STARS AND CONSTELLATIONS. On a clear night, away from the lights of a town, you can see about 2,000 stars with the naked eye.
A telescope can reveal millions. 
Like the Sun and the Moon, the stars appear to move slowly accross the sky but in fact it is we who are moving as the Earth rotates.
	CONSTELLATIONS. In ancient times, people were reminded of the outlines of animals and gods in the sky and gave their names to the groups of stars that they saw. 
These groups are called constellations.
	These are not in fact actual groups of stars that are near each other in space - some may be near us while others are far away. 
But dividing the sky into these recognizable patterns helps ua to map the sky.
	GALAXIES. Through a powerful telescope, vast groups of stars called galaxies can be seen. 
Our Sun in fact belongs to a galaxy containing about 100,000 million other stars; when we look at the Milky Way, we are looking at our own Galaxy. 
Millions of other galaxies are scattered throughout space.
	Many are shaped in a flat disc like our Galaxy, and made up of spiral arms of stars reaching out from a central hub of stars. 
Our Galaxy is retailing slowly and the Solar System, situated along one of the spiral arms near the edge of the Galaxy, makes one circuit every 225 million years.
	MEASURING DISTANCES. Distances are so vastin astronomy that they are measured in light year - the distance light travels in a year. One light year is nearly 9,5 million kilometres and our Galaxy is 100,000 light years across.
	THE LIFE OF A STAR. Stars form as hydrogen comes together in clouds that contact with gravity and eventually begin to burn. 
Many stars burn for millions of years and then expand into a red giant star before contracting to a cold dwarf star, their fuel used up. 
But some stare end their lives in a gigantic explosion. 
An exploding star is called a supernova and is very bright indeed.