General Meeting March 2005
Photographing the Lunar 100
Guest Speakers: Arthur E Coombs and John W Robinson
Is the pace of our lifestyle increasing? Or is our attention span (the ability for an object or an idea to hold our attention) shrinking? I am old enough to remember the times when it was considered high fashion to have the Top Ten in music, on radio or cinema, and the two best-sellers in books promoted as an achievement. Now it seems 100 is all the rage; be it ‘the world’s one hundred most influential people’ of the current Time magazine, Best-Loved Recipes, the Messier 100 Club or, as now in Wood’s Lunar 100, a long list of visible objects and features of the moon. In April 2004 author Charles A. Wood set out a list of 100 notable targets on the moon in his Sky and Telescope article. A lunar equivalent of the famed Messier and Caldwell lists of deep-sky denizens. Most of these objects were selected to illustrate the geological history of the moon, and some are significant from the standpoint of man's exploration of the moon. Most require some planning to observe in terms of timing the observation to take advantage of favourable illumination near the terminator (the line where light and dark meets on the face of the moon). Some features near the edge also require timing with respect to the libration of the moon. A few of the objects are so small that they challenge our ability to see detail from the surface of the Earth due to our distance and our atmosphere. The list is arranged in order of easiest to most difficult to observe.
Our Moon is the most fascinating place in the universe, writes Charles A Wood in his book ‘The Modern Moon’, at least as viewed from the Earth. Its pristine surface bears witness to 4.5 billion years of impact cratering, volcanism and tectonism. Haunted by poets, looked upon by youngsters in love, studied intensely by astronomers for four centuries, examined by geologists for the last 50 years, walked upon by twelve humans, this is Earth's only natural satellite, the Moon. Familiar to all of us, but a mystery nevertheless. It is the only place off-Earth that humans have visited, and it is the most likely first destination for an off-world colony. Arthur and John, who completed the monumental task of photographing all of Wood’s Lunar 100 features in early December 2004 have been acknowledged by Charles Wood as, almost certainly, the first in the world to succeed in doing so.
John Robinson, on hand of a comprehensive PowerPoint sequence, led us through the lunar facts: diameter 3,476km, mass 1/80 of Earth, average distance from us 384,400km, Sidereal and Synoptic months are 27.32 days and 29.53 days respectively. The eccentricity of the moon’s orbit allows us to see some 59% of its surface. Understanding the crater-marked surface of the Moon requires a time scale that includes the geologic and astronomical processes that have shaped its varied features. The Pre-Nectarian Period began 4.6 billion years ago when the moon was formed. The Procellarum basin was soon formed (about 4.3 billion years ago) followed by the Tranquillitatis, Fecunditatis and Nubium basins. The Nectarian Period began 3.9 billion years ago when the Nectaris basin was formed and soon followed by the Humboldtianum, Humorum, Crisium and Serenitatis basins. The Imbrian Period began 3.8 billion years ago when the Imbrium basin was formed followed by the Orientale basin, which in turn was followed by great lava flows that filled the Tranquillitatis, Fecunditatis and Crisium basins 3.5 billion years ago with layer upon layer of "runny" basaltic lava. A second lava flow period seems to have followed which flooded the Procellarum and Imbrium basins. Large-scale volcanism and high impact frequency dwindled significantly by 3 billion years ago and was seemingly followed by a quiescent period of 2 billion years. The Copernican Period began with the formation of the crater Copernicus some 900 million years ago. There has been no significant volcanism nor major impacts to speak of since. The various visible surface features are loosely segregated into (and defined as) Maria or Basins, Highlands, Craters and Peaks, Rilles and Ridges, Wrinkles and Rays, Domes and Masoons.
Arthur Coombs then showed us a series of stunning pictures from their Lunar 100 collection, some of which had involved the processing and stacking of as many as 300 photos to bring out the fine details of the listed feature. There were fantastic shots of well-known moon features as well as obscure new landmarks, such as the objects named after the first three men on the moon and sites at the edge of the disc that were extremely difficult to catch and photograph. The project took nine month to complete and had involved experimentation with magnification, with seeing conditions, with telescopes and cameras and with computer programs.
And some helpful hints for budding Lunar 100 champions? Be aware that when looking at the Moon through binoculars or a telescope the angle of the Sun's rays striking the surface is most critical in creating shadows – the presence or absence of which is vital to the proper perception and interpretation of any feature under scrutiny. The human eye has the curious tendency to use shading and shadow as a means to recognise a three dimensional shape in a flat, two-dimensional picture. Our brain instinctively assumes that light comes from up above. So, if the shadow of a circular feature in the photo is at its bottom (the side closest to us) then the feature will be seen as a hill rising above the landscape, and conversely, if the shadow is in the top half of the circle it must be a crater. Next, the shape of an object is highly important to its identification. And the third most important focus should be on the grey tones, which establish an object's texture. Just keeping these principles in mind will help make you an artful observer capable of really enjoying the scenery.
Appreciating the enormous amount of work that Arthur and John have had to put into this project, a saying accredited to Alfonso X of Castile, a medieval patron of astronomy, A.D. 1221-1284 comes to mind: “If the Lord Almighty had consulted me before embarking on the Creation, I would have recommended something simpler.”