How Big Is Space Anyway?

"Space," Douglas Adams says in the Hitchhiker's Guide to the Galaxy, "is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space." Seriously! It's tough to grasp how big space really is. Even NASA modifies their artwork to get things to fit on the screen, but movies and TV shows tend to be the worst offenders. To paraphrase my hero Phil Plait, spaceships travel at the speed of plot.

So, to bring back the majesty -- the amazing, mind boggling hugeness -- of space, here's a little primer on how big things really are in space, complete with examples of how to demonstrate these scales at home with your kids. And for those of you that don’t have kids, this is a great opportunity to geek out with your friends and learn about space at the same time.

Let's begin with something small: our home planet, The Earth. As always, size is relative. Earth is the largest rocky body in our solar system. (Venus is a smidge smaller, and Mars is just a little bit more that half the size of the Earth.) The gas giants -- Jupiter, Saturn, Neptune, and Uranus -- are much larger, and everything in our system is dwarfed by our favorite star, the Sun.

Modeling The Sun And planets

The photo above gives you an idea of relative size (though not distance.) Now for the bit that you can do at home with your kids: (And if you don’t have kids, try it anyway! Building models really helps show things in perspective.)

You’ll need a ping pong ball or a small Styrofoam ball about 1-1/4 inches in diameter. (You can also draw a 1-1/4 inch circle on paper, but a ping pong ball will look a little better.) Whatever you use, we’ll call it a "model." You'll also need a 15' long tape measure.

To get a feel for how big the Earth is in comparison to the Sun, we’ll use the model to represent Earth. The Earth is 12,750 km in diameter, so our scale will be 1" equals 10,000 km -- very close to our 1-1/4" model. The Sun is about 1,390,000 km in diameter or about 139 inches -- 11' 7". Place the model on the floor, stretch out the tape measure to the 11’ 7” mark, and ponder our insignificance.

So how big is a spaceship compared to our Earth? That's a great question! Answer: You'd need a microscope to see the International space station at this scale.

Let's try one more adventure: representing the distance of the Earth to the sun. The distance is 149,600,000 km, also known as one Astronomical Unit (AU). To get this to fit in your living room we're going to have to change scales -- one inch will now equal 1,000,000 km. (You can say that bit in a Dr. Evil voice if you want.) What does that get us? Well, the Sun will be about 1-1/3" in diameter or just a little bit bigger than our model, so we can still use it. (Picky people can draw a new model on another sheet of paper.)

How big is the earth at this scale? About the size of a grain of sand. If you don’t want to play with sand, draw a very small dot on some paper. Place the grain of sand 12' 5-1/2" away from the Sun model. Now step back so you can take it all in. You're looking at a distance that takes light eight minutes to travel. The nearest star is four light YEARS away.

Humble yet?