The Sun is a normal star orbiting in an approximately circular orbit around our galaxy, the Milky Way, taking about 220 million years to complete one orbit. It is one of about 200 billion stars in the Milky Way, and like most stars, generates its energy by the thermonuclear fusion of hydrogen into helium in its interior. Such stars are called main sequence stars, because a plot of the luminosity against temperature follows a well defined curve. The Sun is so large that it can contain about a million earths, and is about 300,000 more massive than the earth. Life on the Earth, or at least life as we know it, would be impossible without the heat and light from the Sun.
The Sun has been converting hydrogen to helium for about 4.5 billion years, which is also the age of the Solar System, and will continue to do so for more than an additional 5 billion years. It will eventually die, but not before passing through what is called the red giant phase, when for a relatively brief period of time, astronomically speaking, it will swell up into a much larger, cooler and more luminous star. During that period any life on the Earth will be incinerated, if indeed the Earth survives at all.
Because the Sun is far closer than all other stars, it can be studied with a great deal of detail, and much of what we have learned about the Sun improves our understanding of other stars.
More information on the Sun can be found on the Nine Planets website.
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