The Guiding Star

Polaris, the North Star, can be seen at every hour, every night of the year. Itıs easy to find from the Big Dipper (the two end stars of the Big Dipper's bowl point directly at Polaris.) It is "the ever fixed star," but certainly not "the brightest star that shines," as the song claims. In fact, it is a pretty ordinary star in all respects, except that it is always in the same position. That's what makes it special.

The axis of the Earth is like a giant knitting needle passing through the poles; the Earth rotates around this axis once a day. The axis always points in the same direction: towards the star Polaris. So Polaris always appears in the same place in the sky, while all the other stars rotate around it. It is just where it appears in the sky that makes it so important to navigators.

If we were at the North Pole, the axis of the Earth would point straight up, and the North Star would be directly overhead.

As we move away from the North Pole, Polaris drops in the sky (there's nowhere else for it to go.) How far it is from overhead tells us how far we are from the North Pole.

Here in Vermont, Polaris is just about halfway between the horizon and the zenith, and that's where we are on the Earth, halfway between the equator and the North Pole (there's a sign on Rt. 91 that says just that.)

Centuries ago about all navigators had to rely on was the position of the North Star. That told them how far they were from the North Pole, and so they would know how far they were from the equator - their latitude.

But that was only half the story. What about their longitude -- how far east or west they were from, say Athens? Well, they couldn't know that until good clocks were developed, sometime in the eighteenth century. That's what made navigation so interesting.

All early navigators, even Columbus, could do was sail to the correct latitude and then go east or west until they bumped into something. If they were lucky it was what they were looking for. It wasn't, for Columbus, but it was good enough. Both for him and for us.

(07/25/07)