After my last post about the Earth and Sun, I thought I’d post something I’d previously written about the scale of the Universe. As I said, this stuff fascinates me and boggles my mind. I love the feeling of utter incomprehension 🙂

Imagine a football field. It’s the beginning of the season, so the grass is looking beautiful. It’s been recently cut and you can see the alternating stripes going one way then the other. The smell of the grass is wonderful. Imagine walking barefoot from one end of the field to the other, feeling that wonderful sensation of soft grass under your feet. How many blades of grass do you think there are on that field? Lots. In fact, in a typical field there are about 250,000,000 blades of grass, a quarter of a billion. I want an area with 200,000,000,000 blades of grass, and for that we need to put together 800 football fields. Now, 800 football fields is going to take a long time to walk along, so let’s put them side to side rather than end to end, and let’s imagine walking across them all.

After a while we are in the middle of the 347th field. Let’s stop here for a moment. I want you to take out a small jar of yellow paint that you are carrying, bend down, and paint just one blade of grass yellow. After you have done that, continue walking across the remaining 453 football fields. Okay, what was the point of that?”

What we have just done is look at the number of stars in our galaxy—about 200,000,000,000—and we’ve painted one blade of grass corresponding to our sun. There’s nothing special about 347 though—I just wanted you to have walked a long way, and still have a long way to walk. And this is only a fraction of the universe.

There are estimated to be over 100,000,000,000 galaxies in the universe—maybe 125,000,000,000—and some theories in physics say there may be multiple universes.

If we want to look at our sun relative to all the stars in our universe, imagine grass covering the entire surface of the Earth—land, lakes, seas and oceans—and remember that more than two thirds of the surface of the Earth is water. All of America is covered with grass, as is Europe and all of Africa, all of Asia. The Atlantic Ocean is covered, as is the Pacific Ocean. The whole surface of the Earth is covered with grass. Each blade of grass represents one star, and again, our sun is one blade of grass painted yellow.

Douglas Adams, the author of The Hitchhiker’s Guide to the Galaxy, said it well when he wrote, “Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the drug store, but that’s just peanuts to space.”

[Update: Since my original writing about the football fields and grass covered planets, scientists have revised the galaxy count, and now believe there are over 2 trillion – 2,000,000,000,000 galaxies in the universe. Which would mean grass completely covering 20 Earth size planets, and our Sun a single blade of grass on one of those 20 planets.]

Links and Other Clicks

Scientists now estimate that the Universe contains more than two trillion galaxies.

The book where I originally wrote the stuff above.

The Hitchhiker’s Guide to the Galaxy gave us the answer to “what is 6 times 7”. Oh, wait, it was a different question.