The Sun

People are fascinated by the stars and the distances to them. Because of these vast distances, it is very difficult to study and learn more about stars. We do however have a star closeby that can be studied without having to travel the vast distances.

Our Sun is a typical star. It provides all the life-sustaining energy for our planet and is at the centre of our Solar System.

The Sun is a hot, huge ball of gas with fierce nuclear reactions firing at its core. Light from the Sun takes 8.3 minutes to reach the Earth. The distance between the Sun and the Earth is 1 AU (Atronomical Unit). 1 AU is equal to 149 597 870 Km.

The diameter of the sun is roughly 1.4 million km. For comparison we can say that if the earth is 2cm in diameter, the sun's diameter would be 2m and it's distance would be 200m from the 2cm sized earth.

The mass of the sun is 2 x 10³º kg. That is 333000 times the mass of the earth. The density of the sun is 1400 kg/m³. Water has a density of 1000 kg/m³ and rocks of about 3000 kg/m³. This low average density with the high temperature, implies that the sun is gas.

The sun is as far as we are concerned, a very constant source of energy (heat) and light. Geological evedence on the earth indicates that the luminosity of the sun has not varied more than a few tens of a percent over the past 3.5 billion years.

What we can see of the sun directly consists of the outer layers known as the atmosphere. It does however have three substantially different zones : the photosphere, chromosphere and corona

The Photosphere has a granular structure. Each one of the granules has a lifetime of about 8 to 10 minutes. The photosphere also pulsates in waves with a period of about 5 minutes. In this time the gases in the photosphere rises and falls for hundreds of kilometers over areas of 2000 to 3000 km in diameter. The temperature in the photosphere ranges from 2781 degrees celcius to 7936 degrees celcius.

The Chromosphere begins just above the photosphere and extends about 2500 km higher where it merges into the corona. It is a 1000 times less dense than the photosphere but gets much hotter. The temperature here ranges from 4027 degrees celcius to 999727 degrees celcius. Large spears of gas, called spicules, constantly pierce the chromosphere. They spurt up to heights of 10 000 km and fade away in several minutes. They have diameters of a 1000 km and temperatures of about 7727 degrees celcius.

The Corona of the sun can be seen directly during a total solar eclipse. The temperature jumps sharply, roughly 499 727 degrees celcius in just 300 km, in the region between the chromosphere and the corona. The temperature of the corona itself is greater than 1 999 727 degrees celcius.

The corona does not end suddenly but extends into space to distances greater than indicated by its visual appearanc. Because of the high temperatures in the corona, gas streams away from the sun. Close to the sun, the speed of the gas is slow, but it increases as the distance from the sun increases. This gas stream becomes the Solar Wind. At the earth's orbit, the solar wind blows by at 450 km/sec.

Sunspots are dark blotches on the survice. They only appear darker because they are cooler than the surrounding area. Sunspots are not permanent and constantly appears and dissappears. Sunspot are born in the active region of the sun where photospheric granules separate. A tiny spot between them appears as a dark pore. Usualy more of them soon becomes visible, and after several hours, a sunspot is formed .The formation of sunspots seems to go throught a cycle. It reaches a maximum every 11 years. The next sunspot maximum will be in 2002.

Prominences are huge red clouds of hydrogen gas above the photosphere. When viewed along the sun's edge, prominences often loop and surge up into the corona. They are almost always found near a sunspot group in the active region. Prominences are also a short-lived phenomena, but may persist for weeks.

Solar Flares are short-lived violent discharges of energy. They are generated by the sunspots. About a 100 flares occur near large sunspots each day. A large flare releases the same amount of energy as a 2 billion megaton bomb. The temperature of a typical flare is 19 999 927 degrees celcius.

The sun rotates around it's own axis every 25.38 days.

Special equipment is required to view the sun. The sun and sunspots can be viewed by projecting the image of the sun through binoculars on a piece of white paper. Never look directly, with or without optical equipment, at the sun since it can cause blindness. Should you own a telescope with a sun filter, observation time must still be limited.

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