A Simplified Method to Determine the Coordinates of Albedo Features on Visible Disk of a Spherical Planet under Different Illumination Conditions

Abstract

A simplified method for the determination of planetocentric coordinates of albedo features on visible disk of a spherical planet under different illumination conditions is offered. The method is precise and is intended for handling images of the planets obtained on ground-based and near-earth telescopic observations. The position of a feature on the image of a planet is determined by means of rectangular coordinates in the transverse orthographic projection, independently of planetocentric declination of the Earth. To determine point positions on the illuminated part of the visible disk of a planet, we applied an auxiliary coordinate system connected with equator of intensity that allowed to exclude the influence of the planet’s phase and to make transition to the planetocentric coordinate system. The method is tested on images of Mercury and Mars.