Cosmic Perspectives from Amid the Stars:
Astronomy Blog

You might have heard before that the nearest star is 4.24 light-years from Earth. Or that the closest galaxy is 2.5 million light-years from the Milky Way. Or even that the most distant observed objects are 33.8 billion light-years away. But how do we measure these distances in space? After all, there’s no such thing as a cosmic ruler. That’s where the cosmic distance ladder comes in.

There is an estimated septillion stars in the observable universe (that’s a one followed by 24 zeroes). They’re everywhere you look and come in all sorts of varieties. Every star is unique, but they all follow a similar life cycle. A star is a ball of gas, usually hydrogen and helium, that is so dense, it can fuse that hydrogen into heavier elements, creating energy. Depending on its size and rate of fusion, a star can live anywhere from a few million years to trillions of

When you look up at the night sky, you’re not only looking out into space, but also back in time. You’re seeing stars that exist hundreds to thousands of light-years away, and that means you’re looking back hundreds to thousands of years into the past.