A light year is the distance light travels through empty space in the course of one year.

1 light year = 9.461 x 10 ¹² km = 5.878 x 10 ¹² miles

In order to comprehend the enormity of space, astronomers use a variety of methods to measure the distances between stars and between galaxies.

Our own galaxy, the Milky Way, is around 120 000 light years across and the Sun occupies a position roughly 28 000 light years from the centre. Within the Milky Way, the nearest star to the Sun is Proxima Centauri, which is about 4.4 light years away. But most of our nearest stars are between 100 and 1000 light years away from Earth.

From any given location on Earth it is possible to view around 7000 stars with the naked eye and countless more with a telescope. In all, our galaxy contains over 1 billion stars.

The distance to stars in our galaxy is obtained using a technique called parallax. By identifying certain stellar properties it is then possible to calibrate a distance scale out to our galactic neighbours.

The nearest galactic objects are the Magellanic Clouds. The Large Magellanic Cloud is 170 000 light years away, while the Small Magellanic Cloud is at a distance of 210 000 light years. The next nearest galaxy is Andromeda (M31 in the Messier catalogue), at a distance of 2.3 million light years.

Galaxies are usually part of a larger group of galaxies. The group of galaxies that includes the Milky Way and Andromeda, plus several other smaller companion galaxies, is known as the Local Group. The other galaxies in the Local Group are between 80 000 to three million light years away from the Milky Way.

The next nearest rich cluster of galaxies, the Virgo cluster, is around 60 million light years away. It is believed that the Milky Way-Andromeda cluster is part of an even bigger supercluster along with Virgo-Coma cluster.

	Stellar Clusters & Constellations
	Stellar Motions