Revisiting the 1963 'Aristarchus events'

A Transient Lunar Phenomenon (TLP) is a short-lived unexplained change in the normal appearance of a localised area of the Moon, and can include coloured and colourless glows, grey shadows, brightness changes and obscuration of detail on the lunar surface. One long standing debate in lunar science concerns whether these phenomena are real physical events in the vicinity of the lunar surface, or just observing artefacts or misinterpretations. During a couple of nights in late 1963, experienced observers at Lowell Observatory, Flagstaff, Arizona made two of the most famous observations of TLP, known as 'The 1963 Aristarchus events'. After five decades we re-examine the background and reliability of these observations and discuss possible terrestrial and lunar explanations for what was seen.