The Earth's axis of rotation is not fixed in space; instead, it undergoes a slow, continuous change in direction. This movement is commonly referred to as "Earth's wobble," or more formally, axial precession. This phenomenon affects long-term climate patterns and the location of the celestial poles over thousands of years.

What is Precession?

Precession is the slow shift in the orientation of a rotating body's axis. It can be compared to the slow, circular wobble of a spinning top just before it falls over.

For Earth, this wobble is caused primarily by the gravitational forces exerted by the Sun and the Moon on the Earth's equatorial bulge (the slight swelling around the equator).

The Precessional Cycle

The Earth's axis completes one full wobble cycle approximately every 26,000 years.

Effects of Precession

1. Change in the North Star

Today, the North Celestial Pole points very close to the star Polaris, which is why it is called the North Star. However, due to precession, this will change over time.

• Current North Star: Polaris
• Past North Star: Thuban (around 2600 B.C.)
• Future North Star: Vega (around 14,000 A.D.)

2. Shift in the Position of the Equinoxes

Precession causes the vernal (spring) and autumnal equinoxes to gradually move westward around the ecliptic. This is where the term precession of the equinoxes comes from.

• This shift means that the astrological and astronomical constellations have slowly drifted apart since ancient times.

3. Impact on Climate (Milankovitch Cycles)

Precession is one of the three primary components of the Milankovitch Cycles, which describe how changes in Earth's movement affect solar radiation and are thought to be a major driver of ice ages.

• The change in the direction of the axis determines when in the Earth's orbit the seasons occur. This impacts the severity of the seasons, particularly in the Northern Hemisphere.