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The Lunar 100

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The Moon is extremely rich and varied in surface detail. However, when Charles A. Wood introduced amateur astronomers to his list of 100 object or features on the Moon, he wrote (Wood 2004a, 2012a):

... many backyard astronomers never go beyond the astro-tourist stage to acquire the knowledge and understanding necessary to really appreciate what they're looking at, and how magnificent and amazing it truly is. Perhaps this is because after they identify a few of the Moon's most conspicuous features, many amateurs don't know where to look next.

His list of 100 features on or of the Moon intends to offer a good cross section, similar to the Messier catalogue for deep-sky objects. The list begins with easy targets and has some extremely difficult ones toward the end. The list itself can be found online in the 2012 article. The Wikipedia page "Lunar 100" (Wikipedia 2021a) is slightly better. Wood also made much more detailed notes available to the Stargazers' Lounge (Hardwick 2013a). The notes betray a bias toward visual observing with a large telescope, but this need not stop imagers to capture virtually all 100 entries. There is also a bias toward observing during the first half of the lunation, between New and Full Moon. This will suit most observers, who prefer the first half of the night to the second.

The placeholder image is taken from van Gogh (1889a). To do the objects justice, consult Wood's notes (Hardwick 2013a) and also use the Atlas virtuel de la Lune (Chevalley and Legrand 2012a). Without these, it can be unclear which is the Lunar 100 object.

Lunar 1 to 12

Lunar 1: Moon Lunar 2: Earth shine Lunar 3: mare/highland dichotomy Lunar 4: Montes Appenninus

Lunar 5: Copernicus Lunar 6: Tycho Lunar 7: Rupes Altai Lunar 8: Theophilus, Cyrillus, Catharina

Lunar 9: Clavius Lunar 10: Mare Crisium Lunar 11: Aristarchus Lunar 12: Proclus

The first three entries are unconventional. They are named "Moon", "Earthshine" and "mare/highland dichotomy"; and Wood's notes provide no information. Objects within the first dozen include a few very prominent craters, a mountain range (montes), a smallish mare, and a scarp or dorsa.

The maria originated in very large impacts that smashed through the lunar crust so that lava from the interior flooded the crater. The result is a darker and much more even surface. These large impacts must have been relatively recent, because the plethora of craters of the highland regions have by and large not destroyed the mare floors. The opposite is true, the maria impacts destroyed large regions of crater-strewn highlands.

Lunar craters are very varied. They are not volcanoes, but result from the impact of meteorites. The largest are 250 km in diameter. Old craters have newer craters within them or superimposed on their wall, large craters have central mountains and terraced rims; some of them have bright "rays" of ejecta.

The rims of maria create mountain ranges (montes). There are steps of perhaps 100 m height in maria. These are called dorsa or rupes and can be seen when close to the terminator (the boundary between light and shadow). In fact, all features are better observed not far from the terminator, as it is mostly the play of light and shadow that allows us to see these features.

Rupes Altai is a little different. It is a scarp in a highland region and rather higher than your average dorsa. It is concentric to Mare Nectaris, so will be related to that major impact.

Lunar 13 to 24

Lunar 13: Gassendi Lunar 14: Sinus Iridum Lunar 15: Rupes Recta Lunar 16: Petavius

Lunar 17: Vallis Schröteri Lunar 18: Mare Serenitatis dark edges Lunar 19: Vallis Alpes Lunar 20: Posidonius

Lunar 21: Fracastorius Lunar 22: Aristarchus Plateau Lunar 23: Mons Pico Lunar 24: Rima Hyginus

This dozen objects include further prominent craters, a large bay (sinus), a remarkably straight dorsa, two quite different valleys (valles), a colour/brightness contrast within a mare floor, an isolated mountain (mons) within a mare, and our first rille (rima).

Lunar 25 to 36

Lunar 25: Messier and Messier A Lunar 26: Mare Frigoris Lunar 27: Archimedes Lunar 28: Hipparchus

Lunar 29: Rima Ariadaeus Lunar 30: Schiller Lunar 31: Taruntius Lunar 32: Arago α and β

Lunar 33: Dorsa Smirnov Lunar 34: Lacus Mortis Lunar 35: Rimae Triesnecker Lunar 36: Grimaldi

New types of features here are the peculiar rays of Messier and Messier A, the oddly shaped Mare Frigoris, some more rilles, domes near the crater Arago, a lake (lacus), and an archetypical dorsa.

Lunar 37 to 48

Lunar 37: Bailly Lunar 38: Sabine and Ritter Lunar 39: Schickard Lunar 40: Rimae Janssen

Lunar 41: Bessel ray Lunar 42: Marius Hills Lunar 43: Wargentin Lunar 44: Mersenius

Lunar 45: Maurolycus Lunar 46: Regiomontanus central peak Lunar 47: Alphonsus Lunar 48: Cauchy region

Lunar 49 to 60

Lunar 49: Gruithuisen δ and γ Lunar 50: Cayley plains Lunar 51: Catena Davy Lunar 52: Crüger

Lunar 53: Lamont Lunar 54: Rimae Hippalus Lunar 55: Baco Lunar 56: Mare Australe

Lunar 57: Reiner γ Lunar 58: Vallis Reita Lunar 59: Schiller-Zucchius basin Lunar 60: Kies π

Lunar 61 to 72

Lunar 61: Mösting A Lunar 62: Mons Rümker Lunar 63: Imbrium sculpture Lunar 64: Descartes

Lunar 65: Hortensius domes Lunar 66: Rima Hadley Lunar 67: Fra Mauro Lunar 68: Flamsteed P

Lunar 69: Pytheas craterlets Lunar 70: Mare Humboldtianum Lunar 71: Sculpicius Gallus dark mantle Lunar 72: Atlas

Lunar 73 to 84

Lunar 73: Mare Smythii Lunar 74: Copernicus H Lunar 75: Ptolemaeus B Lunar 76: W. Bond

Lunar 77: Rimae Sirsalis Lunar 78: Lambert R Lunar 79: Sinus Aestuum Lunar 80: Mare Orientale

Lunar 81: Hesiodus A Lunar 82: Linné Lunar 83: Plato craterlets Lunar 84: Pitatus

Lunar 85 to 100

Lunar 85: Langrenus rays Lunar 86: Rimae Prinz Lunar 87: Humboldt Lunar 88: Peary

Lunar 89: Valentine dome Lunar 90: Armstrong, Aldrin, Collins Lunar 91: Rimae de Gasparis Lunar 92: Vallis Gyldén

Lunar 93: Dionysius rays Lunar 94: Drygalski Lunar 95: Oceanus Procellarum Lunar 96: Leibnitz mountains

Lunar 97: Vallis Inghirami Lunar 98: Imbrium lava flows Lunar 99: Ina depression Lunar 100: Mare Marginis swirls