charles@utastro.UUCP (Charles Sandel) (08/20/84)
The planet Jupiter isn't a star
because it doesn't shine the way stars do.
More about it -- right after this.
August 19: What Makes Jupiter a Planet
Jupiter is more than just a large planet -- it's a giant.
In theory, you could fit all the other known planets inside Jupiter, and
still have room left over.
If this king of planets had been somewhat more massive, Earth would
bask in the light of two suns.
In other words, Jupiter approaches the lower limit in mass for stars.
Stars must contain a certain amount of mass -- to create internal pressure
great enough and internal temperatures high enough to spark thermonuclear
reactions.
These fusion reactions power the stars.
They produce the energy that we see as starlight.
Jupiter isn't a star.
It doesn't shine due to thermonuclear reactions taking place deep in its
interior.
But the interior of Jupiter is very hot,
and the planet emits nearly twice as much heat as it receives from the sun.
It's possible to explain the excess heat
from Jupiter by saying that this giant planet is still cooling
off from the process that formed it -- and the sun and the other
planets -- four-and-a-half billion years ago.
You can easily see Jupiter in the evening sky.
It's now the brightest thing up in the evening --
a bold pinpoint that arcs across the southern sky each evening.
If you've got binoculars, turn them on Jupiter --
and you might glimpse one of two of the planets largest moons!
A telescope gives an even better look --
then you can see brightly colored horizontal clouds bands
on the disk of giant Jupiter.
Script by Deborah Byrd.
(c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin
--
*>> Charles Sandel <<*
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