
Many Lunar 100 selections are plainly visible in this image of the full Moon, while others require a more detailed view, different illumination, or favorable libration. North is up.
S&T: Gary Seronik
Just about every telescope user is familiar with French comet hunter Charles Messier's catalog of fuzzy objects. Messier's 18th-century listing of 109 galaxies, clusters, and nebulae contains some of the largest, brightest, and most visually interesting deep-sky treasures visible from the Northern Hemisphere. Little wonder that observing all the M objects is regarded as a virtual rite of passage for amateur astronomers.
But the night sky offers an object that is larger, brighter, and more visually captivating than anything on Messier's list: the Moon. Yet 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.
The Lunar 100 list, featured in the April 2004 issue of Sky & Telescope is an attempt to provide Moon lovers with something akin to what deep-sky observers enjoy with the Messier catalog: a selection of telescopic sights to ignite interest and enhance understanding. Presented here is a selection of the Moon's 100 most interesting regions, craters, basins, mountains, rilles, and domes. I challenge observers to find and observe them all and, more important, to consider what each feature tells us about lunar and Earth history.
Anatomy of the Lunar 100
Objects in the Lunar 100 are arranged from the easiest to view to the most difficult. This is more systematic than the haphazard approach that produced the Messier list. Indeed, just by knowing a feature's Lunar 100 number, you have some idea of how easy or challenging it will be to see. For example, the Moon itself is L1, while L2 is earthshine and L3 is the light/dark dichotomy between lunar highlands and maria ("seas"). I'd be surprised if anyone reading this couldn't tick those off the list right now. Higher-numbered objects are smaller, less conspicuous, or positioned closer to the limb, making them more challenging to locate and view.

Planetary scientist Charles Wood's Lunar 100 is a list of telescopic sights designed to ignite interest in the Moon and enhance understanding of its geology.
Source: Antonín Rükl
The Messier objects are scattered all over the sky, but all are theoretically observable during marathon nights in March and April every year. By contrast, the Lunar 100 are concentrated in just ½°of sky, yet they can't all be seen in a single night, or even in a single month. Some lunar objects can be observed only with grazing solar illumination, while others are albedo features that require full-Moon conditions to be seen. And others are positioned near (or sometimes even over) the limb of the Moon, requiring a very favorable libration to bring them into view. I don't know how quickly all 100 can be observed, but I'm sure that some competitive amateur will complete it faster than I dare guess!
How big a telescope do you need to view the Lunar 100? The smallest features listed are 3 kilometers in diameter and thus nominally visible in 3-inch (75-millimeter) telescopes employing magnifications of about 150× to 200×. And many can be found with smaller scopes at lower power. But a few Lunar 100 objects — such as narrow rilles — are best seen with 6- or 8-inch telescopes used at high power. The goal, however, is not just to find the objects, but to understand what they tell us abut the Moon.
Any selection of lunar features is bound to lead to many difficult judgments, and I'm sure that at least a few of my choices and rankings will generate considerable debate. Some of my choices were obvious, some were not. Some were influenced by my personal sense of what crater appears more dramatic than another, or which rille best demonstrates an aspect of the Moon's evolution. Aesthetics aside, my choices were principally governed by a desire to include features that tell us something important or interesting about the Moon itself.
I invite you to use the Lunar 100 to guide your explorations of the Moon.
The Lunar 100 | ||||||
L | Feature Name | Significance | Lat. (°) | Long. (°) | Diam. (km) | Rükl Chart |
1 | Moon | Large satellite | — | — | 3,476 | — |
2 | Earthshine | Twice reflected sunlight | — | — | — | — |
3 | Mare/highland dichotomy | Two materials with distinct compositions | — | — | — | — |
4 | Apennines | Imbrium basin rim | 18.9N | 3.7W | 70 | 22 |
5 | Copernicus | Archetypal large complex crater | 9.7N | 20.1W | 93 | 31 |
6 | Tycho | Large rayed crater with impact melts | 43.4S | 11.1W | 85 | 64 |
7 | Altai Scarp | Nectaris basin rim | 24.3S | 22.6E | 425 | 57 |
8 | Theophilus, Cyrillus, Catharina | Crater sequence illustrating stages of degradation | 13.2S | 24.0E | — | 46, 57 |
9 | Clavius | Lacks basin features in spite of its size | 58.8S | 14.1W | 225 | 72 |
10 | Mare Crisium | Mare contained in large circular basin | 18.0N | 59.0E | 540 | 26, 27, 37, 38 |
11 | Aristarchus | Very bright crater with dark bands on its walls | 23.7N | 47.4W | 40 | 18 |
12 | Proclus | Oblique-impact rays | 16.1N | 46.8E | 28 | 26 |
13 | Gassendi | Floor-fractured crater | 17.6S | 40.1W | 101 | 52 |
14 | Sinus Iridum | Very large crater with missing rim | 45.0N | 32.0W | 260 | 10 |
15 | Straight Wall | Best example of a lunar fault | 21.8S | 7.8W | 110 | 54 |
16 | Petavius | Crater with domed & fractured floor | 25.1S | 60.4E | 177 | 59 |
17 | Schröter's Valley | Giant sinuous rille | 26.2N | 50.8W | 168 | 18 |
18 | Mare Serenitatis dark edges | Distinct mare areas with different compositions | 17.8N | 23.0E | N/A | 24 |
19 | Alpine Valley | Lunar graben | 49.0N | 3.0E | 165 | 4 |
20 | Posidonius | Floor-fractured crater | 31.8N | 29.9E | 95 | 14 |
The Lunar 100 (continued) | ||||||
L | Feature Name | Significance | Lat. (°) | Long. (°) | Diam. (km) | Rükl Chart |
21 | Fracastorius | Crater with subsided & fractured floor | 21.5S | 33.2E | 124 | 58 |
22 | Aristarchus Plateau | Mysterious uplifted region mantled with pyroclastics | 26.0N | 51.0W | 150 | 18 |
23 | Pico | Isolated Imbrium basin-ring fragment | 45.7N | 8.9W | 25 | 11 |
24 | Hyginus Rille | Rille containing rimless collapse pits | 7.4N | 7.8E | 220 | 34 |
25 | Messier & Messier A | Oblique ricochet-impact pair | 1.9S | 47.6E | 11 | 48 |
26 | Mare Frigoris | Arcuate mare of uncertain origin | 56.0N | 1.4E | 1600 | 2–6 |
27 | Archimedes | Large crater lacking central peak | 29.7N | 4.0W | 83 | 12, 22 |
28 | Hipparchus | First drawing of a single crater | 5.5S | 4.8E | 150 | 44, 45 |
29 | Ariadaeus Rille | Long, linear graben | 6.4N | 14.0E | 250 | 34 |
30 | Schiller | Possible oblique impact | 51.9S | 39.0W | 180 | 71 |
31 | Taruntius | Young floor-fractured crater | 5.6N | 46.5E | 56 | 37 |
32 | Arago Alpha & Beta | Volcanic domes | 6.2N | 21.4E | 26 | 35 |
33 | Serpentine Ridge | Basin inner-ring segment | 27.3N | 25.3E | 155 | 24 |
34 | Lacus Mortis | Strange crater with rille & ridge | 45.0N | 27.2E | 152 | 14 |
35 | Triesnecker Rilles | Rille family | 4.3N | 4.6E | 215 | 33 |
36 | Grimaldi basin | A small two-ring basin | 5.5S | 68.3W | 430 | 39 |
37 | Bailly | Barely discernible basin | 66.5S | 69.1W | 303 | 71 |
38 | Sabine & Ritter | Possible twin impacts | 1.7N | 19.7E | 30 | 35 |
39 | Schickard | Crater floor with Orientale basin ejecta stripe | 44.3S | 55.3W | 227 | 62 |
40 | Janssen Rille | Rare example of a highland rille | 45.4S | 39.3E | 190 | 67, 68 |
The Lunar 100 (continued) | ||||||
L | Feature Name | Significance | Lat. (°) | Long. (°) | Diam. (km) | Rükl Chart |
41 | Bessel ray | Ray of uncertain origin near Bessel | 21.8N | 17.9E | N/A | 24 |
42 | Marius Hills | Complex of volcanic domes & hills | 12.5N | 54.0W | 125 | 28, 29 |
43 | Wargentin | A crater filled to the rim with lava or ejecta | 49.6S | 60.2W | 84 | 70 |
44 | Mersenius | Domed floor cut by secondary craters | 21.5S | 49.2W | 84 | 51 |
45 | Maurolycus | Region of saturation cratering | 42.0S | 14.0E | 114 | 66 |
46 | Regiomontanus central peak | Possible volcanic peak | 28.0S | 0.6W | 124 | 55 |
47 | Alphonsus dark spots | Dark-halo eruptions on crater floor | 13.7S | 3.2W | 119 | 44 |
48 | Cauchy region | Fault, rilles, & domes | 10.5N | 38.0E | 130 | 36 |
49 | Gruithuisen Delta & Gamma | Volcanic domes formed with viscous lavas | 36.3N | 40.0W | 20 | 9 |
50 | Cayley Plains | Light, smooth plains of uncertain origin | 4.0N | 15.1E | 14 | 34 |
51 | Davy crater chain | Result of comet-fragment impacts | 11.1S | 6.6W | 50 | 43 |
52 | Crüger | Possible volcanic caldera | 16.7S | 66.8W | 45 | 50 |
53 | Lamont | Possible buried basin | 4.4N | 23.7E | 106 | 35 |
54 | Hippalus Rilles | Rilles concentric to Humorum basin | 24.5S | 29.0W | 240 | 52, 53 |
55 | Baco | Unusually smooth crater floor & surrounding plains | 51.0S | 19.1E | 69 | 74 |
56 | Australe basin | A partially flooded ancient basin | 49.8S | 84.5E | 880 | 76 |
57 | Reiner Gamma | Conspicuous swirl & magnetic anomaly | 7.7N | 59.2W | 70 | 28 |
58 | Rheita Valley | Basin secondary-crater chain | 42.5S | 51.5E | 445 | 68 |
59 | Schiller-Zucchius basin | Badly degraded overlooked basin | 56.0S | 45.0W | 335 | 70, 71 |
60 | Kies Pi | Volcanic dome | 26.9S | 24.2W | 45 | 53 |
The Lunar 100 (continued) | ||||||
L | Feature Name | Significance | Lat. (°) | Long. (°) | Diam. (km) | Rükl Chart |
61 | Mösting A | Simple crater close to center of lunar near side | 3.2S | 5.2W | 13 | 43 |
62 | Rümker | Large volcanic dome | 40.8N | 58.1W | 70 | 8 |
63 | Imbrium sculpture | Basin ejecta near & overlying Boscovich & Julius Caesar | 11.0N | 12.0E | — | 34 |
64 | Descartes | Apollo 16 landing site; putative region of highland volcanism | 11.7S | 15.7E | 48 | 45 |
65 | Hortensius domes | Dome field north of Hortensius | 7.6N | 27.9W | 10 | 30 |
66 | Hadley Rille | Lava channel near Apollo 15 landing site | 25.0N | 3.0E | — | 22 |
67 | Fra Mauro formation | Apollo 14 landing site on Imbrium ejecta | 3.6S | 17.5W | — | 42 |
68 | Flamsteed P | Proposed young volcanic crater & Surveyor 1 landing site | 3.0S | 44.0W | 112 | 40 |
69 | Copernicus secondary craters | Rays & craterlets near Pytheas | 19.6N | 19.1W | 4 | 20 |
70 | Humboldtianum basin | Multi-ring impact basin | 57.0N | 80.0E | 650 | 7 |
71 | Sulpicius Gallus dark mantle | Ash eruptions northwest of crater | 19.6N | 11.6E | 12 | 23 |
72 | Atlas dark-halo craters | Explosive volcanic pits on the floor of Atlas | 46.7N | 44.4E | 87 | 15 |
73 | Smythii basin | Difficult-to-observe basin scarp & mare | 2.0S | 87.0E | 740 | 38, 49 |
74 | Copernicus H | Dark-halo impact crater | 6.9N | 18.3W | 5 | 31 |
75 | Ptolemaeus B | Saucerlike depression on the floor of Ptolemaeus | 8.0S | 0.8W | 16 | 44 |
76 | W. Bond | Large crater degraded by Imbrium ejecta | 65.3N | 3.7E | 158 | 4 |
77 | Sirsalis Rille | Procellarum basin radial rilles | 15.7S | 61.7W | 425 | 39, 50 |
78 | Lambert R | A buried "ghost" crater | 23.8N | 20.6W | 54 | 20 |
79 | Sinus Aestuum | Eastern dark-mantle volcanic deposit | 12.0N | 3.5W | 90 | 33 |
80 | Orientale basin | Youngest large impact basin | 19.0S | 95.0W | 930 | 50 |
The Lunar 100 (continued) | ||||||
L | Feature Name | Significance | Lat. (°) | Long. (°) | Diam. (km) | Rükl Chart |
81 | Hesiodus A | Concentric crater | 30.1S | 17.0W | 15 | 54 |
82 | Linné | Small crater once thought to have disappeared | 27.7N | 11.8E | 2.4 | 23 |
83 | Plato craterlets | Crater pits at limits of detection | 51.6N | 9.4W | 101 | 3, 4 |
84 | Pitatus | Crater with concentric rilles | 29.8S | 13.5W | 97 | 54 |
85 | Langrenus rays | Aged ray system | 8.9S | 60.9E | 132 | 49 |
86 | Prinz Rilles | Rille system near the crater Prinz | 27.0N | 43.0W | 46 | 19 |
87 | Humboldt | Crater with central peaks & dark spots | 27.0S | 80.9E | 207 | 60 |
88 | Peary | Difficult-to-observe polar crater | 88.6N | 33.0E | 74 | 4, II |
89 | Valentine Dome | Volcanic dome | 30.5N | 10.1E | 30 | 13 |
90 | Armstrong, Aldrin & Collins | Small craters near the Apollo 11 landing site | 1.3N | 23.7E | 3 | 35 |
91 | De Gasparis Rilles | Area with many rilles | 25.9S | 50.7W | 30 | 51 |
92 | Gylden Valley | Part of the Imbrium radial sculpture | 5.1S | 0.7E | 47 | 44 |
93 | Dionysius rays | Unusual & rare dark rays | 2.8N | 17.3E | 18 | 35 |
94 | Drygalski | Large south-pole region crater | 79.3S | 84.9W | 162 | 72, VI |
95 | Procellarum basin | The Moon's biggest basin? | 23.0N | 15.0W | 3200 | — |
96 | Leibnitz Mountains | Rim of South Pole-Aitken basin | 85.0S | 30.0E | — | 73, V |
97 | Inghirami Valley | Orientale basin ejecta | 44.0S | 73.0W | 140 | 61 |
98 | Imbrium lava flows | Mare lava-flow boundaries | 32.8N | 22.0W | — | 10 |
99 | Ina | D-shaped young volcanic caldera | 18.6N | 5.3E | 3 | 22 |
100 | Mare Marginis swirls | Possible magnetic field deposits | 18.5N | 88.0E | — | 27, III |
Chart numbers refer to Antonín Rükl's Atlas of the Moon. |
For the convenience of observers, the Lunar 100 is also available on Sky & Telescope's 9-by-12-inch laminated Lunar 100 Card ($6.95), featuring a high-quality Moon map by Antonin Rukl on the front. The reverse side shows the locations and sizes of 100 features, together with brief descriptions of each.
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