Moon tour

How to find the most dramatic cliff on the face of the Moon

If you have a small telescope, or a powerful pair of binoculars, and look to the lower left of the great triple-crater chain of Ptolemaeus, Alphonsus and Arzachel you will see - depending on the time of the month - either a short, dark line or a short, bright line. Moon atlases and phone apps identify it as ‘Rupes Recta’, and to be honest it doesn’t look like much at first glance, nothing more than a dark pencil line or a white chalk scratch drawn on the Moon’s round, grey face. But Rupes Recta has another name, and it is one of the most famous and beloved features on the whole of the Moon. It’s known as the ‘Straight Wall’. It’s not actually a wall. It is an enormous scarp, a region where part of the Moon’s surface dropped dramatically away, leaving a steep cliff behind.