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Windows to the Universe

(29-September-2003, sirius)

Stars in the Universe
The Sun is a star.
	Here is a closer look at the Sun. A star is a ball of fire travelling through space.
The stars we see in the night sky are balls of fire travelling through space just like our sun.
	Stars group together and form galaxies. The Sun and the stars we see in the night sky form our home galaxy, called the Milky Way. It contains about 200 billion stars.
Our universe contains about 100 billion galaxies and it is about 13 million years old. The universe is vast but not infinite and thus it has boundaries.
Planets around Stars
Planets are large spheres of cool matter orbiting stars. Here is our home planet Earth.
	The Earth is one of nine planets that orbit our Sun. A solar systtem consists of a central star and planets orbiting around it.
When a star is born planets are also formed from outer orbiting material that cools. Our solar system was created about 4.6 million years ago.
	Although planets around stars are common our technology and observing techniques only recently allowed us to detect some of the larger planets orbiting nearby stars. This Hubble Space Telescope photo shows an extrasolar planet (bottom left) orbiting a nearby star.
Where there is water there is life. The modern Homo Sapiens appeared on Earth 100,000 years ago. About 6,500 years ago the Sumerians formed the first civilization recorded in modern history.
	Planets have satellites orbiting around them. The Moon is Earth's only satellite.