|MadSci Network: Astronomy|
First of all, sorry for taking a while to answer. Good question! Light is the fastest thing in the universe, but it does travel at a definite speed - it takes time to get places. In fact, the speed of light is about 300,000 kilometers every single second. At that speed, light from the Sun takes 8 minutes to reach us. This is a problem when we try and control spaceprobes - any signal sent to Jupiter, for example, would take several hours to reach the probe - not much good if you want to send an urgent signal. The same applies to light from the stars - the light from Alpha Centuri left the star about 4 years ago so you are seeing the star as it was then. Any aliens on Alpha Centuri who happen to be looking at the Earth will see it as it was in 1997! If we look at the furthest galaxies, we can be looking many billions of years back in time! Light travels much faster than sound. For example if you stood beneath Big Ben in London with a radio, you would actually hear the bongs from the radio first, before you heard them directly. This is because the radio waves travel at the speed of light, and so reach you before the sound does, even though they have to travel much further (to a studio and back)
Try the links in the MadSci Library for more information on Astronomy.