Night Watch

When you take a picture of your friends or family, it’s a moment frozen in time — you see everyone and everything in the picture as they appeared at the same instant. A shot of the night sky, on the other hand, is like hundreds or thousands of individual snapshots all pasted together. That’s because you’re seeing every star as it appeared at some point in the past — anywhere from a few years to thousands of years ago.
The light from each star races through space at 670 million miles per hour — faster than anything else in the universe. Yet the gulf between stars is vast — trillions of miles to even the closest of them. So even light takes a long time to travel from one star to another.
As night falls this evening, for example, look in the southwest for Sirius, the brightest star in the night sky. The light you see from the star tonight actually began its journey 8.6 years ago. That means the star is 8.6 light-years away.
Orion is off to its right, marked by the hunter’s three-star belt