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.
Even before it…
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.
Even before it…
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.
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.
Fraunhofer portrait
The Fraunhofer linesare typical spectral absorption lines. These dark lines are produced whenever a cold gas is between a broad…
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.
Fraunhofer portrait
The Fraunhofer linesare typical spectral absorption lines. These dark lines are produced whenever a cold gas is between a broad…
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.
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.
Tromsø city is the ninth largest urban area in Norway by population, and the seventh largest city in Norway by population. It is the largest city and the largest urban area in Northern Norway, and the second largest city and urban area north of the Arctic Circle in Sápmi (following Murmansk). Most of Tromsø, including the city centre, is located on the small island of Tromsøya in the county of Troms, 350 kilometres (217 mi) north of the Arctic Circle. Substantial parts of the urban area are also situated on the mainland to the east, and on parts of Kvaløya – a large island to the west. Tromsøya is connected to the mainland by the Tromsø Bridge and the Tromsøysund Tunnel, and to the island ofKvaløya by the Sandnessund Bridge. The city is warmer than most other places located on the same latitude, due to the warming effect of the Gulf Stream.
The city centre of Tromsø contains the highest number of old wooden houses in Northern Norway, the oldest house dating from 1789. The Arctic Cathedral, a modern church from 1965, is probably the most famous landmark in Tromsø. The city is a cultural centre for its region, several festivals taking place in the summer. Some of Norway’s most known musicians, Torbjørn Brundtland and Svein Berge of the electronica duo Röyksopp, both grew up and started their careers in Tromsø.
The Midnight Sun occurs from about 18 May to 26 July, although the mountains in the north block the view of the midnight sun for a few days, meaning that one can see the sun from about 21 May to 21 July. Owing to Tromsø’s high latitude, twilight is long, meaning there is no real darkness between late April and mid-August.
The sun remains below the horizon during the Polar Night from about 26 November to 15 January, but owing to the mountains the sun is not visible from 21 November to 21 January. The return of the sun is an occasion for celebration. However, because of the twilight, there is some daylight for a couple of hours even around midwinter, often with beautiful bluish light. The nights shorten quickly, and by 21 February the sun is above the horizon from 7:45 am to 4:10 pm, and 1 April from 5:50 am to 7:50 pm (daylight saving time).
The combination of snow cover and sunshine often creates intense light conditions from late February until the snow melts in the lowland (usually late April), and sunglasses are essential when skiing. Because of these diametrically different light conditions in winter, Norwegians often divide it into two seasons: Mørketid (Polar Night) and Seinvinter (late winter).
Tromsø is in the middle of the Aurora Borealis (Northern Lights) zone, and is in fact one of the best places in the world to observe this phenomenon. Because of the planet’s rotation, Tromsø moves into the aurora zone around 6 pm, and moves out again around midnight. As it is light round the clock in the summer, no aurora is visible between, late April and mid-August.
Auroras result from emissions of photons in the Earth’s upper atmosphere, above 80 km (50 mi), from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atoms returning from an excited state to ground state. They are ionized or excited by the collision of solar wind and magnetospheric particles being funneled down and accelerated along the Earth’s magnetic field lines; excitation energy is lost by the emission of a photon, or by collision with another atom or molecule:
Oxygen emissions: green or brownish-red, depending on the amount of energy absorbed.
Nitrogen emissions: blue or red; blue if the atom regains an electron after it has been ionized, red if returning to ground state from an excited state.
Oxygen is unusual in terms of its return to ground state: it can take three quarters of a second to emit green light and up to two minutes to emit red. Collisions with other atoms or molecules will absorb the excitation energy and prevent emission. Because the very top of the atmosphere has a higher percentage of oxygen and is sparsely distributed such collisions are rare enough to allow time for oxygen to emit red. Collisions become more frequent progressing down into the atmosphere, so that red emissions do not have time to happen, and eventually even green light emissions are prevented.
This is why there is a color differential with altitude; at high altitude oxygen red dominates, then oxygen green and nitrogen blue/red, then finally nitrogen blue/red when collisions prevent oxygen from emitting anything. Green is the most common of all auroras. Behind it is pink, a mixture of light green and red, followed by pure red, yellow (a mixture of red and green), and lastly, pure blue.
Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the Sun. The Earth’s magnetic field traps these particles, many of which travel toward the poles where they are accelerated toward Earth. Collisions between these ions and atmospheric atoms and molecules cause energy releases in the form of auroras appearing in large circles around the poles. Auroras are more frequent and brighter during the intense phase of the solar cycle when coronal mass ejections increase the intensity of the solar wind.
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