When we started with astronomy—about 6 months ago—we did things backwards. Let me explain: we jumped right into using a telescope, knowing some astrophysics but not really knowing the night sky; basically, we started building the house from the roof down. But what’s done is done. So last week we started a course at USC, and here we are again, almost dreading the exam.
Still, we’ve learned quite a bit. For example—and even though it’s obvious—I can now explain why the North Star (Polaris) always stays fixed in the sky. This star, located in the constellation Ursa Minor, is in a very special spot, right above Earth’s axis of rotation. To picture it: if space were a record spinning on a turntable, Polaris would be right in the center—always still while the other stars move around us. It’s not the brightest, biggest, or closest star, but in the Northern Hemisphere, it’s always due north. (Though it hasn’t always been, and won’t always be, since Earth’s axis shifts over time.)
To find it, look for the Big Dipper (the one shaped like a ladle) and, on the opposite side, Cassiopeia (shaped like an M or W). Polaris is five times the distance up from the end of the Big Dipper’s bowl (opposite the handle), or if you extend the middle point of Cassiopeia upward (toward the Big Dipper), it’s halfway there.