I love things that put hard-to-understand concepts in practical perspective. Here's one I ran across while waiting for my wife at the hair dresser the other day. It's about our own galaxy, the Milky Way. Scientists think that there are between 200 and 400 billion stars in the Milky Way.
To get a sense of what that means you can compare it to the grains of salt in that familiar blue and white round carton of Morton's salt. You know the one I'm talking about with that little metal pour spout that flips up. Well it turns out that there are about 15 million grains of salt in one of those cartons.
So if you go out and buy 26,000 of those cartons of salt you will have as many grains of salt as there are stars in the Milky Way galaxy.
And if you wanted to make a one-dimensional model of the Milky Way you'd lay out all those grains of salt on a large piece of black cloth so that each one was seven miles from it's nearest neighbor.
But I don't advise you try this at home. The piece of black cloth would have to be twenty-five times larger than the earth!
That's how big the Milky way is...