Earth’s Wobble

The precession of the equinoxes

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The Sun and Moon tug on Earth’s equatorial bulge, making its axis precess.
• One full precession takes about 26,000 years (about 50″ per year).
• The pole star changes over millennia: Thuban, then Polaris, later Vega.

Steps

1. A spinning top the size of a planet
2. How fast?
3. Drifting zodiac
4. Precession and ice ages
5. Pole stars through the ages
6. The pole star