The Moon

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The Moon, being truly local in galactic terms, is our best opportunity to study another world in intimate detail (Figure 5.1). It is also a prime candidate to form a long-term relationship with from suburban locations, because it is completely accessible from what would be some of the worst conditions for almost anything else. Often flying high in the sky, it is well-placed much of the year so as not to be obscured by city buildings and other horizon blockers.

In order to enjoy spending time with our nearest neighbor in space, you will need a good, preferably photographic, lunar atlas to gain an easy comfort level during observations. Even though I have used Atlas of the Moon by Antonin Rukl extensively, I do not necessarily recommend this classic. This, in spite of its finely drawn viewing maps, which are probably the finest achievement known in lunar cartography. I have two primary objections: first, the maps are printed with north up, which makes referencing and reading at the telescope something of a test for patience. Secondly, the book uses a strange logic that sets out the progression across the lunar surface not in accordance with the phases. This again makes for less than total user friendliness, and easily brings about confusion. In any event, photographic atlases would seem to be a markedly better option for us. Some decent choices are available, but as of yet, I have not found the perfect one. I suggest that you make a comprehensive search of what is available in order to see which atlas seems closest to your needs.

Figure 5.1. The crater Deslandres and environs as recorded by CCD video camera.

Meantime, a classic from the 1960s is still in print, and is probably still the amateur's best guide overall: The Hatfield Photographic Lunar Atlas, edited by Jeremy Cook (published by Springer). The primary weakness of this near timeless work from pre-Apollo times would seem to be the photographs. While they are fine amateur astrophotographs for the time (from the 1960s) and are logically laid out, they are nevertheless inferior to the images that can be obtained with today's means. The similarly famous work and classic, The Moon, by H.P. Wilkins and Patrick Moore, while again a remarkable feat for its time, is not nearly as useful a guide by comparison. This is especially apparent since the line drawing cartography, so painstakingly carried out, has been completely superseded by space age imaging techniques. It is actually quite a difficult work for most people to use.

There is no denying that a lifelong and detailed study of the Moon will provide near-endless enjoyment, and its role should always feature prominently in any suburban dweller's viewing. The larger aims of this chapter, though, are not only to lead you to some magnificent lunar sights, but also to some of those smaller ones, which may reveal ways that the Moon can help expand the eye's seeing power and test our equipment. All of

Figure 5.1. The crater Deslandres and environs as recorded by CCD video camera.

Figure 5.2.

Daybreak at Aristoteles and Eudoxa.

the images were recorded in real time, directly to computer hard drive and are presented essentially unprocessed. For the most part, they were recorded in unexceptional suburban viewing conditions of air turbulence at sea level, as low an altitude as a city can have! Equipment used was my JMI NGT-18 and Astrovid 2000 CCD video camera, the same one that couples to the Collins I3 Piece intensifier for imaging deep space subjects. As simple images, they are nevertheless quite impressive (Figure 5.2 and 5.3), compared to what used to be available only photographically.

The ease with which these images can be obtained is also quite remarkable, although of course, they do not quite compare with true CCD imaging. In overall appearance, they represent the lunar surface very well, except in the resolution of the very finest details.

Figure 5.3. Nightfall on the lunar limb and the crater Gauss.

Figure 5.2.

Daybreak at Aristoteles and Eudoxa.

Figure 5.3. Nightfall on the lunar limb and the crater Gauss.

Viewed live, minutia are resolved diamond-sharp, and appear almost three-dimensional, something apparently impossible to represent in any type of recorded telescopic views. Today's best in astronomical video gear does a remarkable job nevertheless (Figures 5.4 and 5.5). The finer features discussed in my review of lunar sights may not be apparent on all of the images, especially in printed form, but at least the specific areas on the lunar surface are clearly represented for examination. It is worth pointing out that although they were taken through 18 inches of aperture, the images actually approximate resolutions of smaller apertures, owing to the loss of fine detail in the relatively simple imaging process I use. These images may be a helpful reference point in considering visual expectations with telescopes in the 4-10-inch range, and will give you a very good impression of the viewing experience through such moderate apertures in merely fair suburban skies.

Figure 5.5. The bright ray crater Kepler.

Figure 5.5. The bright ray crater Kepler.

I make no apologies for succumbing to the temptation to include many of my favorite lunar sights amongst those presented here, even though they may have been more than adequately covered in other volumes. This sampling is perhaps just a little more personal, particularly because the images were recorded with the unique illuminations of those very moments of the lunar day as I witnessed them.

Petavius (23.3°S, 60.4°E) (Figure 5.6). Long a favorite of mine, this crater has associations that hark back to my earliest days of astronomy. With its celebrated cleft, a striking feature running from the central peaks to the perimeter, Petavius was one of those lunar landmarks that I strained to discern through my tiny telescope of childhood. With a slightly less modest instrument, you will easily be able to see the vast rupture across the crater floor, splitting the surface decisively, and maybe discern other smaller clefts as well. The majority of detail will be quite clear at moderate apertures, although larger telescopes will naturally reveal significantly more.

Figure 5.6. Petavius.

Rheita Valley (42°S, 51°E) (Figure 5.7). One of a few great gashes on the lunar surface, this valley was most likely gouged out by enormous material(s) ejected during the impact that created the Mare Nectaris. Also crossed by various craters from a later date, it lies in a very rugged region and can easily be missed by the casual observer. Easily overlooked is the full extent that it travels, although this clearly shows on the video image here.

Figure 5.7. Rheita Valley.

Figure 5.8. Messier.

Messier (1.9°S, 47.6°E) (Figure 5.8). A striking feature on the Mare Fecunditatus, this is actually a triple crater lineup, with ejected material shot far out in a double ray. The dominant crater almost obliterates an earlier crater, as well as a third and similar-sized crater ahead of it, just detectable in this image. It was most likely formed by a collision with a sizeable meteor striking almost parallel to the surface.

Posidonius (31.8°N, 29.9°E) (Figure 5.9). A fine and intricate network of ridges and rilles lie on the crater floor, in addition to other rocky formations. South of the crater is a raised ridge, appearing like a crumpling of the lava plain, known as Serpentine Ridge. Its height, like many similar formations, is more akin to a large sand dune than a hill, made visible to us only at times of very oblique illumination. Occasional tiny craters can be seen at points along the spine of the ridge with good conditions and sufficient aperture.

Lacus Mortis and Burg Rille (45°N, 26°E) (Figure 5.10). Not far from Posedonius lies the Lacus Mortis, actually something of a ruined and lava-filled crater of vast dimensions. The rille crossing this feature is unmistakable (easily visible in the video image in Figure 5.10 as a fine line traveling straight down), but y ^

no less striking than the great fault to the east (also easily visible here), the shadow it casts being readily detectable at lunar dawn as a broad, dark feature. Look for other smaller faults northwest of the crater Burg, but most particularly the great ridge dropping off and curving west from it. Under advantageous illumination, and with steady seeing, Burg (upper right) becomes an interesting study in itself: look for its prominent central peak, but more significantly, the huge collapse inwards of its interior walls, which once experienced landslides on a massive scale. Also

Figure 5.10. Lacus Mortis (upper right) and the crater Burg.

Figure 5.11.

Theophilus.

Figure 5.11.

Theophilus.

significant is the crater Aristoteles to the west, a structure not unlike Tycho, but without surrounding rays or a significant central peak.

Theophilus (11.4S, 26.4°E) (Figure 5.11). This is one of the most prominent features on the Moon, with towering central peaks and a complex rampart structure. It keeps company with two other striking formations, the older and less well-preserved craters Cyrillus and Catharina. Together, around first quarter, they are unmistakable landmarks.

Plinius (15.4°N, 28.2°E) (Figure 5.12). Although not traditionally one of the more famous lunar locations, Plinius is nevertheless a visually pleasing, sharply defined crater with central peak, terraced walls and interior detail, located in between the Mare Serenatis and the Sea of Tranquility. Perhaps my main interest, though, in this otherwise unlikely-to-be-favored structure betrays a little of my professional background: a rock formation to the east amid other interesting crumpled and pitted landscapes, and adjacent to the

small crater, Carrel, looks for all the world to me a lot like a very familiar musical notation - an eighth note! (I don't believe any musicians were there before the Apollo astronauts landed!) Look for it mid-frame toward the right side of this video image.

Hyginus Rille (8°N, 6.3°E) and the Treisnecker Rille system (5°N, 5°E) (Figure 5.13). Hyginus Rille presents a most interesting geological riddle, since for much of its length it comprises a chain of rimless craterlets, interrupted mid-length by the crater, Hyginus. The finest of these craterlets become more difficult to resolve, and aperture, steady seeing as well as good optical quality will pay dividends. So how did this unlikely chain of craters just happen to align into what we see? Far from being a freak of meteoric bombardment, it appears instead that the rille is probably just a collapsed lava tube, formed by systematic collapse along the length of the underground structure. To the northeast lies the wide Ariadaeus Rille, an easy sight for small telescopes, with one end visible here in the image extending into the top right corner. The spectacular and complex Triesnecker Rille system may be found immediately to the southwest of Hyginus, and east of the crater after which it is named. Viewing these intersecting and finely formed rilles immediately after dawn or just before sunset is the most significant factor in being able to resolve them successfully. They are

Figure 5.13.

Hyginus Rille and the Treisnecker Rille system.

truly spectacular and mazelike through my own telescope with only moderately good suburban viewing conditions. As probably the most celebrated rilles on the Moon, and frequently imaged by observatories since the beginning of lunar photography, even users of small telescopes will have success in revealing many of them.

Mount Hadley; Hadley Rille (27°N, 4°E) (Figure 5.14). The landing site of Apollo 15. This is one of my favorite lunar mountainous sites. Although not prominent on this video frame, Hadley Rille is not too difficult an observing test with moderate apertures, given reasonable conditions. As with other Apollo landing sights, with sufficient resolution and magnification it is possible to gain a real insight into lunar terrain, when comparing the view with photographs from the mission. For smaller telescopes, though, Hadley Rille becomes harder to resolve and trace to its full length, as it winds around the flat terrain and crater Hadley C. Look also for the prominent Bradley Rille nearby, (23°N,2°W) as well as other similar formations.

Figure 5.13.

Hyginus Rille and the Treisnecker Rille system.

Hadley Rille is likely to be in the same field of view as Archimedes (29.7°N, 4°W), Aristillus (33.9°, 1.2°E) and Cassini (40.2°, 4.6°E). These three craters make a varied group. Archimedes is a prominent lava-flooded crater with high walls, not unlike Plato in appearance, but smaller and with a paler floor color; it also has a number of small craterlets that can be challenging to resolve, but is in no way the equal of the nearby and better known Plato for craterlet counting and spurious claims. Aristillus has several low peaks in its center and is one of the well-known "ray craters", becoming more prominent with increasing lunar phases.

Alpine Valley (49°N, 3°E) (Figure 5.15a). Just east of the walled crater Plato, this most famous of lunar valleys looks like a huge gash right through the Lunar Alps. Actually, it was probably formed like many other smaller and similar valleys, as a flow of lava, and not the sort of collision its appearance tends to suggest.

Obvious with the slightest optical aid, the valley is striking during second quarter. Larger apertures combined with good seeing, even from the city, and optimum lunar morning or evening illumination, will reveal a fine rille on the seemingly level lava-flooded floor, running most of the length of the valley. (Just detectable in Figure 5.15b as a fine bright thread, this feature is readily visible in 18 inches; it will probably also show in some lesser apertures.) Low left of center lies the ruined crater formation Cassini.

Ptolemaeus (9.2S, 1.8°W) (Figure 5.16). No chapter of the Moon would be complete without drawing attention to this grand crater. Long a favorite target of amateur astronomers, it has regularly been the focus of reported "volcanic" activity, although such claims have never been substantiated. Its floor, as with many crater basins, was long ago leveled out into a plain by lava

flow, and features many small craterlets and almost-obliterated earlier crater formations. Nearby are the no less interesting craters Alphonsus and Arzachel (with its marvelous central peak), both also part of the volcanic myth. These three craters become prominent just after first quarter.

Figure 5.16.

Ptolemaeus.

Straight Wall, Birt Rille and Pitatus (21°S, 9°W) (Figure 5.17). The Straight Wall remains one of the most celebrated features on the Moon for its great length and height. Approximately 60 miles long and presenting a face around 800 feet high, it must be an awesome sight from ground level; nothing close to these dimensions exists on Earth. Immediately west of this grand fault lies a test of vision and equipment, Birt Rille, quite a fine feature (barely visible here). However, an even finer test is the small craterlet at each end of it, which moderate apertures should reveal when our suburban atmosphere allows. Also look for shading variations within crater Birt; these will be visible as subtle irregularities, and are not usually commented upon. I have seen them clearly. Pitatus, to the east, is striking for its fine rilles and complex ramparts.

Plato (51.6°N, 9.3°W) (Figure 5.18a). This vast and famous crater is another example of one which has been partially filled in with a dark lava flow from a later time, forming a smoothly textured floor. A favorite target for amateur astronomers, there are at least five reasonably prominent craterlets to look for on this

wide plain. Many more have been observed and counted by multitudes of Moon watchers over many generations; because of the exact number and location of the craterlets, Plato was in the past amongst the amateur observers' most highly watched and controversial lunar sights. Much of the controversy over these craterlets has been settled by lunar orbiters. The formation itself is so striking in appearance, regardless of the phase of illumination, that it stands out as a dominant feature on the lunar surface; small craters can be seen as bright dots even at full moon. Do not miss nearby Mts. Piton and Pico (Figure 5.18b), standing in splendid isolation on Mare Imbrium.

Tycho (43.3°S, 11.2°W) (Figure 5.19). One of the foremost lunar ray craters, the impact that formed Tycho spewed out material over many hundreds of miles, further than any other crater of its type. This type of crater grows in prominence towards full moon, none

Figure 5.19. Tycho.

more so than Tycho; in this instance an otherwise only moderately imposing crater becomes very bright and its extending rays seem to dominate the entire lunar landscape.

Clavius (58.4°S, 14.4°W) (Figure 5.20a). This massive, grand and prominently placed crater must be familiar to anyone who has spent any time at all observing the Moon. It is known to many others as the site of the fictional lunar base in Arthur C. Clark's 2001, A Space Odyssey. it reveals a multitude of details, the best-known being a chain of ever-diminishing inner craters,

Figure 5.20. Clavius in a sunlight and b at dawn.

Figure 5.20. Clavius in a sunlight and b at dawn.

Figure 5.21. a Morning light on Eratosthenes. Note the chains of craterlets below - these are ejecta pits from the formation of nearby Copernicus (just appearing at dawn, bottom center); also note the large lava-filled crater Stadius, center right. b Eratosthenes just 24 hours later.

Figure 5.21. a Morning light on Eratosthenes. Note the chains of craterlets below - these are ejecta pits from the formation of nearby Copernicus (just appearing at dawn, bottom center); also note the large lava-filled crater Stadius, center right. b Eratosthenes just 24 hours later.

evenly spread across its floor in an arc. Clavius is one of the largest crater formations on the entire lunar surface, though not the largest, as some comment. Its dominance is striking even though its walls lie almost entirely below the surrounding rugged lunar plain. You will probably appreciate observing it under many lunar illuminations (Figure 5.20b), not only for its spectacular nature, but also because it lies in some of the most rugged and interesting terrain on the lunar surface.

Eratosthenes (14.5°N, 11.3W) (Figure 5.21). This striking crater lies in the vicinity of the great ray crater Copernicus, but precedes it in the arrival of dawn. The video image in Figure 5.21a was taken shortly after daybreak, and at the lower center can be seen the first sign of light on the eastern edge of Copernicus itself. Eratosthenes is no less notable for terraced walls and central peaks than its grander and better-known close neighbor; it also forms a kind of marker for the western extreme of the Lunar Apennines. Like some other striking formations, it is also significant for its great range of appearance under different illuminations, and it graduates rapidly from a highly striking formation to one that is hardly visible in only a very few days.

Figure 5.22.

Copernicus.

Copernicus (9.7°N, 20°W) (Figure 5.22). One of the most spectacular of all lunar formations, not only because of its dramatic structure and visual placement, but also because it is one of the Moon's most prominent ray craters. Copernicus' massive walls rise over 3,000 feet above the surrounding terrain, with much evidence of landslides on their interior. The floor lies well below the lunar plain by as much as 7,000 feet, and a series of central peaks rise from it to a height of nearly 4,000 feet. Surrounding the crater lies the inflated lunar crust, as well as extensive radiating debris and craterlet pits from what must have been the cataclysmic impact long ago which formed it. It must have pushed upwards enormous amounts of material from deep below the surface, which finally rained down on the surrounding plain.

Gassendi (17.5°S, 39.9°W) (Figure 5.23). This ruined crater is quite a magnificent formation, so much lava

having filled its interior that it produced a circled plain, riddled with clefts and mountain peaks. On the north side, a more recent collision created a smaller crater which pushed the wall in and part of the floor upwards. Be sure to spend time with nearby Mare Humorum. Its extensive ridges, as well as rilles such as Doppelmayer and Hippalus rewarding the time you will have spent.

Schröter Valley (26N, 51°W) (Figure 5.24). A curious formation, Schröter Valley takes on the appearance of a cobra, as it widens and culminates in the crater Herodotus, the cobra's head. Depending on the lighting, the chiseled landscape to the north can give the illusion of a twin valley in the opposite direction. The visual test is to see how far you can trace out the real valley, which narrows along its length towards the cobra's tail. East of the valley is the extraordinary ray crater Aristarchus; its sloping sides, bright interior, and central "bump" make it a striking formation.

Also in the vicinity of the valley (just southwest), and likely to be in the same field of view, is a typical, but sometimes frustrating lunar rille:

Marius Rille (17°N, 49°W). This rille is one of the better examples for testing visual acumen as well as equipment. Thin and winding, it will demand keen viewing skills and equipment of at least moderate aperture. As a much quoted test, the challenge, as with others, is to see its entire length. The only chance to do so will be shortly after lunar sunrise or sunset, when contrast will be at its best. (It is not difficult with 18-inch aperture.)

Schickard (44.4°S, 54.6°W) (Figure 5.25). A vast, partially lava-flooded crater with walls and floor pockmarked by small craterlets. After first quarter this is a mighty feature low on the south limb. It is located in one of the most rugged and highly cratered areas of the Moon, and will be striking to view under many vari

Figure 5.25.

Schickard.

eties of illumination. The view here was taken at dawn on the region.

Many larger areas of lunar landscape will provide constant visual engagement for the amateur observer; these are not necessarily specific features, but regions that by their very natures demand attention. Shortly after dawn the region adjacent to the Mare Frigoris (62°N, 0°) (Figure 5.26) is one such place. In my view,

Figure 5.25.

Schickard.

Figure 5.26. Mare Frigoris.

a Promontorium Laplace and b Harpalus.

a Promontorium Laplace and b Harpalus.

Figure 5.27.

Figure 5.27.

there is little like this barren region anywhere. Stark and other-worldly, with its deep shadows, the area is punctuated with bright craters and rays.

Another wonderful scene is nearby Sinus Iridum. On the eastern extremity of the surrounding "wall" is a tall feature, Promontorium Laplace. After dawn it casts a large, pointed shadow over the corner of the plain (Figure 5.27a). Also look for the striking crater Harpalus, to the west (Figure 5.27b), which seems to show a double wall and flat floor, like a woven basket in appearance; (sunrise has not yet taken place on it in Figure 5.27a, right; see instead Figure 5.27b). To the east (top center, Figure 5.27a) is an unusual and almost straight isolated mountain range, the Recti Mountains (45°N, 34°W). This feature lies at the western edge of Mare Imbrium, a vast lava plain with isolated jutting peaks and expansive creases and crumplings, south of Plato.

Ghost craters: in the region of another striking walled ray crater, Bullialdus (on the left in Figure 5.28), is a varied array of mostly lava-filled remnants of craters. These old structural remains, almost completely hidden now, were formed and almost obliterated before the creation of the region's more complete crater structures. Similar formations can be found across the lunar surface, but this remains one of the areas of greatest concentration (20.7°S, 22.2°W).

There are, of course, almost limitless other sights on the Moon that could be included here, and many more tests for the eye and telescope, but since this is not

primarily a textbook or an atlas on the Moon, it was necessary to call a halt somewhere. As a complete study in itself, lunar observing fills volumes, so I strongly recommend that you avail yourself of at least one major book devoted exclusively to it. It is the only celestial object which reveals itself to us so readily and so fully. Perhaps its strongest card for us in the confines of the city is that it is completely unaffected by city light and air pollution. For suburban or urban viewing it can be a salvation; since it can be counted on as a regular sight in the sky there are still those who scarcely observe anything else. A downside is that when sky conditions are perfect for deep space observing, there is no guarantee that the Moon won't be high in the sky, and even full phase, to wipe everything else out - the ultimate light pollutant!

Figure 5.29. Views like this, taken just before first quarter, almost give us a sense of being in orbit!

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