The Star Compass

The Polynesians developed a star compass. Look round your horizon and note the position where stars rise. These positions become your compass points. With luck you will be able to find a convoy of stars popping up one after the other at each compass point so that as one star climbs too high to use for direction, the next comes over the horizon.

Knowing the declination of stars we can produce a star compass in minutes. Take Betelgeuse, a bright star in the constellation of Orion. It has a declination of 7o N. From the equator, Betelgeuse rises on a bearing of 083o. Repeat this for stars around the horizon and you have your star compass where all bearings are true, and deviation or variation non-existent.

It sounds too good to be true. It is. For it works only as long as you stay within about 10o of the equator where the change in a star's bearing is only about six or seven degrees. Further north or south the bearing changes more quickly. Soon your star compass is useless. At higher latitudes you must make a new one every couple of degrees of latitude, and the increasing number of circumpolar stars means fewer stars to choose from.

0 0

Post a comment