How far away is the moon? When the grade schoolers show up at
Perkins Observatory, they invariably ask, “How far away is
that.” Since 650 billion miles doesn’t make a whole lot of sense
to them (or me, quite frankly), the temptation is to say,
“Really, really far away.” Even the distance to the moon — about
a quarter of a million miles — is incomprehensible. One of my
colleagues at Ohio Wesleyan University once said to me, “It’s
easy, just 10 times around Earth.” I replied, “So how many times
have you traveled around Earth, even once?” It helps to go out
and look. You can see the moon from your backyard, and it looks
very obviously close. Binoculars show the craters as small dots
on the moon’s surface. A small telescope shows the craters in
more detail, plus mountain ranges and giant lava fields, to
boot. These details were invisible to humanity before the
invention of the telescope about four centuries ago.
Surprisingly, many of the things we know about the moon, we have
known for a lot longer than that. The