When the libration is right you get a rare view of a huge crater that is normally out of sight. Here you can see it as a large oval near the limb with black basaltic flooded areas on its floor and a sparkling white offset central peak. This is the great crater Humbolt (213km dia.) named after the explorer, naturalist and geographer that was the mentor of Louis Agassiz. This presentation gives us a nice demonstration of just how shallow these grand depressions are. It has huge cliffs on the far side and a floor covered with rimae just barely seen from earth view here. These were likely caused from settling of the flooded floor as it cooled. Adjacent to the near side of Humbolt is the ghostly outline the crater Phillips (128km). Just beyond Phillips is a small bright floored crater Phillips A (13km).
In the upper left corner of this image is the fabulous crater Petavius with the famous large rima running out to the lower left from the bright splatter of the central peaks. Then directly between Petavius and Humbolt is the outline of the crater Legendre (82km).
I don't usually get to see sunset terminators because of the mountains and trees to my east so this night was a treat because the moon was at such a high declination that it was overhead. A number of my favorites were in one field of view here. The large crater at the top is Aristoteles (90 km dia.) with Mitchell (31 km) taking a bite out of its southeast (lower right) wall. Due south of this pair is Eudoxus (70 km) and east of that, deep in shadow, is Burg (41 km) in the center of the hexagonal Lacus Mortis. All three of these large craters are recent by lunar standards. The latter two are Copernican age of 1.1 billion years or less while Aristoteles is a older, Eratosthean age between 1.1-3.2 billion years. But if you want something really old, Lacus Mortis, is Pre-Imbrian age may be as much as 4.5 billion years old, that's 18 rotations of our galaxy ago!!
The area around Tycho is so busy that you have to study it in pieces. Here we start with Tycho (88km dia.) on left of center fand look to the east (right). One of the first things we run into is below and east of Tycho and the largest named crater in this image, Maginus (168km) an oft overlooked crater lying between the spectacular Tycho and magnificent Clavius (just off the southern edge of this image). Between Tycho and Maginus is the crater Street ( 60km). Then below and to the right of Maginus is a sideways Mickey Mouse formed by three craters. The larger crater in this trio is Deluc (49km). From Tycho going east we see Pictet (65km) almost adjacent and further is Saussure (56km) with and interesting flat bottom. Above this last crater is another large one, Orontius (126km) with a triplet of craters just east of it in order, Huggins (66km), Nasireddin (54km) and above it Miller (77km). Notice the central peak in this last crater and the material flooded into the southern floor up to that peak. Nasireddin has some nice terraced walls to enjoy and a curious merge of three craters just outside the southeastern wall. But by far the most interesting terraced walls are in the crater due north of Tycho near the top edge of this image. This is Ball (43km) on the southern edge of Deslandres just outside this north edge of this image.
Notice over this whole image there is a splattering of secondary craters from 5km diameter on down beyond the resolution limit of this image (about 1.5km). Many of these were created in the Tycho impact around 100 million years ago while most the rest of the large craters in this image range from 3.8-4.5 billion years in age. Many of the secondary craters form alignments or streams pointing back at Tycho like the horizontal one in the middle of the image and the one radiating away from Tycho at about 10 o'clock. The more you look, the more you'll see.
The great “walled plain” taking up the upper right quarter of this image is Ptolemaeus (158km dia.) with the more recent crater Ammonias (9km) prominent on its northern floor. Most of us lunar observers knew this latter crater as Lyot when we were kids. That name has now been given to a crater on the southeast limb. Above Ptolemaeus is the smaller crater Herschel (43 km) with its slumped walls and complex infilling. Then below is Alphonsus (121km) sporting dark haloed craters on its floor. The crater Davy is the shallow 21km diameter crater near the inset image with Davy A (15km) on it's southeastern (lower right) wall. Catena Davy can be seen as a string of craterlets some 50km long, just left of center to the northeast of the crater on the floor of the crater Davy Y (70km). The inset (spacecraft) image shows some of the craterlets in the chain near the eastern wall of Davy Y that were named in 1974 during mapping of this area. Their sizes are:
All of them can be identified in the larger image. This catena is cited as an example of an impact of a tidally disrupted body, similar to the SL9 impact on Jupiter, but because of the much slower rotation of the moon they occurred much closer to each other and make a handy scale for measuring resolution on the Moon!
Sunrise on the Aristarchus Plateau is always a thrilling sight whether in your first 60mm telescope or a 400mm cannon! The eye-popping crater Aristarchus (41km diameter) in the center of this image, is the brightest crater on the moon and at 175 million years old, a Jurassic Crater, it's one of the younger ones. Some dinosaur had a front seat to a spectacular impact show! Notice the nice terracing on the interior wall of this crater. Most of the Plateau is in shadow here. Aristarchus itself is in the southeast corner. You can see the east side of the Plateau going north from Aristarchus. Above and to the right of Aristarchus is the arc of the partially flooded Prinz (49km) and the beautiful Rimae Prinz just above. Immediately above the north rim of Prinz is the odd crater Vera. It is the south end of one of the rimae that you can see running north a little further to the left or west of Prinz. In among the Prinz Rimae is the small crater Ivan (5km), a challenge for a 3" telescope. Then further north and running off the image are the Montes Harbinger, just the tips of what must have been a magnificent mountain chain before they buried by the Imbrium basalts.
Directly above Aristarchus as you head up the east side of the Plateau, is Vaisala (9km) and some more very interesting (unnamed) rimae. Below and left of Aristarchus is the shadow filled Herodotus (36km) and the very interesting sharp ridge that runs along its eastern wall up to the big crater. There is an isolated bright spot deep in the shadow to the left. When I saw this I went to other images of this region taken this night. It was persistent but there was nothing there in my Virtual Moon Atlas so I checked on LROC QuickMap. Within a couple minutes I had determined that this is the tip of Mons Herodotus some 120km north of its namesake crater. Amazing how bright it is!
About the same time you see Kepler and Gassendi on the terminator you will find this keyhole shaped crater in the south. Hainzel (70km dia.) is the southern lobe of this figure-8 shaped feature that consists of 3 craters. The northern beautifully terraced lobe is Hainzel A and in the shadow side (east) of Hainzel itself is Hainzel C who's west wall can be seen on the floor of Hainzel. This is a very identifiable feature making it a landmark for exploring this region. To the right of Hainzel is a small crater Epimenides (27km). South of this crater is a similar sized crater, Epimenides B (26km) with a curious bulge on it's floor. North of these is a small mare, Lacus Timoris that winds its way east from Hainzel. Note the nice rima that proceeds north from Hainzel A into Palus Epidemiarum near the crater Capuanus (61km) at the top of the image. You can see one of its 3 domes on the floor of that crater.
Below Hainzel is the large crater Mee. It is perhaps the oldest formation in this image going back to Pre-Nectarian times 4.55-3.92 billion years ago!
In the wide channel between Oceanus Procellarum and Mare Imbrium, from Aristarchus to Mairan, are scattered some interesting features worthy of scrutiny. Here you can see Aristarchus (41km diameter) in the lower left corner and Mairan (also 41km) at the upper edge. The diameter is where the similarities between these two ends. Aristarchus the highest albedo of any crater on the visible disk of the Moon. It has been the site of many reports of transient events ever since the time of William Herschel who believe this to be an active volcano, now known to not be true. It is also very young at 175 million years old. Above Aristarchus is a arc open towards the bright crater. This partially flooded crater is Prinz with the Montes Harbinger sparkling in the early morning light farther on. The crater Kreiger (22km) is filled with shadow to the left or west of these mountains. To the east are two more craters in Mare Imbrium. The larger is Delisle (26km) and south of it is Diophantus (19km). Working our way north and west (left) from Delisle we come to a small crater Gruithuisen (17km) (pronounced Grooth-wee-sen) and above it The three odd shaped mountains the upper two of the trio are Mons Gruithuisen Delta on the right and Mons Gruithuisen Gamma left. These are two large lunar domes formed from the upwelling of magma (lavas) from cracks in the lunar surface at some time in the past. Gamma has a small near-central pit on its summit as well not seen here because of shadow. We end with Mairan, north of these domes.
My favorite mountains on the moon are the Montes Caucasus. Seen here as a triangular shaped patch of mountains dominating the right half of this image. The curious large crater at the top middle of the range is Calippus (34km) showing much post impact slumping and infilling. In the upper right corner is most of the large lacus-like crater Alexander (85km) partly cut off by the right edge of the image. Below Alexander on the mare you can just see the dark thread that is Rima Calippus. In the middle of the mountain range is a large flooded east-west pass that may delineate a fault. This pass opens to the west towards the very non-round, some call polygonal, crater Theaetetus (26km). Further south the peaks are more flooded with only their tips showing until at the southern point of the range is the beautiful unnamed "S" shaped ridge.
Just to the west of the mountains is the crater Cassini (60km dia.) seen at the top middle of this image sitting in the unofficial Palus Nebularum portion of Mare Imbrium. Inside Cassini are two distinctive craters, the larger being Cassini A (17km) and Cassini B (9km), There is also an interesting pair of rimae on the floor of Cassini roughly concentric with Cassini A making this crater very identifiable. Going farther to the west we see the isolated grand peak Mons Piton rising 2250 m above the Imbrium plain. South of this is the large crater Aristillus (56km) and then Autolycus (41km). In the middle bottom part of the Rima Fresnel system can just be seen.
Apollo 17 was our last manned mission to the moon. The first two Apollo missions were the "safe" ones: go to the moon, land, the astronauts do a little exploring and "returning them safely to the Earth." Apollo 11 had 2.5 hours of EVA (Extra Vehicular Activity) during which time they collected 21.55kg of samples. The EVA time and collections increased for each successive mission culminating on Apollo 17 at just over 22hours in 3 EVAs on the surface with a total collection of 110.4kg of geologic samples. This last mission was the only mission with a professional geologist, Harrison Schmitt a member of the crew.
In this image we can see the landing site for Apollo 17, in the Taurus-Littrow Valley, marked with a "o" above center. Immediately above that marker is what was called North Massif and below it, brighter here, is South Massif that define the valley. All the EVA activity with the rover took place between these mountains, an area just a bit larger than the marker itself. The large shallow crater above this marker is Littrow (32km dia), and below and a little to the right is a similar sized but deeper crater Vitruvius (31km). To find the landing site locate these two craters and then look for the line of 4 mountains between them. The mountain chain points right to the crater Gardner (19km) and above it is Miraldi (41km). At the bottom of this image is the crater Plinius (44km) partly cut off by the edge of the image and above it Dawes (19km). There is much more to see here but the point is that you can take the average amateur telescope and easily see the area explored by our astronauts on Apollo 17!
This last lunation had a night where Mare Australe was very well displayed. This is a mare unlike others, consisting of a collection of craters with flooded floors rather than a broad expanse of basalts like Imbrium and Humorus. In the middle of this collection of black spots is one larger one, the crater Lyot (145km dia.). In the early 1960s I learned that Lyot was the prominent 9km crater on the floor of Ptolemaeus, now known as Ammonius. I've labeled Lyot as a reference point. Above Lyot is a very circular dark crater half the size of Lyot. This is Oken (75km) with the bright crater Hamilton (60km) between it and the limb. Above these two is another dark patch, Marinus (also 60km). At the very top limb of this image is the dark floored crater, Abel (117km).
Going back to Lyot we see a very dark crater on the western edge of this mare, Brisbane (46km). Further out from this in the same direction we see a nearly vertical gash. This is end of Vallis Rheita. Lastly, on the far lower left end of this field of dark floored craters, is an isolate one Hanno (58km). You can hunt out more features using some of the online atlases like the 1:1 Million-Scale Maps of the Moon at: https://planetarynames.wr.usgs.gov/Page/Moon1to1MAtlas
Somewhere near the large crater Fra Mauro are two golf balls. That is what most people remember best from the Apollo 14 mission, the third manned mission to land on the moon. Not only did Commander Alan Shepard hit those two golf balls during over 9 hours of EVA (Extra Vehicular Activity) but they also brought back a then record 42.8kg of rocks. The landing site was north of the crater Fra Mauro (99km dia.) seen here just left of center with a small central crater, Fra Mauro E (4km) in the center and is marked with a small circle in the fairly rugged terrain (compared to the previous two landing sites of Apollo 11 and 12).
Below Fra Mauro are two craters, one with two large rimae almost at right angles to each other. This is Parry (49km) with the Rimae Parry and to the left of it is Bonpland (61km). These three are old craters, maybe over 4 billion years old. Below these ancient rings is a smaller, obviously younger crater, Tolansky (14km) about a billion years younger.
At the bottom of the image is another ruined crater, Guericke (60km). To the right of Guericke is a very young crater Kundt (12km) possibly less than a billion years old. Before leaving this scene look to the upper right of Fra Mauro and the odd mountainous terrain there. The largest mountain, shaped like a spearhead, is Fra Mauro Eta which has a small crater Fra Mauro R (3km) on top (unfortunately in the shadow in this image). It was speculated, at one time, that this might be a volcanic vent but Lunar Reconnaissance Orbiter Camera (LROC) QuickMap imagery shows it to be little different from surrounding craters of similar diameter.