Distances in the universe are
vast beyond our ability to even imagine. Astronomers have created
a measurement system which makes it possible to think about,
and compare, these huge distances. The unit that they use is
called a Light Year. A light year is equal to how far light can
travel in a year -- about 6,000,000,000,000 miles.
Nothing in the universe travels
faster than light. Light travels about 186,000 miles a second.
It travels between the earth and the moon in a little over a
second, and takes eight and a half minutes to get from the sun
to us. When light leaves the sun it takes 5 hours and 40 minutes
to get to Pluto, the outermost of our planets.
In a year, light travels 6,000,000,000,000
miles. That is a huge number! But out in space it is not much.
The star that is closest to us, Proxima Centauri, is 4.3 light
years away. Other stars spread out farther and farther from earth.
Some stars are single, like our sun, and some are double, where
two stars rotate around a common center of mass. Triple, quadruple,
and even quintuple star groups have been observed, but the gravitational
forces around them often make planetary systems unstable.
diagram of a binary system that might have planets. Look
at this site if you want to work with a multiple star system.
Stars in space are grouped in
huge systems called galaxies. Our galaxy, the Milky Way, is about
100,000 light years across and 3000 light years deep. When you
place your planet, it could orbit a star somewhere in the galaxy,
perhaps between 100 and 70,000 light years from earth. There
are over a hundred billion stars in our galaxy, so you have plenty
of choice! Our own sun is about 30,000 light years from the center
of the Milky Way galaxy. The picture above is a spiral galaxy
like our own. These galaxies are disk-shaped, and thicker in
Galaxies, although surrounded
by a lot of empty space, are found in clusters. Between the clusters
there are enormous stretches of emptiness. The Andromeda Galaxy
is 2 million light years away. The M105 Galaxy is 38 million
light years away. The Cartwheel Galaxy is 500 million light years
away. Abell 2256, a collection of more than 500 galaxies, is
a billion light years away. Your world might be located in a
different galaxy. Again, you have plenty of choices!
We do not know how large the
universe is, as our telescopes cannot see out to the edge of
it -- if there is an edge. The Hubble Telescope has yielded images
of galaxies believed to be 10 billion light years away.
Astronomers hope to learn more about the development of the universe
by studying these pictures.
Scientists assume that wherever
there is matter there will be gravity, the same elements as we
see on earth, and the same physical laws. However, there are
still many surprises in space: beautiful, glowing clouds of stellar
dust, puzzling geology, planets glimpsed in orbit around other
stars. Now that we are able to put telescopes above our planet's
atmosphere, new and exciting information is being uncovered.
© 1998, 2003.
Elizabeth Anne Viau. All rights reserved. This material
may be used by individuals for instructional purposes but not
sold. Please inform the author if you use it at firstname.lastname@example.org.