Looking at the night sky is like looking back in time because light takes years to reach your eyes.

Light travels at about 300,000 kilometers per second. This is the fastest speed possible in the universe. Even at this speed, light needs time to cross the huge distances in space. This delay is called lookback time.The Sun is about 150 million kilometers away from Earth. Its light takes 8 minutes and 20 seconds to reach us. If the Sun stopped shining, we would not know for over 8 minutes. Other stars are much further away than the Sun.Proxima Centauri is the closest star system to our Sun. It is 4.24 light-years away. This means the light you see from it tonight started its journey over four years ago. Some stars you see are hundreds or thousands of light-years away.The star Betelgeuse is about 642 light-years from Earth. If it exploded today, people on Earth would not see the explosion for 642 years. We see the North Star, Polaris, as it looked in the year 1591. The further away an object is, the further back in time we see it.The Andromeda Galaxy is 2.5 million light-years away. We see it as it looked before modern humans existed. Astronomers use powerful telescopes to look at even more distant light. They can see galaxies as they looked 13 billion years ago, shortly after the universe began.