North from Polaris

Right now Polaris is less than 1° from the true pole and circles the Pole every 24 hours. Anything that points north to within one degree is fine for helming, but you will need to find the true pole if you are using Polaris for latitude, (see Chapter 16).

8.7 Finding Polaris in a Cloudy Sky Precession of the Equinoxes

Because the earth's axis wobbles, Polaris has not always pointed north. Project this wobble out into space and every 28 500 years it makes one revolution. Stars on or very close to the circumference of this circle take their turn at being the north star. In 8000 years time it will be Deneb's turn.

The earth's wobble also causes the First Point of Aries to slip along the ecliptic. This is called the precession of the equinoxes (shown in Figure 8.8). Since SHA is measured from the First Point of Aries, star declinations also change and every 25 years, star atlases are redrawn.

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