One of the most important features of every day life is the sun. It rises and sets, and we use it to fix our daily routine. Without it we would not receive the light and heat that provides us with energy. This star, our sun, is very unique. Most stars are visible only at night, but our sun is visible at daytime. It is the closest star to earth. Since the star is so close to us, we are able to know much about its surface.
Similar to all stars, the sun is a ball of hot gas. It has an interior as well as an atmosphere. The sun's surface is known as the photosphere. It's surface is largely uniform in brightness and becomes slightly darker on its edges. The sun has a few dark regions, called sunspots. These spots are cooler regions on its surface. Nuclear fusion is the process by which energy in the sun is formed. Groups of four hydrogen atoms are changed in to single helium atoms. Each sunspot also has a dark center, called the umbra and a less dark region, called the penumbra. These spots usually form in groups and can last for weeks. The sun rotates every 25 days, which allows us to watch the sunspots form and rotate across the surface. Sunspots are regions where the magnetic field is very strong, about 3000 times stronger than the average field of the sun or the earth. The sun is mainly composed of hydrogen and helium.
Its mean distance from the earth is one astronomical unit. It is 865,400 miles (1,392,000 km) in diameter with a volume that is about 1,300,000 times that of the earth. The sun has a temperature of about 15,000,000 degrees Kelvin. This high temperature helps with the nuclear reactions mentioned above. During a solar eclipse the chromosphere, a layer of gases above the photosphere, and the corona, an envelope of particles outside the chromosphere, can be observed.
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