# Precession of the Sun's rotation axis

1. Jul 27, 2010

### natski

Hi all,

As the sun is an oblate spheroid and is rotating, should not the axis of rotation be precessing, much like the Earth does?

What is the axial tilt angle and what is the precession period in years? Also, what is the amplitude and period of the nutation? Are there are equations for estimating these values for different configurations?

Thanks,
Natski

2. Jul 28, 2010

### D H

Staff Emeritus
That the Earth's rotational axis undergoes a slow precession results from tidal (gravity gradient) torques caused largely by the Moon and the Sun. There would be no precession if the Earth was spherical or if the axial tilt with respect to the orbital angular momentum vectors was zero.

The Sun is very nearly spherical (it's flattening is about 10-6), is nearly aligned with the ecliptic (the Sun's axial tilt with respect to Jupiter's orbit is about 6 degrees), it has a relatively small rotation rate (one rev per 25.5 days), and the bodies that might cause a precession are far from the Sun (gravity gradient torque is an inverse cube relationship). All of these factors means that the Sun's precession rate will be exceedingly small.

3. Jul 28, 2010

### natski

Thank-you for your detailed response D H. There are, however, plenty of stars which are fast rotators and therefore would be flattened considerably with a nearby companion M-dwarf (for example) and could exhibit much faster precession and so the question remains. What formulas can one use to estimate this precession rate?