clair-obscur (/clair-obscur) # Edit ! 7 (/clair-obscur#discussion) " 171 (/page/history/clair-obscur) … (/page/menu/clair-obscur) Clair-Obscur Effects on the moon's surface (Also spelled clair-obscure and clare-obscure) (glossary entry) Table of Contents Clair-Obscur Effects on the moon's surface Description Additional Information List of Clair-Obscur Effects and Informal Optical Feature Names Quadrant 1 Quadrant 2 Quadrant 3 Quadrant 4 Other Informal Optical Feature Names New terminator-page? LPOD Articles APOD articles Bibliography Description French for "light" (clair) and “shadow” (obscur): the term is used here to mean any effect on the Moon's surface created by the interplay of light and shadow. See also: Pareidolia and Trompe-l'oeil Additional Information The term clair-obscur was reportedly introduced by seventeenth century French painter and art-critic Roger de Piles in a discussion of effects that could be created with color and drawing. In connection with paintings, the equivalent Italian expression chiaroscuro is now more often used to express the same idea. Most clair-obscur effects on the Moon are short-lived, but they are not one-time or rare events. Because lunar lighting patterns repeat in a cycle of approximately 29.5 days, each effect can be observed from somewhere on Earth once every month. The 0.5 day part of http://the-moon.wikispaces.com/clair-obscur#Clair-Obscur%…Effects%20and%20Informal%20Optical%20Feature%20Names 07/07/2018, 08H00 Page 1 of 16 the lunar cycle gives many observers the impression that many of these effects are rarer than they actually are. Because of the 0.5 day part, a particular effect can typically be observed from a given location at most once every other month (because in the alternate months, for that observer, the event occurs during daylight hours or when the Moon is below the horizon). As indicated in the following list, many clair-obscur effects on the Moon have been described, and some have been given informal names. Some of these names are relatively well known; but most are pet names, often recognized by only a handful of observers. Most apply to a specific surface feature, or group of surface features; but unlike other informal and unofficial feature names, they are applied to those features only when they are seen with a particular lighting. Since the IAU does not assign names to lighting patterns, none of these are "official" lunar names, nor do they even have the possibility of becoming official. The names should be used with caution because, as with all other informal and unofficial names, the same name may have been used by another observer to mean something completely different; and, conversely, the same effect may be differently named by different observers. List of Clair-Obscur Effects and Informal Optical Feature Names Four quadrants list of well known and rather unknown clair-obscur effects, related to the lunar morning and evening terminator. Quadrant 1 (the northeastern part of the moon's near side) The Zeno steps near or at crater Zeno (an evening-terminator effect which was photographed by the dedicated lunar observer Stefan Lammel). The Lunar V north-northeast of Ukert M (this is a rather large clair-obscur effect, observable through small telescopes, during local sunrise). This effect is observable at about the same moment of the Lunar X 's appearance. O'Neill's Bridge between Promontorium Lavinium and Promontorium Olivium. See LPOD; jan 22th, 2009: Fallen Bridge. Barrow's shaft of light (on the floor and western wall of Barrow). A morning terminator effect. See LPOD; may 13th, 2008. Alexander's beaded rim. The "crackled" illumination of the western "half" of the degraded crater Alexander during sunrise (a curious "Jeweled Handle" appearance, a bit like the larger "handle" at the Montes Jura/ Sinus Iridum). Observed by Danny Caes. See photograph by Stefan Lammel . The Hayn-Belkovich shadow, when it's two-days-before-Full-Moon. Hayn and Belkovich are two craters near the moon's northeastern limb, and curiously enough, there's a black shadow in (or near?) these craters when it's about two days before Full Moon, which is too soon to be part of the eastern limb's evening terminator! (observed by Danny Caes during the night of march the 3th, 1996)(there was Full Moon at march the 5th). The same http://the-moon.wikispaces.com/clair-obscur#Clair-Obscur%…Effects%20and%20Informal%20Optical%20Feature%20Names 07/07/2018, 08H00 Page 2 of 16 phenomenon observed on january the 3th, 2015 (Full Moon on the 5th). Posidonius' illuminated rim during local sunset (evening terminator at about 30 degrees east over Posidonius). Observed by Danny Caes on 19-9-'08 at 23.00 U.T., Orion- SkyQuest Dobsonian. The "L"-shaped mountain at 43° north/ 11° east (in the northern part of the Montes Caucasus) is an interesting telescopic target during Full Moon, when the western slope of its north-south oriented part, and the southern slope of its east-west oriented part, look very much like an illuminated "L" or "sunlit corner". It is unofficially called Mons Elbruz by Danny Caes (note: the Terrestrial Mount Elbruz is also located in the Caucasus range). The Caucasus X. An X-shaped appearance in that part of Montes Caucasus west- northwest of Eudoxus, observable during the local morning illumination. Discovered by Luka Giacomelli, see his photography of Eudoxus region (The Caucasus X is marked with red rounded rectangle). Cauchy's interrupted western shadow, when the morning-terminator runs at about two degrees west of Cauchy. The northern and southern parts of Cauchy's western shadow are untouched, the central part of it seems absent. A curious effect! Paolo Lazzarotti's LPOD of Cauchy and surroundings shows Cauchy's "interrupted" shadow very well! (see also at Wilkins's Lenham in Quadrant 3). Aratus CA's illuminated eastern inner slope. Although Aratus CA is basically a rimless depression, it can be seen as a bright dot when the sun is very low to the west. It would appear that the Sun's setting rays are able to shine down Vallis Christel and strike the east wall of the pit between Vallis Krishna and Rima Sung-Mei. Research: Jim Mosher. Quadrant 2 (the northwestern part of the moon's near side) Gruithuisen's so-called lunar city, north-northwest of crater Schröter (disappears during high-sun). Cassini's Moon Maiden at Promontorium Heraclides (a morning-terminator effect). See Bibliography. The Golden Handle effect or Jewelled Handle at Montes Jura and Sinus Iridum (a classic morning-terminator effect which is observable through small binoculars!). This effect appears exactly 24 hours after the morning terminator's location at Copernicus, which, for us, is a very good indicator! See also LPOD Half A Circle and LPOD 24 Hours. Buzz Saw (the opposite of the Jewelled Handle effect), see: https://www.cloudynights.com/topic/551293-next-lunar-buzz-saw-early-monday-morning- sept-26/ Two bright stars at Mons Pico and Pico Beta, when the morning terminator runs east of these two peaks. A well-known phenomenon, observable through small telescopes and binoculars. Babbage A's illuminated rim when the morning-terminator is at 55° West. The floor of Babbage itself is still in darkness, while Babbage A's rim is already in sunlight. Observed by Danny Caes. Pythagoras's illuminated central peak, when the floor of Pythagoras is still in darkness http://the-moon.wikispaces.com/clair-obscur#Clair-Obscur%…Effects%20and%20Informal%20Optical%20Feature%20Names 07/07/2018, 08H00 Page 3 of 16 during the local sunrise (looks quite "pronounced" and "steep"). See LPOD Textures. Crater Plato's hook. Ashen Light on Plato's floor (or is it some sort of TLP?). See Phil Morgan's exquisite drawing in LPOD Milk of Plato. Copeland's star tip mountain (Mons Herodotus)(a morning-terminator effect). See LPOD dec 14, 2008. Crater Carlini's double shadow during local sunrise. See Bibliography. Lambert Gamma (incorrectly labeled Mons Undest -Mons Undset- on LTO-40B4 ). Before local sunrise it (Lambert Gamma) looks like a very bright "star" on the shadowed part of Mare Imbrium). The two stars at Mons Ampère and Mons Huygens (a morning-terminator effect which was discovered (or re-discovered?) by Danny Caes. See also LPOD A New Look Crater Dechen's flat dish appearance (a morning-terminator effect). Crater Lavoisier A's dish-shaped appearance when the morning terminator runs at about 75 degrees West. Crater Wallace's three shadow-spires (a morning-terminator effect). See also AS17-153- 23591 , which is the last one of a small series showing orbital views of Wallace during local sunrise. Research Danny Caes. Wallace's illuminated ring effect during local sunrise. See LPOD may 6th, 2009. Distinct short illuminated streak at 17°45' North/ 6°10' West (a morning-terminator effect). Crater T. Mayer A's bright illuminated ring appearance (a morning-terminator effect). Crater Aristillus B's rim which is "cut in half" when the shadow of one of Montes Spitzbergen's peaks is projected upon it (an evening-terminator effect). See Bibliography. Maupertuis' Moonmaiden at the eastern part of Maupertuis, during local sunset (evening-terminator). Should be observed through a prism-less telescope, on Earth's northern hemisphere. In other words; moon's north at the bottom, south up. The solemn looking face at 16° North/ 6° West (southeast of Mons Wolf). This is a rather difficult-to-recognize clair/obscur effect, because of the face itself (which looks northeast- ward in a rather "solemn" manner). A morning terminator effect. The location of the face is also visible on Apollo 17's Nikon photograph AS17-160-23946 , below centre.