What is the difference between stars and planets?

On Wed, 26 Jan 2000 you wrote:

> What is the difference between stars and planets?

Astronomers quibble over the exact definition of stars and planets, but
the arguments mainly concern objects that are near the border between a
star and a planet. A good, working definition of a star is "an gaseous
object that produces light via nuclear reactions in its core, or produced
light in such a way in the past", while a planet is "an object that does
not produce its own light via nuclear reactions, and never did."

As I mentioned, there are many arguments over the exact definitions. Brown
dwarfs are often called "failed stars", because they are too small to keep
nuclear reactions going. But there is uncertainty as to the difference
between a small brown dwarf and a large planet. Likewise, using the above
definitions, a black hole could be called a star, but no astronomer would
call it one (although black holes used to be stars.)

So, in short, the above definitions are a good start, but the exact
definitions have yet to be determined!

Thanks for writing!

Sincerely,
Kurtis Williams

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