How big is the Earth?

Guy Ottewell, astronomy writer and eccentric polymath, writes a well-regarded annual astronomical calendar. His Astronomical Companion is the best single book I’ve ever read on astronomy. As an inveterate teacher, he also created an exercise called the Thousand Yard Model, in which the size and relative location of the nine planets is made graphically apparent to students. If, it instructs us, the Sun is an eight-inch ball, then the Earth is a peppercorn 26 yards away and Jupiter is a chestnut 132 yards away. The name of the exercise stems from the fact that tiny Pluto is a pinhead a thousand yards away. The resulting exercise gives a visceral sense of the relative emptiness even of so crowded a region of space as our Solar System.

I thought of the peppercorn Earth model because of a nifty visualization I saw this morning on information aesthetics called The Size Of Our World. The graphics are lovely, and while you don’t get a feel for how far apart things are, you get a better sense of relative sizes with their rendered, shaded spheres than you would with flat cartoons. The bodies displayed graduate from planets to larger and larger stars until we are treated to the enormity of mighty Antares (It looks like Mars in the sky, but it’s not; it’s anti-Ares. Get it?). The very best part is the fact that the stars cast shadows on the surface beneath them. You know, I’d bet quite a lot that old Betelgeuse has never ever once in its venerable star life cast a shadow. I would go so far as to suggest that a star with a shadow is going to have some serious self-esteem issues.