Cosmic Perspectives from Amid the Stars:
Astronomy Blog

The true size of the universe boggles the mind. It’s so large that it is simply impossible to truly grasp its size. Even light, which travels faster than anything else, takes time to travel through space. For light, it’s eight minutes from the Sun to Earth, four years to the closest star, and a hundred thousand years to cross the Milky Way. To truly appreciate these vast distances, a scale model is necessary.

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.

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.