Light travels very fast.It moves at speed of 300,000kilometers a second.Light reaches us from the moon in less than a second and a half.The moon is about 382,000kilometers away.Light from the sun reaches us in 8.5minutes.The sun is about 149,840,000kilometers from the earth.The other stars farther away than the sun.Light from the nearest star reaches us in about four years.When you look at a star,you do not see its present condition.You see a star as it is now.We see it as it was long ago;perhaps hundreds of thousands of years ago.Astronomers (天文学家)watch the stars through big telescopes.The world’s biggest telescope is in Russia.The next biggest is in the United States.With these great telescopes astronomers can see stars and other things very far away.Some of these things are not only stars.They are great groups of stars