The stars are so far away from us that astronomers do not normal measurements such as kilometers or miles. Instead, they have invented a unit called the light year. This is the distance traveled in one year by a beam of light, which moves at the fastest speed in the Universe, 300,000 km (187,000 miles) per second. A light year equals 9.5 million million km (6 million million miles). The nearest star, Alpha Centauri, lies 4.3 light away, or 40 million million km (26 million million miles). That’s 300,000 times further away from us than the Sun. The Space Shuttle, travelling at top speed, would take about 160,000 years to reach Alpha Centauri. Some of the stars you can see at night are so distant that their light has taken hundreds or even thousands of years to get here.