LUNAR SECTION CIRCULAR Vol. 53 No. 1 January 2016 _________________________________________ CHRISTMAS DAY FULL MOON 2015 Maurice Collins' image of a rare Christmas Day Full Moon. The last time this happened was in 1977 and the next won’t be until 2034. FROM THE DIRECTOR The waning gibbous Moon in the period immediately after Full offers spectacular views of sunset over several grand craters near the eastern limb. These include such familiar features as Petavius, Langrenus, Vendelinus and Cleomedes, and all were on display during a brief break in the Sheffield cloud on the morning of 2015 November 28. They may be well studied and frequently imaged, but these craters are always worth another look, and I was reminded that some fifty years ago they were considered part of what Patrick Moore termed ‘the great western chain’ (east was west in those days!). Such apparent ‘chains’ of craters were then regarded by some as evidence of non-random distribution, which in turn pointed to a likely volcanic origin whereby such features formed along lines of crustal weakness (Fig. 1). Fig. 1 Map of major crater ‘chains’ by Patrick Moore. From Survey of the Moon (1963) Of course, we now know that this is not the case and that these features are of impact origin, like the overwhelming majority of craters on the Moon. Moreover, their apparent alignment in chains is merely an effect of foreshortening as we approach the lunar limb. Another argument against a common volcanic origin is that craters such as Petavius, Vendelinus, Cleomedes and Langrenus clearly differ from each other in both morphology and age. Cleomedes is a dark-floored crater perched just within the outer northern ring of the Crisium basin, and it appears to be flooded by similar lavas that comprise the Mare Crisium; Vendelinus is a ruined relic from the pre-Nectarian era whose floor is crossed by bright ejecta that appears to come from the much younger Langrenus. Langrenus itself is a beautiful crater that would be even more spectacular were it more centrally located on the Moon’s disc. With its fine terracing 2 and central peak complex it is similar in general appearance to Copernicus, although it is larger (132 km) and probably older (Fig. 2). It is also the site of one of the more significant TLP reports, by the French astronomer Adouin Dollfus who recorded a series of glows there in 1992. Fig. 2 Langrenus, imaged by Bill Leatherbarrow, 2015 November 28, 03h 34m UT. col. 112.9. 300mm Mak-Cass, ASI224MC camera with IR pass filter. Petavius (177 km) is different again: it is a floor-fracture crater even larger than Langrenus and rather older. Its most distinctive feature is the great rille running from its central peaks to the SW rim, but this rille is only one of several such fractures caused by magma collecting below the surface and doming the crater floor. As it meets the SW terracing the main Petavius rille appears to form a T-junction with another rille circling the inner wall (Fig. 3). 3 Fig. 3 Petavius, imaged by Bill Leatherbarrow, 2015 November 28, 03h 29m UT, col. 112.8. 300mm Mak-Cass, ASI224MC camera with IR pass filter. Observers have often queried the subsequent behaviour of this latter rille, but careful scrutiny using LROC imagery shows that it is connected with the Hase rille system that runs from the SW rim of Petavius to the crater Marinus, with just a few dog-legs and disconnections along its length (Fig. 4). Fig. 4 How the Petavius rille connects to the Hase rille system. Image by NASA/QuickMap. 4 So even these familiar craters throw up interesting insights, and they are well worth revisiting in 2016, for which I wish you clear skies! Finally, I am grateful to Alan Wells and Dave Finnigan for following up my observation of the central peak shadow of Maurolycus in the last issue. I hope we can report further on this in due course. Bill Leatherbarrow ___________________________________________________________ OBSERVATIONS RECEIVED Apart from a sketch of Eratosthenes by Dale Holt, the dearth of visual observations and drawings continues as observers increasingly migrate to the use of high-resolution imaging. However, it should be emphasised again that visual submissions are still welcome. Meanwhile, despite the poor conditions in the UK in November and December excellent images have been received from the following observers: Leo Aerts, Maurice Collins, Dave Finnigan, Clyde Foster, Rik Hill, Alex Houston, Bill Leatherbarrow, Lars Lindhard and Mark Radice. Meanwhile Mike Brown, one of our most experienced imagers, has submitted the following record in support of his view that imaging opportunities seem to be getting fewer and fewer, at least from his observing location in York. It makes depressing reading: ‘I’ve done an analysis of my last six years of Lunar avis captured, with the undermentioned results: 2010 15 sessions 2011 24 sessions 2012 21 sessions 2013 17 sessions 2014 11 sessions 2015 8 sessions I felt the evidence proves a rather large decline in the number of opportunities and the general quality of the seeing. I suppose that Global Warming has its part to play, but this has been going on for years and not just the last two. Interesting but worrying.’ Like the Director, Mike is located on the wrong side of the Pennines (at least from a meteorological point of view – no offence to Yorkshire folk!), where the usual prevailing westerly air flow is disturbed by the intervening hills. But, even allowing for that, nights of good seeing have become a precious few. Here is a selection from the images received, along with Dale’s sketch. As usual, space does not permit us to reproduce as many as we would wish. 5 ERATOSTHENES, drawn by Dale Holt, 2015 December 4, 06.30 UT. To the right is an image taken by the Director on the same morning at 07.55 UT, col. 188.0°. Sunset over Theophilus and Cyrillus Clyde Foster Clyde Foster (South Africa) writes: ‘After capturing my Mars images on the morning of 1 December, the waning moon was well positioned, so I swung over for a few captures. Seeing was not particularly good, but the lunar sunset gave a different perspective on some of the craters. I used an IR filter with the ASI224MC for this capture. I imaged the 110km-diameter Theophilus which has impinged on the older 100km-diameter Cyrillus. Under these conditions Theophilus B , which is on the western wall of Theophilus is hidden in the shadow. The impressive terraces on the eastern wall are highlighted, whilst the southern wall detail gives an almost molten appearance. A few small mounds and craterlets in north eastern section of the floor are visible. In Cyrillus the inner mountain range on the eastern side of the crater is nicely highlighted as well as the main floor fracture. The impressive looking wall section between Cyrillus and Cyrillus F at the bottom centre must be reasonably flattish at its summit, as the detail shows also on the eastern side of the ridge.’ 6 The Polar Regions Rik Hill and Lars Lindhart For some reason the southern polar regions of the Moon seem to attract much more attention from observers than those of the north. Rik Hill (USA) writes: ‘I would encourage all lunar imagers to take a couple images of the [northern] polar regions when the libration is favorable. This is another such image. Each time I do this I see new features. Lunar libration allows us to see almost 10% more than half the Moon so what you do is wait until it shows more of your area of interest and image that region on that night. A beautiful video demonstrating libration during a full lunation, plus a good detailed explanation, can be found on the Wikipedia page for "lunar libration". The very large, crater at the top of this image is the 108km Hermite. NASA's Lunar Reconnaissance Orbiter (LRO) found this crater to be the coldest place in the solar system at -413° Fahrenheit (−247° Celsius) even colder than Pluto's surface at -382° Fahrenheit, (-229° Celsius)! Just to the left of Hermite is the clear 60km crater Sylvester and between them and above is the extremely foreshortened 32km crater Lovelace. To the lower right of Hermite is the large 57km crater Byrd with the clear, younger 42km crater Gioja on Byrd's southern wall. Above Byrd is a shadow-filled ring that is the 77km crater, Peary. On the far edge of this crater, marked by the arrow, is the lunar north pole, one of the holy grails of libration imaging. 7 Below Gioja are the twin (over-under) craters Main (48km) and below it is Challis (58km). Below them is the deep (2400m) 58km Scoresby. South of Scoresby is the large "walled plain" Meton. It is not simply called a "crater" because it's actually the merging of 4 or 5 craters that were flooded some 4 billion years ago. Barrow is the 95km diameter flooded crater to the left of Meton. Further left is the large, 124km Goldschmidt and finally the younger 53km crater Anaxagoras.’ Meanwhile, Lars Lindhart (Denmark) has submitted a fine panorama of the southern polar regions, and we hope that he will continue to send in his work. 8 Leo Aerts (Belgium) is another European observer who has just started to submit his work to the Section, although he is extremely well known as a fine planetary imager. Again, we hope that Leo will continue to send in his superb lunar images, a couple of examples of which are given below.