 The universe is believed to have
originated about 15 billion years ago as a dense, hot globule
of gas expanding rapidly outward. At that time, the universe
contained nothing but hydrogen and a small amount of helium.
There were no stars and no planets. The first stars probably
began to form out of hydrogen when the universe was about 100
million years old. This is how our Sun originated about 4.49
billion years ago.
Many stars came into being before the Sun was formed; many
others formed after the Sun appeared. This process continues,
and through telescopes we can now see stars forming out of
compressed pockets of hydrogen in outer space.
 In 1992, instruments aboard the Cosmic
Background Explorer (COBE) satellite showed that 99.97 percent
of the energy of the universe was released within the first
year of its origin. This evidence seems to confirm the Big
Bang theory, which holds that the universe originated from a
single violent explosion (a big bang) of a very small amount
of matter of extremely high density and temperature.
 As tronomers also theorize that 99% of
the matter in the universe is invisible, or dark matter,
composed of some kind of matter that they cannot yet
detect.
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