The western portion of the Palus Epidemiarum

Although the Ramsden rille system was not on my observing list, the exceptional opportunity presented on 1989 January 17 as regards the seeing quality, was one not to be missed.

Shadow lengths are depicted as seen at the commencement but by the close of the observation – some two hours later – they had shortened considerably. Fine or shallow rilles which lie along, or present only a slight angle to the direction of the incident light, are not normally easy to discern owing to the lack of appreciable shadow, especially under poor or mediocre seeing. One indication of the quality of definition on this occasion was the distinctness with which the E–W rille north of the small crater Marth could be seen.

The number, identity and course of the rilles depicted show differences in some instances with those on published charts but it should be pointed out that the latter show disagreement among themselves if examined! Interested observers may, therefore, care to check what can be seen in the telescope against what is recorded here and elsewhere, always bearing in mind that in observational astronomy it is a recognised fact that everyone sees in his own way!

The crater Marth, 3.8 miles in diameter is, despite its size, a most interesting object in having a complete inner ring which is concentric to, and almost exactly half the diameter of the outer wall.