Everything Changes

As the stars wheel overhead, one star stays fixed all night -- the North (or Pole) Star. Right now, that star is Polaris. Polaris will be the Pole for our entire lifetimes. But not forever: it wasn't in the distant past nor will it be in the far future.

The stars appear to move across the sky every night because the Earth itself, with all of us on it, is turning. Right now, the axis of the Earth points to the star Polaris: that's why Polaris stays fixed while the other stars wheel around it.

But, like a spinning top, the axis of the Earth moves slowly, pointing first to one star and then to another. In our lifetimes it won't move very much, but over the course of human history, it will.

Ten thousand years from now it will point to Vega, and that will be the Pole Star then. Five thousand years ago this axis pointed to Thuban, in Draco the dragon. Thuban is a dim star midway between the end of the Little Dipper and the handle of the Big Dipper. And there lies a tale about the transience of human life:

In ancient Egypt, five thousand years ago, the Pharaoh Khufu died. The Great Pyramid was built at Gizeh to house his last remains and a passage to the outside was made aligned with Thuban. All night, every night, the light from that star would shine down the passage. This was thought to be a suitable symbol for his eternal life in the nether world. Alas! The axis of the Earth moved; Thuban was no longer the Pole Star. Only empty sky shows through the passage now.

Nothing that we can see lasts forever, not even the stars.

(03/13/07)