Charles Messier is was famous in his day for being the discoverer of comets. Now, he is remembered for his catalogue of nebulae, galaxies and clusters that he created to help comet hunters from being mislead by their appearance.
Among amateur astronomers, this has created the "sport" of the Messier Marathon, an attempt to see the hundred or so objects in a single observing session.
American planetary astronomer Charles Wood, has created a list of sorts for lunar observers. One Hundred features of the Moon, numbered in order of difficulty. Here is my potshot at them!
Yep, the VERY first feature is the Moon itself. Hard to miss, except maybe in the daytime - which is not as daft as it sounds. Observing the moon in the early morning is a good time to see features with a gentler contrast than at night. The only real disadvantage with observing the moon in the daytime is that the atmosphere is heated up and quite disturbed. With winter coming on one of things I want to try is to wait for especially cold clear days and see if atmospheric turbulence is as bad.
One of the most captivating sights is a clear evening with a new, slender crescent moon that has it's unlit side visible as a ghostly counterpart. The normally dark side of the moon is being illuminated by light shining off the earth - hence the name earthshine.
The bright parts of the moon that we can see are generally mountainous uplands. The dark areas are the smooth(ish) surfaces of vast basins of land that are the lunar maria or seas (called this because originally it was thought that was what they were!).
The maria are thought to be the result of large impacts on the moon's surface which caused an upwelling of molten magma, which filled up the impact basin. Maria are composed of a type of basalt rock, rich in iron and titanium. The reflective uplands are composed of rocks similar to granite, but with more feldspar in them.
5 Copernicus - Archetypal large complex crater
6 Tycho - Large rayed crater with impact melts
7 Altai Scarp - Nectaris basin rim
9 Clavius - Lacks basin features in spite of its size
11 Aristarchus - Very bright crater with dark bands on its walls
12 Proclus - Oblique-impact rays
13 Gassendi - Floor-fractured crater
14 Sinus Iridum - Very large crater with missing rim
15 Straight Wall - Best example of a lunar fault
16 Petavius - Crater with domed & fractured floor
17 Schröter's Valley - Giant sinuous rille
18 Mare Serenitatis dark edges - Distinct mare areas with different compositions
19 Alpine Valley - Lunar graben
21 Fracastorius - Crater with subsided & fractured floor
22 Aristarchus Plateau - Mysterious uplifted region mantled with pyroclastics
23 Pico - Isolated Imbrium basin-ring fragment
24 Hyginus Rille - Rille containing rimless collapse pits
25 Messier & Messier A - Oblique ricochet-impact pair
26 Mare Frigoris - Arcuate mare of uncertain origin
28 Hipparchus - First drawing of a single crater
29 Aridaeus Rille - Long linear graben
30 Schiller - Possible oblique impact
31 Taruntius - Young floor-fractured crater
32 Arago Alpha & Beta - Volcanic domes
33 Serpentine Ridge - Basin inner-ring segment
34 Lacus Mortis - Strange crater with rille & ridge
35 Triesnecker Rilles - Rille family
36 Grimaldi basin - A small two-ring basin
37 Bailly - Barely discernible basin
38 Sabine & Ritter - Possible twin impacts
39 Schickard - Crater floor with Orientale basin ejecta stripe
40 Janssen Rille - Rare example of a highland rille
41 Bessel ray - Ray of uncertain origin near Bessel
42 Marius Hills - Complex of volcanic domes & hills
43 Wargentin - A crater filled to the rim with lava or ejecta
44 Mersenius - Domed floor cut by secondary craters
45 Maurolycus - Region of saturation cratering
46 Regiomontanus central peak - Possible volcanic peak
47 Alphonsus dark spots - Dark-halo eruptions on crater floor
48 Cauchy region - Fault rilles & domes
49 Gruithuisen Delta & Gamma - Volcanic domes formed with viscous lavas
50 Cayley Plains - Light smooth plains of uncertain origin
51 Davy crater chain - Result of comet-fragment impacts
52 Crüger - Possible volcanic caldera
53 Lamont - Possible buried basin
54 Hippalus Rilles - Rilles concentric to Humorum basin
55 Baco - Unusually smooth crater floor & surrounding plains
56 Australe basin - A partially flooded ancient basin
57 Reiner Gamma - Conspicuous swirl & magnetic anomaly
59 Schiller-Zucchius basin - Badly degraded overlooked basin
60 Kies Pi - Volcanic dome
61 Mösting - A Simple crater close to center of lunar near side
62 Rümker - Large volcanic dome
63 Imbrium sculpture - Basin ejecta near & overlying Boscovich & Julius Caesar
64 Descartes - Apollo 16 landing site; putative region of highland volcanism
65 Hortensius domes - Dome field north of Hortensius
66 Hadley Rille - Lava channel near Apollo 15 landing site
67 Fra Mauro formation - Apollo 14 landing site on Imbrium ejecta
68 Flamsteed P - Proposed young volcanic crater & Surveyor 1 landing site
69 Copernicus secondary craters - Rays and craterlets near Pytheas
70 Humboldtianum basin - Multi-ring impact basin
71 Sulpicius Gallus dark mantle - Ash eruptions northwest of crater
72 Atlas dark-halo craters - Explosive volcanic pits on the floor of Atlas
73 Smythii basin - Difficult-to-observe basin scarp & mare
74 Copernicus H - Dark-halo impact crater
75 Ptolemaeus B - Saucerlike depression on the floor of Ptolemaeus
76 W. Bond - Large crater degraded by Imbrium ejecta
77 Sirsalis Rille - Procellarum basin radial rilles
78 Lambert R - A buried ghost crater
79 Sinus Aestuum - Eastern dark-mantle volcanic deposit
80 Orientale basin - Youngest large impact basin
81 Hesiodus A - Concentric crater
Well I guess I can say that I've seen it. A small, bright speck on Serenitatus. Of course in the 4" it looks a lot like 100s of other small speck-like craters. So the next trick will be to try and observe it under oblique lighting conditions.
Two views of Plato, drawn about a couple of days apart. The first drawing shows Plato as essentially flat and featureless. Redshift gives the altitude of the sun from Plato as 16º. The second drawing was made a couple of days later and the sun is only about 2º above the horizon and Plato being on the terminator. Seeing was very good on the 4th (1 on the Antoniadii scale.) with occasional moments of shimmering. I was able to reach 338x and still have good sharp definition, but for the drawing I stayed at 120x. The alt-az mounting is a bit rubbery at the highest powers! :-)
The craterlett itself was visible in steady moments, and easily disappeared when the seeing degraded. It appeared mostly as a small bright spot, and in still moments it was quite plain that it was not a dimensionless point but a minute extended area of some kind. To the south-west there appeared to be another small bright spot, but it was less persistent than the first and I was unable to say for sure if it was really there. Rukl shows there is another craterlett there, but adding it in as a "definite", when it was observed as a "maybe" seemed a bit naughty!
The area around Plato is worth a mention. At the time of the first drawing, it seemed as though Plato was surrounded by a "splash" - an area of lighter colour that the maria. However by the time of the second drawing, the sun angle was low enough to throw this into relief and it stood out as a rough and crumpled mountainous region.
Just for fun I measured the length of the shadow from the peak on the rim of Plato and get a (very rough!) height of 1.4km.
|A new picture of Plato. Rather
than scan in a pen drawing (which ended up looking too lumpy) I made this
image straight from the telescope sketch of the crater's albedo. Plato's
floor was uniformly grey but a dark shadow from the eastern wall was
visible and quite striking given that the Moon was nearly full. The
explanation for this is that the sun, although high, was still only 34º
or so above the horizon and was causing a shadow to be cast.
The wedge-shaped feature on the west wall did not have it's usual black outline separating it from the crater wall proper. I have always visualised this feature as a wedge-shaped island of land that has separated somehow from Plato's wall, so I would have expected to see darkness between the "island" and the wall. This was not apparent. I think that maybe the Island is a landslide that has broken from the crater wall and settled.
84 Pitatus - Crater with concentric rilles
85 Langrenus rays - Aged ray system
86 Prinz Rilles - Rille system near the crater Prinz
87 Humboldt - Crater with central peaks and dark spots
88 Peary - Difficult-to-observe polar crater
89 Valentine Dome - Volcanic dome
90 Armstrong Aldrin and Collins - Small craters near the Apollo 11 landing site
91 De Gasparis Rilles - Area with many rilles
92 Gylden Valley - Part of the Imbrium radial sculpture
93 Dionysius rays - Unusual and rare dark rays
94 Drygalski - Large south-pole region crater
95 Procellarum basin - The Moon's biggest basin?
96 Leibnitz Mountains - Rim of South Pole-Aitken basin
97 Inghirami Valley - Orientale basin ejecta
98 Imbrium lava flows - Mare lava-flow boundaries
99 Ina - D-shaped young volcanic caldera
100 Mare Marginis swirls - Possible magnetic field deposits