Calculating Differential Rotation
For observed sunspots, the differential rotation can be calculated as:
where is the rotation rate at the equator, and is the difference in angular velocity between pole and equator, called the strength of the rotational shear. is the heliographic latitude, measured from the equator.
- The reciprocal of the rotational shear is the lap time, i.e. the time it takes for the equator to do a full lap more than the poles.
- The relative differential rotation rate is the ratio of the rotational shear to the equatorial velocity:
- The Doppler rotation rate in the Sun (measured from Doppler-shifted absorption lines), can be approximated as:
where θ is the co-latitude (measured from the poles).
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