Make your own precession calculator

Print out the pieces

The image below is the base of the calculator. Print this image on thin card.

Precession calculator base

Figure 1a. Precession calculator base

The image below is the Solstice/equinox marker wheel. Print this image on to thin card and cut round the dotted line.

Solstice/equinox wheel.

Figure 1b. Solstice/equinox wheel.

Fix the center of the wheel to the center of the base with a stud of some kind. You could paste the base onto a cork tile and fix the wheel with a drawing pin.

Go down to any sky

As any Pharaoh of ancient Egypt could tell you, finding the sky for any era is a cinch.

  1. Set the SE (spring equinox) arrow to the 2005AD mark in Pisces. That puts you at today's time.
  2. The direction of precession is shown by the arrows on the wheel. Move the SE arrow forward to the end of the next segment, Aquarius, and you'll see the spring equinox constellation (Aquarius moving into Capricorn) for about the year 4200AD. (It takes about 2160 years to traverse each segment.)
  3. Move the SE arrow back a whole segment and you'll see the spring equinox constellation for about the 1st century BC (Aries moving into Pisces).

The other markers give you the other equinox and solstice constellations. For example, if the spring equinox marker is set to Leo, (about 10-12000 years ago), then the autumn equinox would be Aquarius, the summer solstice would be Taurus, the winter solstice would be Scorpio.