SPA News Circular 202 - March 1998
"CCDs capture lunar craters "
Section activity continues to be good, with a very impressive standard of lunar observations. With his 125mm refractor Grahame Wheatley (Long Eaton, Nottingham) makes his detailed studies of the lunar surface. Grahame's latest superb drawings include Plato (6 Jan); Aristarchus area (9 Jan); Messier and Messier A / Theophilus (both 2 Feb); Plinius and rille (2 and 3 Feb); Ariadaeus Rille and Julius Caesar (3 Feb); Ptolemaeus chain (4 Feb); Gassendi (7 Feb); Vendelinus (13-14 Feb).
John Coates (Burnley) observes with a CCD camera attached to his driven 300 mm reflector. John continues to make detailed studies based on these video images. His latest have included:- Montes Harbinger and Prinz (9 Nov 1997); Burg / Theaetetus / Horrocks / hills north of Cassini (all 5 Jan 1998); Mason and Plana / Grove / Burg / Posidonius A / Plinius / Daniell / le Monnier (2 Feb); Montes Spitzbergensis / Archimedes A / Carlini D (both 5 Feb); Steinheil and Watt, noting distinct shadow banding on Watt's inner eastern wall (14 Feb).
John's observations of Prinz and le Monnier are featured above. Both are good examples of lunar craters whose walls were breached and floors covered with lava flows. They are not "ghost craters", a term used to describe features almost completely buried and visible only when close to the Moon's terminator. It is thought that the volcanic activity that partially covered Prinz and le Monnier took place around 3,500 million years ago (large scale lunar vulcanism ceased around 500 million years later). In le Monnier's case, the lava plain of Mare Serenitatis displays evidence, in the form of low ridges, of the crater's buried western wall. These ridges are only apparent when the sun illuminates the feature at a low angle. Because le Monnier resides partly within Mare Serenitatis' mountain border, at least its eastern flank was in no danger of being obliterated. But Prinz, alone on the relatively flat Oceanus Procellarum, has been more completely covered with lava so that only a narrow crescent of its rim may be discerned, rising about 1,000 metres above the surrounding plain. The Harbinger Mountains northeast of Prinz rise over 2,000 metres. To give some idea of scale, the cluster of peaks that makes up the Harbinger mountains appears from above about the same size and shape as the Inner Hebridean islands of Coll and Tiree.
I have had pleasing lunar results with my new CCD camera (an "everyday"CCD camera, not a fancy astronomical instrument) using eyepiece projection. I have attempted to photograph features near the terminator at a magnification of x200, courtesy of a spell of great nights in February. It is tempting to allow CCD photography to take over the time normally spent making an observational drawing. With a CCD you can take lots of images in a relatively short space of time, and you can take advantage of short breaks in the clouds. Take enough pictures and you're bound to obtain some decent ones! An observational drawing might take anythirig up to an hour or more to make, but the eye remains superior to the CCD when discerning fine lunar detail (using the same telescope). Typical of my initial results is an image capturing the crater-crowded lunar southern uplands. My own most recent lunar drawings have included Mount Pico (using a 250 mm reflector, 14 Jan) and Bilharz (14 Feb).
