Stonyhurst Discs and the Orientation of the Surface of the Sun
Locations on the solar surface are defined using three parameters:
The rotational axis of the Sun is inclined at 7.25° to the normal to the plane of the ecliptic. (By way of comparison, this is considerably less than the Earth, for which the rotational axis of the planet subtends an angle of 23½° to the normal to the ecliptic). As a result, the Sun’s axis appears to rock both left and right and back and forth over the course of a year.
The current longitude measurement system was created by Richard Carrington (1826-1875) on 1853 November 09. The value of L0 falls from 360° to 0° over the course of 27.2753 days.
The animation below uses data at five day intervals from the BAA Handbook for 2011. It was created by animating a set of Stonyhurst Discs (represented by .pdf files).
Bill Barton, FRAS