Many of these are optical illusions, tricks of lighting as the angle of the rising Sun slowly changes, casting shadows across the lunar landscape. Veteran lunar observer Charles Wood made a call in Sky and Telescope magazine to fill out the visual lunar alphabet in a similar fashion akin to Galaxy Zoo… hey, who wouldn’t love to spell out their name in craters? Maybe some of the recently mapped worlds such as Mercury, Pluto or Ceres could come to the rescue, filling in the final letters? Of course, circular craters provide a wealth of candidates for the ‘Lunar O,’ and straight line features such as the Rupes Recta lunar straight wall feature in the Mare Nubium could easily pass for the ‘Lunar I’. The ‘Lunar Q’ feature… Image credit: NASA/LROC. You can see a partial listing of lunar letters in the WikiMoon article here. Other lunar letters of note include the Lunar S in Sinus Asperitatis (visible at 47% illumination just before First Quarter), the Lunar W located near Mons Rümker on the lunar limb in the Oceanus Procellarum, and our favorite of the lesser known lunar letters, the Lunar Q of crater Kies in the Mare Nubium reaching favorable illumination 10 days after New. Sweeping northward, the Lunar V feature in the Mare Vaporum is also sometimes prominent around the same time as the Lunar X, and it’s possible to nab both in the same image.ĭoubloons! Look for the lunar ‘S’ on the 19th September 2015 /rTnApfKQXg Sometimes, the Curtiss Cross feature is referred to as a lesser known Lunar X the confluence of two or more crater rims on the battered surface of the Moon is far from uncommon. All hail the ‘Lunar X’… image credit: Dave Dickinson. Remember, the span of sunrise to sunset lasts two weeks on the Moon, and looking Earthward, you’d see the Earth in an opposite phase. The Lunar X can stand out in dramatic contrast against the darkness just beyond the lunar terminator, if you can catch it just as the first rays of sunlight hits the top of the ridge. The Lunar X becomes visible as the waxing gibbous Moon reaches seven days illumination, about 6 to 10 hours (depending on the incident sun angle) after First Quarter phase, and 6 to 10 hours before Last Quarter. This is the confluence of the rims of the craters La Caille, Blanchinus and Purbach located in the lunar highlands. One of the most famous of the lunar letters is the Lunar X, also referred to as the Werner X or Purbach Cross. A glimpse of the far side had to wait until the Soviet Luna 3 spacecraft flew past the Moon on October 7 th, 1959 and returned the first blurry images. The subtle rocking motions known as libration and nutation allow us to peer over the edge just a bit, allowing us to see 59% of the Moon’s total surface. Revera.Ī cosmic Rorschach test, the Moon is tidally locked in the Earth’s embrace, keeping its far side forever hidden from our terrestrial vantage point. Image credit: Wikimedia Commons/ Peter Freiman(Cmglee). The annotated features on the lunar nearside.
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