You have to be a really big thinker to imagine the size of the Universe. It's so big that light from the most distant galaxies takes over 10 billion years just to reach us on Earth! That's twice as long as Earth's been around. Everything we've ever observed in space is part of our Universe. We don't know what's beyond it or if there are other Universes out there.

Image credits: main image, The image of the universe, © American Museum of Natural History and the National Center for Supercomputing Applications, 1999; quote, © AMNH.