Cosmic Perspectives from Amid the Stars:
Astronomy Blog

The universe encompasses everything we know to exist. Time itself only has meaning within the universe. It’s impossible to imagine that the universe may have once not existed at all, and yet, that’s the current consensus among cosmologists. The Big Bang is the most widely accepted theory for how the universe began.

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.