the outer planets (JupiterSaturnUranus, and Neptune) using a Hohmann transfer orbit, and it would still require far too much propellant, because the spacecraft would have to travel for 800 million km (500 million miles) or more against the force of the Sun’s gravity. As gravitational assist maneuvers offer the only way to gain speed without using propellant, all missions to the outer planets have used it.

The main practical limit to the use of a gravity assist maneuver is that planets and other large masses are seldom in the right places to enable a voyage to a particular destination. For example the Voyager missions which started in the late 1970s were made possible by the “Grand Tour” alignment of Jupiter, Saturn, Uranus and Neptune. A similar alignment will not occur again until the middle of the 22nd century. That is an extreme case, but even for less ambitious missions there are years when the planets are scattered in unsuitable parts of their orbits.

Another limitation is the atmosphere, if any, of the available planet. The closer the spacecraft can approach, the more boost it gets, because gravity falls off with the square of distance from a planet’s center. If a spacecraft gets too far into the atmosphere, the energy lost to drag can exceed that gained from the planet’s gravity. On the other hand, the atmosphere can be used to accomplish aerobraking. There have also been theoretical proposals to use aerodynamic lift as the spacecraft flies through the atmosphere. This maneuver, called an aerogravity assist, could bend the trajectory through a larger angle than gravity alone, and hence increase the gain in energy.

Interplanetary slingshots using the Sun itself are not possible because the Sun is at rest relative to the Solar System as a whole. However, thrusting when near the Sun has the same effect as the powered slingshot described below. This has the potential to magnify a spacecraft’s thrusting power enormously, but is limited by the spacecraft’s ability to resist the heat.

An interstellar slingshot using the Sun is conceivable, involving for example an object coming from elsewhere in our galaxy and swinging past the Sun to boost its galactic travel. The energy and angular momentum would then come from the Sun’s orbit around the Milky Way. This concept features prominently in Arthur C. Clarke‘s 1972 award-winning novel Rendezvous With Rama; his story concerns an interstellar spacecraft that uses the Sun to perform this sort of maneuver, and in the process alarms many nervous humans.

Another theoretical limit is based on general relativity. The deepest gravity wells are those found around black holes, but if a spacecraft gets close to the Schwarzschild radius of a black hole, space becomes so curved that slingshot orbits require more energy to escape than the energy that could be added by the black hole’s motion.

rotating black hole might provide additional assistance, if its spin axis is aligned the right way. General relativity predicts that a large spinning mass-produces frame-dragging—close to the object, space itself is dragged around in the direction of the spin. Any ordinary rotating object produces this effect. Although attempts to measure frame dragging about the Sun have produced no clear evidence, experiments performed by Gravity Probe B have detected frame-dragging effects caused by Earth.

General relativity predicts that a spinning black hole is surrounded by a region of space, called the ergosphere, within which standing still (with respect to the black hole’s spin) is impossible, because space itself is dragged at the speed of light in the same direction as the black hole’s spin. The Penrose process may offer a way to gain energy from the ergosphere, although it would require the spaceship to dump some “ballast” into the black hole, and the spaceship would have had to expend energy to carry the “ballast” to the black hole.

What is the Gravity Assist?

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Slingshot Manoeuvre

In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense. Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed and/or redirect its path.

cgi of slingshot gravity assist.

The “assist” is provided by the motion of the gravitating body as it pulls on the spacecraft. The technique was first proposed as a mid-course manoeuvre in 1961 by Michael Minovitch working on the three-body problem. It was used by interplanetary probes from Mariner 10 onwards, including the two Voyager probes’ notable flybys of Jupiter and Saturn.

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The Mercury Two

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Mariner and the Messenger

Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus.

Mariner 10 was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were allocated to the Voyager program and re-designated Voyager 1 and Voyager 2).

The mission objectives were to measure Mercury’s environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to obtain experience with a dual-planet gravity assist mission. Mariner 10’s science team was led by Bruce C. Murray at the Jet Propulsion Laboratory.

Mariner_10

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The Orbit of Mercury

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Mercury has the most eccentric orbit of all the planets; its eccentricity is 0.21 with its distance from the Sun ranging from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi).

Mercury’s higher velocity when it is near perihelion is clear from the greater distance it covers in each 5-day interval. 

This varying distance to the Sun, combined with a 3:2 spin–orbit resonance of the planet’s rotation around its axis, result in complex variations of the surface temperature. This resonance makes a single day on Mercury last exactly two Mercury years, or about 176 Earth days.

Mercury_Mariner10

Mercury’s orbit is inclined by 7 degrees to the plane of Earth’s orbit (the ecliptic), as shown in the diagram on the right. As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between Earth and the Sun. This occurs about every seven years on average.

Mercury’s axial tilt is almost zero, with the best measured value as low as 0.027 degrees. This is significantly smaller than that of Jupiter, which has the second smallest axial tilt of all planets at 3.1 degrees. This means that to an observer at Mercury’s poles, the center of the Sun never rises more than 2.1 arcminutes above the horizon.

At certain points on Mercury’s surface, an observer would be able to see the Sun rise about halfway, then reverse and set before rising again, all within the same Mercurian day. This is because approximately four Earth days before perihelion, Mercury’s angular orbital velocity equals its angular rotational velocity so that the Sun’s apparent motion ceases; closer to perihelion, Mercury’s angular orbital velocity then exceeds the angular rotational velocity. Thus, to a hypothetical observer on Mercury, the Sun appears to move in a retrograde direction. Four Earth days after perihelion, the Sun’s normal apparent motion resumes.

For the same reason, there are two points on Mercury’s equator, 180 degrees apart in longitude, at either of which, around perihelion in alternate Mercurian years (once a Mercurian day), the Sun passes overhead, then reverses its apparent motion and passes overhead again, then reverses a second time and passes overhead a third time, taking a total of about 16 Earth-days for this entire process. In the other alternate Mercurian years, the same thing happens at the other of these two points. The amplitude of the retrograde motion is small, so the overall effect is that, for two or three weeks, the Sun is almost stationary overhead, and is at its most brilliant because Mercury is at perihelion, its closest to the Sun. This prolonged exposure to the Sun at its brightest makes these two points the hottest places on Mercury. Conversely, there are two other points on the equator, 90 degrees of longitude apart from the first ones, where the Sun passes overhead only when the planet is at aphelion in alternate years, when the apparent motion of the Sun in Mercury’s sky is relatively rapid.

Mercury attains inferior conjunction (nearest approach to Earth) every 116 Earth days on average, but this interval can range from 105 days to 129 days due to the planet’s eccentric orbit. Mercury can come as near as 82.2 Gm to Earth, and that is slowly declining: The next approach to within 82.1 Gm is in 2679, and to within 82 Gm in 4487, but it will not be closer to Earth than 80 Gm until AD 28,622. Its period of retrograde motion as seen from Earth can vary from 8 to 15 days on either side of inferior conjunction. This large range arises from the planet’s high orbital eccentricity.

Longitude convention

The longitude convention for Mercury puts the zero of longitude at one of the two hottest points on the surface, as described above. However, when this area was first visited, by Mariner 10, this zero meridian was in darkness, so it was impossible to select a feature on the surface to define the exact position of the meridian. Therefore, a small crater further west was chosen, called Hun Kal, which provides the exact reference point for measuring longitude. The center of Hun Kal defines the 20° West meridian. A 1970 International Astronomical Union resolution suggests that longitudes be measured positively in the westerly direction on Mercury. The two hottest places on the equator are therefore at longitudes 0°W and 180°W, and the coolest points on the equator are at longitudes 90°W and 270°W. However, the MESSENGER project uses an east-positive convention.

Mercury -Graph of internal structure

For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping the same face directed towards the Sun, in the same way that the same side of the Moon always faces Earth. Radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun; the eccentricity of Mercury’s orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly still in Mercury’s sky.

The original reason astronomers thought it was synchronously locked was that, whenever Mercury was best placed for observation, it was always nearly at the same point in its 3:2 resonance, hence showing the same face. This is because, coincidentally, Mercury’s rotation period is almost exactly half of its synodic period with respect to Earth. Due to Mercury’s 3:2 spin–orbit resonance, a solar day (the length between two meridian transits of the Sun) lasts about 176 Earth days. A sidereal day (the period of rotation) lasts about 58.7 Earth days.

Simulations indicate that the orbital eccentricity of Mercury varies chaotically from nearly zero (circular) to more than 0.45 over millions of years due to perturbations from the other planets. This is thought to explain Mercury’s 3:2 spin–orbit resonance (rather than the more usual 1:1), because this state is more likely to arise during a period of high eccentricity. Numerical simulations show that a future secular orbital resonant perihelion interaction with Jupiter may cause the eccentricity of Mercury’s orbit to increase to the point where there is a 1% chance that the planet may collide with Venus within the next five billion years.

Magnetic field on Mercury

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Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field. According to measurements taken by Mariner 10, it is about 1.1% the strength of Earth’s. The magnetic-field strength at Mercury’s equator is about300 nT. Like that of Earth, Mercury’s magnetic field is dipolar. Unlike Earth, Mercury’s poles are nearly aligned with the planet’s spin axis. Measurements from both the Mariner 10 and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable.

Earth-solid-inner-core-Mercury-solid-inner-core-comparison-graph

It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth. This dynamo effect would result from the circulation of the planet’s iron-rich liquid core. Particularly strong tidal effects caused by the planet’s high orbital eccentricity would serve to keep the core in the liquid state necessary for this dynamo effect.

Mercury’s magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The planet’s magnetosphere, though small enough to fit within Earth, is strong enough to trap solar wind plasma. This contributes to the space weathering of the planet’s surface. Observations taken by the Mariner 10 spacecraft detected this low energy plasma in the magnetosphere of the planet’s nightside. Bursts of energetic particles were detected in the planet’s magnetotail, which indicates a dynamic quality to the planet’s magnetosphere.

Mercury -Graph of internal structure

During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury’s magnetic field can be extremely “leaky”. The spacecraft encountered magnetic “tornadoes” – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to 800 km wide or a third of the radius of the planet. These “tornadoes” form when magnetic fields carried by the solar wind connect to Mercury’s magnetic field. As the solar wind blows past Mercury’s field, these joined magnetic fields are carried with it and twist up into vortex-like structures. These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet’s magnetic shield through which the solar wind may enter and directly impact Mercury’s surface.

The process of linking interplanetary and planetary magnetic fields, called magnetic reconnection, is common throughout the cosmos. It occurs in Earth’s magnetic field, where it generates magnetic tornadoes as well. The MESSENGER observations show the reconnection rate is ten times higher at Mercury. Mercury’s proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER.

 

On The Surface of Mercury

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Mercury’s surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years.

 

Coley-Mercury-surface                                   Mercury_Mariner10

 

 

 

 

Last Images from The Messenger Probe 

 

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The Internal Structure of Mercury

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Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 kilometres (1,516.0 mi). Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.

Mercury consists of approximately 70% metallic and 30% silicate material. Mercury’s density is the second highest in the Solar System at 5.427 g/cm3, only slightly less than Earth’s density of 5.515 g/cm3. If the effect of gravitational compression were to be factored out, the materials of which Mercury is made would be denser, with an uncompressed density of 5.3 g/cm3 versus Earth’s 4.4 g/cm3.

Mercury -Graph of internal structure

1. Crust: 100–300 km thick
2. Mantle: 600 km thick
3. Core: 1,800 km radius

Mercury’s density can be used to infer details of its inner structure. Although Earth’s high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not as compressed. Therefore, for it to have such a high density, its core must be large and rich in iron.

Geologists estimate that Mercury’s core occupies about 42% of its volume; for Earth this proportion is 17%. Research published in 2007 suggests that Mercury has a molten core. Surrounding the core is a 500–700 km mantle consisting of silicates. Based on data from theMariner 10 mission and Earth-based observation, Mercury’s crust is believed to be 100–300 km thick. One distinctive feature of Mercury’s surface is the presence of numerous narrow ridges, extending up to several hundred kilometers in length. It is believed that these were formed as Mercury’s core and mantle cooled and contracted at a time when the crust had already solidified.

Mercury’s core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System’s rocky matter, and a mass approximately 2.25 times its current mass. Early in the Solar System’s history, Mercury may have been struck by a planetesimal of approximately 1/6 that mass and several thousand kilometers across. The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon.

Alternatively, Mercury may have formed from the solar nebula before the Sun’s energy output had stabilized. It would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000 K. Much of Mercury’s surface rock could have been vaporized at such temperatures, forming an atmosphere of “rock vapor” that could have been carried away by the solar wind.

A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material and not gathered by Mercury. Each hypothesis predicts a different surface composition, and two space missions, MESSENGER and BepiColombo, both will make observations to test them. MESSENGER has found higher-than-expected potassium and sulfur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because potassium and sulfur would have been driven off by the extreme heat of these events. The findings would seem to favor the third hypothesis; however, further analysis of the data is needed.

The Smallest Planet

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By The Sun

Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. Seen from Earth, it appears to move around its orbit in about 116 days, which is much faster than any other planet in the Solar System. It has no known natural satellites. The planet is named after the Roman deity Mercury, the messenger to the gods.

Because it has almost no atmosphere to retain heat, Mercury’s surface experiences the greatest temperature variation of the planets in the Solar System, ranging from 100 K (−173 °C; −280 °F) at night to 700 K (427 °C; 800 °F) during the day at some equatorial regions. The poles are constantly below 180 K (−93 °C; −136 °F). Mercury’s axis has the smallest tilt of any of the Solar System’s planets (about 130 of a degree), but it has the largest orbital eccentricity. At aphelion, Mercury is about 1.5 times as far from the Sun as it is at perihelion. Mercury’s surface is heavily cratered and similar in appearance to the Moon, indicating that it has been geologically inactive for billions of years.

Mercury is gravitationally locked and rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two years.

Because Mercury orbits the Sun within Earth’s orbit (as does Venus), it can appear in Earth’s sky in the morning or the evening, but not in the middle of the night. Also, like Venus and the Moon, it displays a complete range of phases as it moves around its orbit relative to Earth. Although Mercury can appear as a bright object when viewed from Earth, its proximity to the Sun makes it more difficult to see than Venus. Two spacecraft have visited Mercury: Mariner 10 flew by in the 1970s; and MESSENGER, launched in 2004, orbited Mercury over 4,000 times in four years, before exhausting its fuel and crashing into the planet’s surface on April 30, 2015.

The Hamburger Nebula

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Gomez’s Hamburger is believed to be a young star surrounded by a protoplanetary disk. It was initially identified as a planetary nebula, and its distance was estimated to be approximately 6500 light-years away from Earth. However, recent results suggest that this object is a young star surrounded by a protoplanetary disk, at a distance of about 900 light-years away.

It was discovered in 1985 on sky photographs obtained by Arturo Gomez, support technical staff at the Cerro Tololo Inter-American Observatory near Vicuña, Chile. The photos suggested that there was a dark band across the object, but its exact structure was difficult to determine because of the atmospheric turbulence that hampers all images taken from the ground. The star itself has a surface temperature of approximately 10,000 K.

The “buns” are light reflecting off dust, and the “burger” is the dark band of dust in the middle.

HST Image of the Gomez Hamburger

More information from a JPL news release in 2002

The Concept of Dwarf Planets

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Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the word asteroid for the smaller bodies and then stopped naming or classifying them as planets.

With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets, along with thousands of significantly smaller bodies (asteroids and comets). For almost 50 years Pluto was thought to be larger than Mercury, but with the discovery in 1978 of Pluto’s moon Charon, it became possible to measure Pluto’s mass accurately and to determine that it was much smaller than in initial estimates. It was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was still more than ten times as massive as the largest object in the asteroid belt, Ceres, it was one-fifth that of Earth’s Moon. Furthermore, having some unusual characteristics, such as large orbital eccentricity and a high orbital inclination, it became evident it was a completely different kind of body from any of the other planets.

In the 1990s, astronomers began to find objects in the same region of space as Pluto (now known as the Kuiper belt), and some even farther away. Many of these shared several of Pluto’s key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects, plutinos. This led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the bodies now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto (Quaoar, Sedna, and Eris) had been reported. It became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly if Pluto were to remain a planet.

Eris (then known as 2003 UB313) was discovered in January 2005, which was believed to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the issue became a matter of intense debate during the IAU General Assembly in August 2006. The IAU’s initial draft proposal included Charon, Eris, and Ceres in the list of planets. After many astronomers objected to this proposal, an alternative was drawn up by Uruguayan astronomer Julio Ángel Fernández, in which he created a median classification for objects large enough to be round but that had not cleared their orbits of planetesimals. Dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits.

The IAU’s final Resolution 5A preserved this three-category system for the celestial bodies orbiting the Sun. It reads:

The IAU … resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

(1) A planet1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,2 (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects,3 except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies.”

The Snowman on Vesta

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Craters-Snowman-Vesta

Shaped Like A Snowman

Vesta is the second-most-massive object in the asteroid belt after the dwarf planet Ceres, and it contributes an estimated 9% of the mass of the asteroid belt. The less-massive Pallas is slightly larger, making Vesta third in volume.

Vesta is the last remaining rocky protoplanet (with a differentiated interior) of the kind that formed the terrestrial planets. Numerous fragments of Vesta were ejected by collisions one and two billion years ago that left two enormous craters occupying much of Vesta’s southern hemisphere. Debris from these events has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, which have been a rich source of information about Vesta.

Vesta is the brightest asteroid visible from Earth. Its maximum distance from the Sun is slightly greater than the minimum distance of Ceres from the Sun,[* 2] though its orbit lies entirely within that of Ceres.

NASA’s Dawn spacecraft entered orbit around Vesta on 16 July 2011 for a one-year exploration and left orbit on 5 September 2012 heading for Ceres. Researchers continue to examine data collected by Dawn for additional insights into the formation and history of Vesta.

Wacky Craters

The smallest crater looks like the head of the snowman, with the two others making up the body, Holger Sierks, a member of Dawn’s framing camera team at the Max Planck Society in Germany, said in a press conference Monday…

“They’re very interesting to us because they appear to be shallow,” he added.

Dawn took the picture from a distance of about 3,200 miles (5,200 kilometers). The snowman image is one of several new and detailed photos of Vesta that are being released as the spacecraft begins taking scientific observations of the space rock.

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Moon Craters – Pascal

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Pascal is a lunar crater that lies near the northern limb of the Moon, on the western side of the pole. It is located to the north of the eroded crater Desargues, and just east of Brianchon. Pascal can be located by finding the crater Carpenter and then following the surface to the northwest towards the limb. However the visibility of this formation can be affected by libration.

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This crater has undergone a degree of impact erosion that has left its features softened and rounded. The rim can still be followed around the perimeter, but it is no longer sharp-edged and the interior terraces have been all but worn away. Several craters lie across the outer rim, including the sharp-edged Pascal F intruding into the northwest rim; a more worn Pascal A intruding into the southwest; and the small, bowl-shaped Pascal G along the southeast rim.

Within the wide inner walls is a nearly level interior floor that has been resurfaced by lava. At the midpoint is a low ridge, forming a minor central peak. There are tiny craters at the north end of the floor, and at the northeast end of the central ridge. There is also a small chain of craterlets lying across the northeast inner wall.

Just to the north of Pascal is Poncelet C, a satellite crater of the lava-flooded Poncelet to the east. The rim of this crater is bisected by several grooves in the surface, one of which crosses the southeast rim and cuts across tangentially to the north-eastern rim of Pascal.

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The Moon Craters – Mare Orientale

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Discover the Moon’s Features

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Mare Orientale (“eastern sea” in Latin) is a lunar mare. It is located on the western border of the Moon‘s nearside and is difficult to see from an Earthbound perspective. Images from spacecraft have revealed it to be one of the most striking large scale lunar features, resembling a target ring bullseye.

During the 1960s, rectified images of Mare Orientale by Gerard Kuiper at the Lunar and Planetary Laboratory gave rise to the notion of it being an impact crater. The mare is about 900 kilometres (560 mi) across and was formed by the impact of an asteroid-sized object. Compared with most other lunar basins, Mare Orientale is less flooded by mare basalts, so that a lot of the basin structure is visible. The basalt in the central portion of Mare Orientale is probably less than 1 km (0.62 mi) in thickness which is much less than mare basins on the earth-facing side of the moon.

The collision caused ripples in the lunar crust, resulting in the three concentric circular features. The innermost rings of this vast, multi-ringed crater are the inner and outer Montes Rook, and the outermost ring are the Montes Cordillera, 930 km (580 mi) in diameter. Outward from here, ejecta extend some 500 km (310 mi) from the foot of the mountains and form a rough surface with hummocks and with features radially aligned towards the center.

The Apollo program did not sample rocks from Mare Orientale so its precise age is not known. However, it is the Moon’s most recent impact basin, probably rather younger than the Imbrium Basin, which is about 3.85 billion years old. The surrounding basin material is of the Lower Imbrian epoch with the mare material being of the Upper Imbrian epoch.

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Mars and The Grand Canyon

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Valles Marineris

Valles Marineris (Latin for Mariner Valleys, named after the Mariner 9 Mars orbiter of 1971–72 which discovered it) is a system of canyons that runs along the Martian surface east of the Tharsis region. At more than 4,000 km (2,500 mi) long, 200 km (120 mi) wide and up to 7 km (23,000 ft) deep, the Valles Marineris rift system is one of the larger canyons of the Solar System, surpassed only by the rift valleys of Earth.

Valles Marineris is located along the equator of Mars, on the east side of the Tharsis Bulge, and stretches for nearly a quarter of the planet’s circumference. The Valles Marineris system starts in the west with Noctis Labyrinthus; proceeding to the east are Tithoniumand Ius chasmata, then MelasCandor and Ophir chasmata, then Coprates Chasma, then GangesCapri and Eos chasmata; finally it empties into an outflow channel region containing chaotic terrain that ends in the basin of Chryse Planitia. It has been recently suggested that Valles Marineris is a large tectonic “crack” in the Martian crust. Most researchers agree that this formed as the crust thickened in the Tharsis region to the west, and was subsequently widened by erosion. However, near the eastern flanks of the rift, there appear to be some channels that may have been formed by water or carbon dioxide.

valles-marineris-feature-on-mars

There have been many different theories about the formation of Valles Marineris that have changed over the years. Ideas in the 1970s were erosion by water or thermokarst activity, which is the melting of permafrost in glacial climes. Thermokarst activity may contribute, but erosion by water is a problematic mechanism because liquid water cannot exist in most current Martian surface conditions, which typically experience about 1% of Earth’s atmospheric pressure and a temperature range of 148 K (−125 °C; −193 °F) to 310 K (37 °C; 98 °F) kelvin. However, scientists agree that there was liquid water flowing on the Martian surface in the past. Valles Marineris may have been formed by flowing water at this time. Another hypothesis by McCauley in 1972 was that the canyons formed by withdrawal of subsurface magma. Around 1989 Tanaka and Golombek proposed a theory of formation by tensional fracturing. The most agreed upon theory today is that Valles Marineris was formed by rift faults like the East African Rift, later made bigger by erosion and collapsing of the rift walls.

Because Valles Marineris is thought to be a large rift valley, its formation is closely tied with the formation of the Tharsis Bulge. The Tharsis Bulge was formed from the Noachian to Late Hesperian period of Mars, in three stages. The first stage consisted of a combination of volcanism and isostatic uplift; soon, however, thevolcanism loaded the crust to a point at which the crust could no longer support the added weight of Tharsis, leading to widespread graben formation in the elevated regions of Tharsis. Stage two consisted of more volcanism and a loss of isostatic equilibrium; the source regions of the volcanism no longer resided underneath Tharsis, creating a very large load. Finally, the crust failed to hold up Tharsis and radial fractures, like Valles Marineris, formed. Stage three mainly consisted of more volcanism and asteroid impacts. The crust, having already reached its failure point, just stayed in place and younger volcanoes formed. Tharsis volcanism involved very low viscosity magma, forming shield volcanoes similar to those of the Hawaiian Island chain, but, because there is minor or no current active plate tectonics on Mars, the hotspot activity led to very long histories of repeated volcanic eruptions at the same spots, creating some of the largest volcanoes in the solar system, including the biggest, Olympus Mons.

Landslides have left numerous deposits on the floor of Valles Marineris and contributed to widening it. Possible triggers of landslides are quakes caused by tectonic activity or impact events. Both types of events release seismic waves that accelerate the ground at and below the surface. Mars is much less tectonically active than Earth, and Mars-quakes are unlikely to have provided seismic waves of the required magnitude. Most sizable craters on Mars date to the Late Heavy Bombardment, 4.1 to 3.8 billion years ago (the Noachian period), and are older than the landslide deposits in Valles Marineris. However, three craters (including the crater Oudemans) have been identified, on the basis of their proximity and later dates, as ones whose formation may have caused some of the landslides.

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What Is a Dwarf Planet?

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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. That is, it is in direct orbit of the Sun, and is massive enough for its shape to be in hydrostatic equilibrium under its own gravity, but has not cleared the neighborhood around its orbit.

Pluto Motion Moving Image

Pluto

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Dark Sky Nebula

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The Coalsack

The Coalsack Dark Nebula (or simply the Coalsack) is the most prominent dark nebula in the skies, easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way. It was known pre-historically in the Southern Hemisphere and was observed by Vicente Yáñez Pinzón in 1499. The Coalsack is located at a distance of approximately 600 light years away from Earth, in the constellation Crux.

ColeyArtAstro-with-coalsacknebula-in-background

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Asteroid could wipe out earth in 2880

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Or so it was thought…

NASA image of 29075 (1950da) Orbit graph

Orbit graph

It was really thought this was the time that an asteroid would hit Earth and end all life upon it.

It makes for great apocalyptic sensational head-lines like it did a few years ago – though this blogger put those head-lines into perspective! 

 

You Can Read The Official NASA Page By Clicking This Link

 

Information Background

(29075) 1950 DA is a near-Earth asteroid. Among asteroids more than 1 km in diameter, it is notable for having the highest known probability of impacting Earth. In 2002, it had the highest Palermo rating with a value of 0.17 for a possible collision in 2880. In 2013, the odds of an Earth impact in 2880 were estimated as 1 in 4,000 (0.025%) with a Palermo rating of −0.83. In 2014, the odds of an Earth impact were further reduced to only 1 in 20,000 (0.005%) with a Palermo rating of −1.81. 1950 DA is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future.

Discovery and name

1950 DA was first discovered on February 23, 1950, by Carl A. Wirtanen at Lick Observatory. It was observed for seventeen days and then lost because the short observation arc resulted in large uncertainties in Wirtanen’s orbital solution. On December 31, 2000, it was recovered as 2000 YK66 and two hours later was recognized as 1950 DA.

On March 5, 2001, 1950 DA made a close approach to Earth of 0.0520726 AU (7,789,950 km; 4,840,450 mi). It was studied by radar at the Goldstone and Arecibo observatories from March 3 to 7, 2001.

The studies showed that the asteroid has a mean diameter of 1.1–1.4 km. Optical lightcurve analysis by Lenka Sarounova and Petr Pravec shows that its rotation period is 2.1216 ± 0.0001 hours. Due to its short rotation period and high radar albedo, 1950 DA is thought to be fairly dense (more than 3 g/cm³) and likely composed of nickeliron.

Possible Earth impact

That 1950 DA has one of the best-determined asteroid orbital solutions is due to a combination of:

  • an orbit moderately inclined (12 degrees) to the ecliptic plane (reducing in-plane perturbations)
  • high-precision radar astrometry, which provides its distance and is complementary to visual-wavelength measurements of angular positions
  • a 64-yearobservation arc
  • an uncertainty region controlled byresonance

Main-belt asteroid 78 Diana (~125 km in diameter) will pass about 0.003 AU (450,000 km; 280,000 mi) from 1950 DA on August 5, 2150. At that distance and size, Diana will perturb 1950 DA enough so that the change in trajectory is notable by 2880 (730 years later). In addition, over the intervening time, 1950 DA’s rotation will cause its orbit to slightly change as a result of the Yarkovsky effect. Modeling suggests 1950 DA is a retrograde rotator. If 1950 DA continues on its present orbit, it may approach Earth on March 16, 2880. Both trajectories pass many millions of kilometers from Earth, so 1950 DA does not have a significant chance of impacting Earth. As of 19 August 2014, the probability of an impact in 2880 is 1 in 20,000 (0.005%). (A collision is likely to be ruled out as more data becomes available).

The energy released by a collision with an object the size of 1950 DA would cause major effects on the climate and biosphere, which would be devastating to human civilization. The discovery of the potential impact heightened interest in asteroid deflection strategies.

The Astronomer Cassini

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Cassini-Giovanni-portraitGiovanni Domenico Cassini (8 June 1625 – 14 September 1712) was an Italian mathematicianastronomerengineer, and astrologer. Cassini, also known as Gian Domenico Cassini, was born in Perinaldo, near Imperia, at that time in the County of Nice under the control of the Republic of Genoa. Cassini is known for his work in the fields of astronomy and engineering. Cassini most notably discovered four satellites of the planet Saturn and noted the division of the rings of Saturn (with the Cassini Division becoming named after him). Giovanni Domenico Cassini was also the first of his family to begin work on the project of creating a topographic map of France. Launched in 1997, the Cassini spaceprobe was named after him and became the fourth to visit Saturn and the first to orbit the planet.

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Comet Shoemaker–Levy 9 and Jupiter met one day

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Comet Shoemaker–Levy 9 (formally designated D/1993 F2) was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extra-terrestrial collision of Solar System objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide. The collision provided new information about Jupiter and highlighted its role in reducing space debris in the inner Solar System.

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The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy. Shoemaker–Levy 9, at the time captured by and orbiting Jupiter, was located on the night of March 24, 1993, in a photograph taken with the 40 cm (16 in) Schmidt telescope at the Palomar Observatory in California. It was the first comet observed to be orbiting a planet, and had probably been captured by the planet around 20 – 30 years earlier.

Calculations showed that its unusual fragmented form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker–Levy 9 passed within Jupiter’s Roche limit, and Jupiter’s tidal forces had acted to pull apart the comet. The comet was later observed as a series of fragments ranging up to 2 km (1.2 mi) in diameter. These fragments collided with Jupiter’s southern hemisphere between July 16 and July 22, 1994, at a speed of approximately 60 km/s (37 mi/s) or 216,000 km/h (134,000 mph). The prominent scars from the impacts were more easily visible than the Great Red Spot and persisted for many months.

Discovery

While conducting a program of observations designed to uncover near-Earth objects, the Shoemakers and Levy discovered Comet Shoemaker–Levy 9 on the night of March 24, 1993 in a photograph taken with the 0.4 m (1.3 ft) Schmidt telescope at the Palomar Observatory in California. The comet was thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program.

Comet Shoemaker–Levy 9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, hence its name. It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature. The discovery was announced in IAU Circular 5725 on March 27, 1993.

The discovery image gave the first hint that comet Shoemaker–Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region about 50 arcseconds long and 10 arcseconds wide. Brian G. Marsden of the Central Bureau for Astronomical Telegrams noted that the comet lay only about 4 degrees from Jupiter as seen from Earth, and that while this could of course be a line of sight effect, its apparent motion in the sky suggested that it was physically close to the giant planet. Because of this, he suggested that the Shoemakers and David Levy had discovered the fragments of a comet that had been disrupted by Jupiter‘s gravity.

Jupiter-orbiting comet

Orbital studies of the new comet soon revealed that it was orbiting Jupiter rather than the Sun, unlike all other comets known at the time. Its orbit around Jupiter was very loosely bound, with a period of about 2 years and an apojove (the point in the orbit farthest from the planet) of 0.33 astronomical units (49,000,000 km). Its orbit around the planet was highly eccentric (e = 0.9986).

Tracing back the comet’s orbital motion revealed that it had been orbiting Jupiter for some time. It seems most likely that it was captured from a solar orbit in the early 1970s, although the capture may have occurred as early as the mid-1960s.[7] Several other observers found images of the comet in precovery images obtained before March 24, including Kin Endate from a photograph exposed on March 15, S. Otomo on March 17, and a team led by Eleanor Helin from images on March 19. No precovery images dating back to earlier than March 1993 have been found. Before the comet was captured by Jupiter, it was probably a short-period comet with an aphelion just inside Jupiter’s orbit, and a perihelion interior to the asteroid belt.

The volume of space within which an object can be said to orbit Jupiter is defined by Jupiter’s Hill sphere (also called the Roche sphere). When the comet passed Jupiter in the late 1960s or early 1970s, it happened to be near its aphelion, and found itself slightly within Jupiter’s Hill sphere. Jupiter’s gravity nudged the comet towards it. Because the comet’s motion with respect to Jupiter was very small, it fell almost straight toward Jupiter, which is why it ended up on a Jupiter-centric orbit of very high eccentricity – that is to say, the ellipse was nearly flattened out.

The comet had apparently passed extremely close to Jupiter on July 7, 1992, just over 40,000 km (25,000 mi) above the planet’s cloud tops – a smaller distance than Jupiter’s radius of 70,000 km (43,000 mi), and well within the orbit of Jupiter’s innermost moon Metis and the planet’s Roche limit, inside which tidal forces are strong enough to disrupt a body held together only by gravity. Although the comet had approached Jupiter closely before, the July 7 encounter seemed to be by far the closest, and the fragmentation of the comet is thought to have occurred at this time. Each fragment of the comet was denoted by a letter of the alphabet, from “fragment A” through to “fragment W”, a practice already established from previously observed broken-up comets.

More exciting for planetary astronomers was that the best orbital calculations suggested Coleyartastro-Coleyartfiasco-Foreground-Portrait-TNthat the comet would pass within 45,000 km (28,000 mi) of the center of Jupiter, a distance smaller than the planet’s radius, meaning that there was an extremely high probability that SL9 would collide with Jupiter in July 1994. Studies suggested that the train of nuclei would plow into Jupiter’s atmosphere over a period of about five days.

 

 

 

Our Sun’s Closest Neighbour

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Proxima Centauri (Latin proxima, meaning “next to” or “nearest to”) is a red dwarf about 4.24 light-years from the Sun, inside the G-cloud, in the constellation of Centaurus. It was discovered in 1915 by Scottish astronomer Robert Innes, the Director of the Union Observatory in South Africa, and is the nearest known star to the Sun, although it is too faint to be seen with the naked eye, with an apparent magnitude of 11.05. Its distance to the second- and third-nearest stars, which form the bright binary Alpha Centauri, is 0.237 ± 0.011 ly (15,000 ± 700 AU). Proxima Centauri is very likely part of a triple star system with Alpha Centauri A and B, but its orbital period may be greater than 500,000 years.

Because of the proximity of this star, its distance from the Earth and angular diameter can be measured directly, from which it can be determined that its diameter is about one-seventh of that of the Sun. Proxima Centauri’s mass is about an eighth of the Sun’s (M), and its average density is about 40 times that of the Sun. Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star’s magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The mixing of the fuel at Proxima Centauri’s core through convection and the star’s relatively low energy-production rate suggest that it will be a main-sequence star for another four trillion years, or nearly 300 times the current age of the universe.

Searches for companions orbiting Proxima Centauri have been unsuccessful, ruling out the presence of brown dwarfs and supermassive planets. Precision radial velocity surveys have also ruled out the presence of super-Earths within the star’s habitable zone. The detection of smaller objects will require the use of new instruments, such as the James Webb Space Telescope, which is scheduled for deployment in 2018. Because Proxima Centauri is a red dwarf and a flare star, whether a planet orbiting it could support life is disputed. Nevertheless, because of the star’s proximity to Earth, it has been proposed as a destination for interstellar travel.

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The Teapot In The Night Sky

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It’s Found in Sagittarius

teapot in Sagittarius constellation

“Teapot”

As seen from the northern hemisphere, the constellation’s brighter stars form an easily recognizable asterism known as ‘the Teapot‘. The stars δ Sgr (Kaus Media), ε Sgr (Kaus Australis), ζ Sgr (Ascella), and φ Sgr (Nanto) form the body of the pot; λ Sgr (Kaus Borealis) is the point of the lid; γ2 Sgr (Alnasl) is the tip of the spout; and σ Sgr (Nunki) and τ Sgr (the closest bright star to the possible origin of the Wow! signal) the handle.

Marking the bottom of the teapot’s “handle” (or the shoulder area of the archer, are the bright star (2.59 magnitude) Zeta Sagittarii (ζ Sgr), named Ascella, and the fainter Tau Sagittarii (τ Sgr).

To complete the teapot metaphor, under good conditions, a particularly dense area of the Milky Way can be seen rising in a north-westerly arc above the spout, like a puff of steam rising from a boiling kettle.

The constellation as a whole is often depicted as having the rough appearance of a stick-figure archer drawing its bow, with the fainter stars providing the outline of the horse’s body. Sagittarius famously points its arrow at the heart of Scorpius, represented by the reddish star Antares, as the two constellations race around the sky. Following the direct line formed by Delta Sagittarii (δ Sgr) and Gamma Sagittarii (γ Sgr) leads nearly directly to Antares. , Fittingly, Gamma Sagittarii is named Alnasl, the Arabic word for “arrowhead”, and Delta Sagittarii is called Kaus Media, the “center of the bow,” from which the arrow protrudes. Kaus Media bisects Lambda Sagittarii (λ Sgr) andEpsilon Sagittarii (ε Sgr), whose names Kaus Borealis and Kaus Australis refer to the northern and southern portions of the bow, respectively.

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Mass of The Sun

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Massive Star – The Main Important One for us anyway!

 

The Sun does not have enough mass to explode as a supernova. Instead it will exit the main sequence in approximately 5.4 billion years and start to turn into a red giant. It is
calculated that the Sun will become sufficiently large to engulf the current orbits of the solar system‘s inner planets, possibly including Earth.

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Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled, and the Earth will be hotter than Venus is today. Once the core hydrogen is exhausted in 5.4 billion years, the Sun will expand into a subgiant phase and slowly double in size over about half a billion years.

It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous. This then starts the red giant branch (RGB) phase where the Sun will spend around a billion years and lose around a third of its mass.

Large Image Of The Sun - Our Star

The Sun – Our Star

 

 

After RGB the Sun now has only about 120 million years of active life left, but they are highly eventful. First the core ignites violently in the helium flash, and the Sun shrinks back to around 10 times its current size with 50 times the luminosity, with a temperature a little lower than today.

sun-coleynotesheader

It has now reached the red clump or horizontal branch (HB), but a star of the Sun’s mass does not evolve blueward along the HB. Instead it just becomes mildly larger and more luminous over about 100 million years as it continues to burn helium in the core.

The SUN CME image

 

Our Star Is Massive

 

 

 

 

the Great Virgo Cluster

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Explore for Galaxies Galore

the cluster spot where Virgo is found.

Cluster Region

 

The Virgo Cluster (VC) is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo. Comprising approximately 1300 (and possibly up to 2000) member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group (LG) is an outlying member. However, the LG experiences the mass of the VC as the Virgocentric flow. It is estimated that the VC’s mass is 1.2×1015 M out to 8 degrees of the cluster’s center or a radius of about 2.2 Mpc.

Many of the brighter galaxies in this cluster, including the giant elliptical galaxy Messier 87, were discovered in the late 1770s and early 1780s and subsequently included in Charles Messier‘s catalogue of non-cometary fuzzy objects. Described by Messier as nebulae without stars, their true nature was not recognized until the 1920s.

The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Many of the member galaxies of the cluster are visible with a small telescope. Its brightest member is the elliptical galaxy Messier 49; however its most famous member is the also elliptical galaxy Messier 87, that unlike the former is located in the center of the cluster.

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See the virgo cluster in 3D…

 

Fraunhofer Sun Lines

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In physics and optics, the Fraunhofer lines are a set of spectral lines named after the German physicist Joseph von Fraunhofer (1787–1826) . The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun.

A Fraunhofer Portrait

Fraunhofer portrait

The Fraunhofer lines are typical spectral absorption lines. These dark lines are produced whenever a cold gas is between a broad spectrum photon source and the detector. In this case, a decrease in the intensity of light in the frequency of the incident photon is seen as the photons are absorbed, then re-emitted in random directions, which are mostly in directions different from the original one.

This results in an absorption line, since the narrow frequency band of light initially traveling toward the detector, has been turned into heat or re-emitted in other directions.

By contrast, if the detector sees photons emitted directly from a glowing gas, then the detector often sees photons emitted in a narrow frequency range by quantum emission processes in atoms in the hot gas, resulting in an emission line. In the Sun, Fraunhofer lines are seen from gas in the outer regions of the Sun, which are too cold to directly produce emission lines of the elements they represent.

The More Rhodopsin The Better

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Naked Eye Sky Viewing

The chemical in the eye needed is called rhodopsin..

Rhodopsin, also known as visual purple, due to its pinkish color, and ὄψις (ópsis, “sight”), is a light-sensitive receptor protein. It is a biological pigment in photoreceptor cells of the retina. Rhodopsin is the primary pigment found in rod photoreceptors. Rhodopsins belong to the G-protein-coupled receptor(GPCR) family. They are extremely sensitive to light, enabling vision in low-light conditions. Exposed to light, the pigment immediately photobleaches, and it takes about 45 minutes to regenerate fully in humans.

Visual diagram highlighting rhdopsin chemical.

Rhodopsin diagram.

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Celestial Sphere

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In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radiusconcentric with a particular celestial body. All objects in the observer’s sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.

tn-4earth-coleyatastro

Love Earth

Introduction

Because astronomical objects are at such remote distances, casual observation of the sky offers no information on the actual distances. All objects seem equally far away, as if fixed to the inside of a sphere of large but unknown radius, which rotates from east to west overhead while underfoot, the celestial body seems to stand still. For purposes of spherical astronomy, which is concerned only with the directions to objects, it makes no difference whether this is actually the case, or if it is the celestial body which rotates while the celestial sphere stands still.

The celestial sphere can be considered to be infinite in radius. This means any point within it, including that occupied by the observer, can be considered the center. It also means that all parallel lines, be they millimetres apart or across the Solar System from each other, will seem to intersect the sphere at a single point, analogous to the vanishing point of graphical perspective. All parallel planes will seem to intersect the sphere in a coincident great circle (a “vanishing circle”). Conversely, observers looking toward the same point on an infinite-radius celestial sphere will be looking along parallel lines, and observers looking toward the same great circle, along parallel planes. On an infinite-radius celestial sphere, all observers see the same things in the same direction.

Image of Earth Within The Celestial Sphere

Within The Celestial Sphere

For some objects, this is over-simplified. Objects which are relatively near to the observer (for instance, the Moon) will seem to change position against the distant celestial sphere if the observer moves far enough, say, from one side of the celestial body to the other. This effect, known as parallax, can be represented as a small offset from a mean position. The celestial sphere can be considered to be centered at the celestial body’s center, A star’s center, or any other convenient location, and offsets from positions referred to these centers can be calculated. In this way, astronomers can predict geocentric or heliocentric positions of objects on the celestial sphere, without the need to calculate the individual geometry of any particular observer, and the utility of the celestial sphere is maintained. Individual observers can work out their own small offsets from the mean positions, if necessary. In many cases in astronomy, the offsets are insignificant.

The celestial sphere can be thus be thought of as a kind of astronomical shorthand, and is applied very frequently by astronomers. For instance, the Astronomical Almanac for 2010 lists the apparent geocentric position of Earth’s Moon, 1 Jan 2010 at 0h Terrestrial Time, in equatorial coordinates, as right ascension 6h 57m 48s.86, declination +23° 30′ 05″.5. Implied in this position is that it is as projected onto the celestial sphere; any observer at any location looking in that direction would see the “geocentric Moon” in the same place against the stars. For many rough uses (for instance, calculating an approximate phase of the Moon), this position, as seen from the Earth’s center, is adequate. For applications requiring precision (for instance, calculating the shadow path of an eclipse), the Almanac gives formulae and methods for calculating the topocentric coordinates, that is, as seen from a particular place on the Earth’s surface, based on the geocentric position. This greatly abbreviates the amount of detail necessary in such almanacs, as each observer can handle their own specific circumstances.

Celestial coordinate systems

These concepts are important for understanding celestial reference systems, the methods in which the positions of objects in the sky are measured. Certain reference lines and planes on the celestial body, when projected onto the celestial sphere, form the bases of the reference systems. These include the celestial equator, axis, and the orbit. At their intersections with the celestial sphere, these form the celestial equator, the north and south celestial poles and the ecliptic, respectively. As the celestial sphere is considered infinite in radius, all observers see the celestial equator, celestial poles and ecliptic at the same place against the background stars.

Directions toward objects in the sky can be quantified by constructing, from these bases, celestial coordinate systems. Similar to the terrestrial longitude and latitude, the equatorial system of right ascension and declination specifies positions relative to the celestial equator and celestial poles. The ecliptic system of celestial longitude and celestial latitude specifies positions relative to the celestial body’s orbit. There are more coordinate systems besides the equatorial right ascension/declination system and the ecliptic system.

History

The ancients assumed the literal truth of stars attached to the celestial sphere of Earth, revolving about the Earth in one day, and a fixed Earth. The Eudoxan planetary model, on which the Aristotelian and Ptolemaic models were based, was the first geometric explanation for the “wandering” of the classical planets. The outer most of these “crystal spheres” was thought to carry the fixed stars. Eudoxus used 27 concentric spherical solids to answer Plato’s challenge: “By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?”

 

Seyfert Galaxy

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First Discovered/ Detected in 1908

Seyfert galaxies were first detected in 1908 by Edward A. Fath and Vesto Slipher, who were using the Lick Observatory to look at the spectra of astronomical objects that were thought to be “spiral nebulae“. They noticed that NGC 1068 showed six bright emission lines, which was considered unusual as most objects observed showed an absorption spectrum corresponding to stars.

 

In 1926, Edwin Hubble looked at the emission lines of NGC 1068 and two other such “nebulae” and classified them as extragalactic objects. In 1943, Carl Keenan Seyfert discovered more galaxies similar to NGC 1068 and reported that these galaxies have very bright stellar-like nuclei that produce broad emission lines. In 1944 Cygnus A was detected at 160 MHz, and detection was confirmed in 1948 when it was established that it was a discrete source.

Its double radio structure became apparent with the use of interferometry. In the next few years, other radio sources such as supernova remnants were discovered. By the end of the 1950s, more important characteristics of Seyfert galaxies were discovered, including the fact that their nuclei are extremely compact (< 100 pc, i.e. “unresolved”), have high mass (≈109±1 solar masses), and the duration of peak nuclear emissions is relatively short (>108 years).

Source

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisationemission lines, but unlike quasars, their host galaxies are clearly detectable.

Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material.

Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.

Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.

Henry Draper

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THE FIRST TO PHOTOGRAPH NEBULA

HIS Life and work

Henry Draper (March 7, 1837 – November 20, 1882) was an American doctor and amateur astronomer. He is best known today as a pioneer of astrophotography.

Image of Henry Draper with Telescope

Henry Draper

Henry Draper’s father, John William Draper, was an accomplished doctor, chemist, botanist, and professor at New York University; he was also the first to photograph the moon through a telescope in the winter of 1839–1840. Draper’s mother was Antonia Coetana de Paiva Pereira Gardner, daughter of the personal physician to the Emperor of Brazil. His niece, Antonia Maury was also an astronomer.

He graduated from New York University School of Medicine, at the age of 20, in 1857. He worked first as a physician at Bellevue Hospital, and later as both a professor and dean of medicine at New York University (NYU). In 1867 he married Mary Anna Palmer, a wealthy socialite.

Draper was one of the pioneers of the use of astrophotography. In 1872, he took a stellar spectrum that showed absorption lines, others, such as Joseph FraunhoferLewis Morris Rutherfurd and Angelo Secchi, preceded him in that ambition.

He resigned his chair in the medical department in 1873, to allow for more time for original research.

He directed an expedition to photograph the 1874 transit of Venus, and was the first to photograph the Orion Nebula, on September 30, 1880. Using his 11 inch Clark Brothers photographic refractor he took a 50 minute exposure. He photographed the spectrum of Jupiter in 1880.

Draper’s observatory, where he took his much-admired photographs of the moon, was located in Hastings-on-HudsonNew York, and today the building functions as the Hastings-on-Hudson Historical Society.

Draper received numerous awards, including honorary LL.D. law degrees from NYU and the University of Wisconsin–Madison in 1882, a Congressional medal for directing the U.S. expedition to photograph the 1874 transit of Venus, and election to both the National Academy of Sciences and the Astronomische Gesellschaft.

In addition, he held memberships in the American Photographic Society, the American Philosophical Society, the American Academy of Arts and Sciences, and the American Association for the Advancement of Science.

After his untimely early death from double pleurisy, his widow funded the Henry Draper Medal for outstanding contributions to astrophysics and a telescope, which was used to prepare the Henry Draper Catalog of stellar spectra.

This historical Henry Draper’s telescope is now in at the Toruń Centre for Astronomy (Nicolaus Copernicus University) at Piwnice in Poland. The small crater Draper on the Moon is named in his honor.

Full biography

Henry Draper Portrait

Henry Draper Portrait