A digital analysis of sunspot areas

Full-disk white light images of the Sun have been digitized, calibrated, and examined to determine objective sunspot areas for the early part of the operation of the Solar Maximum Mission satellite. We find that published sunspot areas determined from synoptic programs compare favorably with our digital areas. The mean residual between published areas and our digital areas is approximately 80 millionths of a hemisphere. The largest residual found is 642 millionths on April 1980 for Hale No. 16752.