10.7 - Be able to use sunspot data to determine the mean solar rotation period

The Sun is a giant ball of gas and plasma. It does not rotate in the same way that a terrestrial planet like Earth does. It rotates slower at the poles because of its size and structure.

Rotation varies from 25 days at the equator to 36 days at the poles.

Astronomers safely observe the rotation of the Sun by recording the speed of sunspots across the photosphere.



The surface of the Sun rotates in 25 days at the equator and 36 days at the poles


A) An astronomer sees a sunspot travels across the surface at the equator. How long would it take to travel from limb to limb?

B) How long would it take to circle the sun?

A) The Astronomer would see the sunspot travel across the face of the Sun in approx. 12.5 days

B) The rotation of the sun at the Equator is 25 days. Remember it must travel the other side too!