Bright-dark asymmetry in solar granulation

Abstract

Although a positive print of solar granulation gives the impression of bright irregular areas on a dark background, this impression is highly subjective and depends upon the nature of the photographic process. We developed an objective method for comparing bright and dark features and applied it to 40 000 elements from a granulation photograph. Each element had dimensions of 150 km by 150 km. We found that dark features were fewer in number, larger, and had larger perimeter-to-area ratios than the bright features. The statistical confidence level of our results exceeded 99%. Our results are consistent with the subjective impression that granulation is composed of bright features separated by dark lanes.