images from various observers, collected by Jean-Louis Leroy, France
The recent LPOD of February 6 shows two photographs of Werner, a crater which displays an interesting bright spot on its north wall. One can find in the Web several reports of observers who recall that it may be the brightest spot on the Moon. At least, this is true for high solar elevations: when the Sun lowers, the picture becomes puzzling, with fast unexpected changes. At the beginning of the 20th century, visual observers attempted to understand the reason behind these variations but they did not really succeed. A good example is the series of drawings by Gerard Fournier published in l’Astronomie (April 1954, p 155-159). The high resolution images of the Moon which are currently obtained now allow a deeper investigation. I assembled a collection of Werner pictures (found on the Web), obtained for eight different illuminations, which explains the observed changes. At last half a dozen small craters have produced high albedo ejecta which make up the bright spot as long as the Sun is high. But, for a lower Sun, the small craters become dark points, thus changing drastically the picture. We are just at the threshold of resolution of the craters and it remains difficult to follow the exact topography of the region: e.g. the small craters look different for the waxing phases (top) and for the waning phases (bottom). Therefore, images with a still higher resolution, which probably require apertures larger than 20 cm, would be of great value to understand completely this region.
The origin of the photographs found in the Web is as follows. From left to right, top: Bob Pilz, LPOD 6 February 2007; Idem; Damian Peach; Clementine 3.74-27.27
Bottom: Obs. Pleine Lune; Ed. Roach; J. Mc Gaba; Clementine 2.66-27.39. I thank these imagers for the use of their images!
Rükl plate 55
Yesterday's LPOD: A Dike, a Rille & a Dome
Tomorrow's LPOD: Wikimoon