If you have an astronomical telescope with no erecting or right angle prism, the image of the Sun will be inverted and north will 90 o clockwize from west on the drawing. For each sunspot of interest measure the distance from the center, r position angle, pa, of the radius line from North. The position angle should be measured as positive in the direction for North to East. The values of the parameters B o , P, L o depend only on the date and time. Radius of Solar Image Use the same units for all linear measurements.
Angles are all in degrees.