It's very far from the Earth to our sun. If you took the fastest jet we have, it would still take you over six years to get there and back again. The other kids in your class would be gone to different schools by the time you got back. Six years is a long time, but that's nothing compared to how far it is to the next galaxy, or group of stars. If you tried to pop over there, the planet Earth might be gone by the time you get back.
It's so far to the next group of stars that we have to throw away everything that we know about distances to understand it. If someone asked you how far it is from here to Australia, would you tell her how far it is in inches? Of course not! You could use inches to give her an idea, though. Relative distance
is how far it is between two places by comparing it to the distance between two other places. Look at a globe. It's fourteen inches from the US to Australia. If every inch is about five hundred miles, then on the real Earth it's 7,000 miles away. We can use that same trick for space.
OK, but how far is it to my best friend's house?
You may have been on a road sometime where there wasn't much going on. There are no stores, no houses, no lights. These are the places that take us from one town to the next. Space has something just like that. Intergalactic
means the spaces that are in between galaxies. Just like those empty roads, there is not a lot going on there. Try not to get stuck on an intergalactic road. It will be very hard to hitchhike a ride from a passing asteroid.
It's been a long time since we saw anyone else on this highway. Are you sure we're going in the right direction?
So if the space between us and the sun takes years to cross and the space between our sun and the next star is thousands of times that and the space to the next galaxies is thousands of times that . . . just how far does it all go? The universe
is the word we use to talk about everything we know of. At this point, we believe it would take around ten billion years for light, the fastest thing ever, to move from one end to the other. You are a bit of dust on a bit of dust. But still a very special bit of dust, I am sure.
The universe; 1.6 million galaxies and counting.
The size of everything is not easy to figure out. We have to throw away everything we know about space on Earth and come up with new ways to think about it. We use things we know about down here to talk about those long stretches between the galaxies, which are very, very big. When it comes to everything in space, you may only be a bit of dust, but by reading this you just fit the universe inside your brain.
Khan Academy. "Intergalactic Scale" Khan Academy, 2012. <https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/scale-earth-galaxy-tutorial/v/intergalactic-scale>
Universe Today. "Intergalactic Space" Universe Today, 2009. <http://www.universetoday.com/30280/intergalactic-space/>
NASA. "How Big Is Our Universe?" NASA, 2004. <http://www.nasa.gov/audience/foreducators/5-8/features/F_How_Big_is_Our_Universe.html>