What is a good definition of the sun?

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Dear Tom,

What is a good definition of the sun? How did it originate and how was it formed? Why doesn’t it ever burn out?

R. W. Newren,

Dear R. W.,
Much information exists on our sun, and an excellent place to start is Wikipedia. The sun is the heavenly body that is the center of attraction and the primary source of heat and light in the Solar System. It’s mean distance from the Earth is 93 million miles, with a diameter of 864 thousand miles.

The sun formed 4.6 billion years ago when a portion of a molecular cloud that consisted primarily of hydrogen and helium collapsed, giving birth to many stars in addition to our sun. Now at 4.6 billion years of age, the sun in a middle-aged star and should last in its present state another five billion years. After consuming its hydrogen and helium, the sun will undergo about two billion years of expansions and contractions, eventually becoming a white dwarf.

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