Twentyoneday Moon

What is the most conspicuous feature of the moon tonight? Aristarchus is the brightest, but through a small glass it is a dazzling spot with a tail and little more of interest. The Kepler splash pattern is brilliant, but the crater itself v irtually is lost in the glare. Copernicus and Tycho still are conspicuous, but their luster is fading. Some of the large craters of the south near the terminator stand out prominently because of contrast between their black interiors and brilliant walls and crests. Plato and Grimaldi attract the eye because their floors, while well illuminated, are made of dark lava and their surroundings are bright. Picking the nux& conspicuous object on the face of the moon is not just difficult; it is impossible. On what basis do we select "the most" unless it is measured in tons, bushels, dollars, or some other definite unit of quantity? As soon as we apply the term to judgments in questions of appearance or relative evaluations in such vast, intangible realms as human achievement, leadership, contribution, and service, our measuring instruments become subjective and our data inadequate.

Having shown that it is impossible to pick the outstanding lunar feature, I now shall call attention to one of the outstanding features. The great arc of the Apennines continued, after interruption, by the Caucasus Mountains is a magnificent sight tonight. The foothills are not so bright as they were a few nights ago, but the broad faces of the higher mountains, rising to the crest of the range on the Mare Imbrium border, are in full sunlight, and once again thev shine with a sort of super brilliance. Tomorrow night, at about the time the moon rises, the standard terminator will begin its 40-hour journey across the Apennines, and by observing time the following night it will have crossed most of the mountains and reached the narrow tail between the main body of the range and Eratosthenes. If the current lunation happens to be out of step with my average or most probable lunation by as much as 6 to 12 hours, you may be able to observe when the terminator is not far from the center of the range. At such time the mountains, because of their great height, easily are seen extending at least 100 miles beyond the terminator. Concerning the range. Webb writes: "Its projection into the dark side, which may be seen without telescopic aid, probably gave rise to the early idea mentioned by Plutarch [first century, a.d.], that the moon was mountainous." The standard terminator for the seven-day moon bisected the Apennines and revealed the same interesting phenomenon, but I did not mention it at that time, preferring to introduce the Apennines the following evening when the whole range came into view. Remember to look for the range on the terminator, and sec if you agree with Webb that it is visible to the naked eye insofar as its bright peaks extend onto the dark side.

Tonight Mare Tranquillitatis is gone, and only half of Mare Serenitatis remains. As we trace the terminator across the latter, we may be able to see, about % the way from the south to the north shore, Class 1 bessel, 10 miles in diameter and 5200 feet deep (Fig. 11). Its interior, of course, is black, but the east and west walls are bright. Perhaps also we can make out a faint, light ridge running north from the little crater. It swings slightly to the east for 45 miles, disappears, continues north after a break of some 25 miles, and ends 120 miles from Bessel. If the terminator still is several Bessel widths east of the crater, look for a second ridge curving gently to the southeast of Bessel about 90 miles and reaching almost to the shore.

Just west of the terminator, on the scuth shore of Mare Serenitatis, Menelaus remains conspicuous even though most of its interior is black. On either side of it the Haemus Mountains show well as they delineate sharply the south border of the mare. Across the mountains, two Plato lengths west of Menelaus, larger Manilius shines brilliantly. Tonight less than V2 its interior is dark, but by moonrise tomorrow the sunset line will have crossed it and advanced on Mare Vaporum to the west. As we look again at one of the maria, note that they do not appear as dark as they did around full moon. Each night their contrast with the bright uplands will diminish, and when we reach the crescent stage very little intensity difference will remain between plain and highland.

West of the Caucasus, Aristillus and Autolycus are prominent, their fully-illuminated floors framed by bright east and black west walls. Northeast of the Caucasus, the terminator has reached the foot of Eudoxus' outer east wall and the foot of Aristotle's inner east wall. Both appear as large black pits with brilliant east walls. Near the middle of the Caucasus, southwest of Eudoxus a little farther than the distance of Aristotle to the north, distorted, pentagonal, Class 1 calippus appears (Fig. 8). With a black interior outlined in white, it is 19 by 21 miles across, 9800 feet deep, and in this light it bears close resemblance to a square. It is partly covered by the shadow of a mountain near its west wa!l which, according to Goodacre, rises 18,000 feet, a measurement made about a century ago but in good agreement with Army Map Service's elevation of 17,400 feet above the Imbrium plain.

On Mare Frigoris, about two Plato lengths northwest of Aristotle, the small, young crater pbota-coras, 12 by 14 miles across and 6goo feet deep, may be seen as a black dot (Fig. 8). One Eudoxus length northwest of Protagoras is the white dot of large Class 1 archytas, 20 by 22 miles across and 7500 feet deep (Fig. 9). Continuing in the same direction one Plato length from the last we come to similar Class 2 ttmaeus, 20 miles in diameter and 7400 feet deep (Fig. 9). There should be enough contrast to bring out huge william bond, tangent to Timaeus on the northeast and fully illuminated (Fig. 9). It is bounded by four nearly straight walls laid out in the apparent shape of a diamond 100

FIGURE 49. Late afternoon in the heavily cratered region near the southeast limb. Bacon and Bacon a exhibit approximately hexagonal outlines, the most prominent linear sections of which run northeast—southwest. a similar alignment is shown by many other craters here, particularly by Mutus and its smaller neighbors to the north and northwest. In the lower right section of the picture, linear crater walls, chains small craters, and linear depressions are so numerous that they seem to trace out a series of parallel northeast-southwest lines across the surface. Such

FIGURE 49. Late afternoon in the heavily cratered region near the southeast limb. Bacon and Bacon a exhibit approximately hexagonal outlines, the most prominent linear sections of which run northeast—southwest. a similar alignment is shown by many other craters here, particularly by Mutus and its smaller neighbors to the north and northwest. In the lower right section of the picture, linear crater walls, chains small craters, and linear depressions are so numerous that they seem to trace out a series of parallel northeast-southwest lines across the surface. Such lines are called lineaments, and they mark the direc tion of breaks or faults in the moon's crust. Other '■neaments. less conspicuous here, can be traced north-south and northwest—southeast. The lineaments oonstitute the grid system or global cracking pattern ^o moon. Similar patterns are found on earth in the Places where erosion has not obliterated them, and y aro expected on other planetary bodies as well.

miles across arid rising at one point to a height of 9800 feet. The wall on which Timaeus stands is low, broken, and inconspicuous, but the other three should be seen. The southeast and northwest walls, bright with dark edges, are double over most of their lengths, and through binoculars they resemble parallel bulldozer cuts. Actually, the enclosure is a pentagon distorted into a close approximation to a rectangle 90 by 107 miles on the sides. Just north of William Bond is the thin ellipse of bright-floored Barrow with the young intruder Barrow A in the southwest wall. Barrow A, dark except for its east crest, probably is merged with the strong shadow that covers the west quarter of Barrow's floor. North of Barrow a distance equal to approximately its separation from William Bond, or half its separation from Archytas, Class 1 scoresby, 35 miles in diameter and n,800 feet deep, may be seen. Although it appears as a tiny black ellipse tonight, its outline is enhanced by a bright northeast crest. Tangent to Scoresby on the northwest is what appears to be another weak dark crater of about the same length but definitely wider and broader at the ends. It is an overlapping pair of craters older than Scoresby. The south one is challis and the north one is main. Their respective diameters are 37 and 32 miles, and both have walls that rise 9200 feet above the floor. At the center of Main we still are nine degrees from the north pole, but let's not push our luck any further tonight. If there is a large negative libration in latitude we are not likely to get this far north before the craters become flat streaks and lose their identities. So let's turn around and head for the southern hemisphere.

One Iridum length south of Menelaus, and an equal distance southeast of Manilius, the horseshoe outline of ancient Julius Caesar shows well, and at least one of the giant parallel "claw marks" in the area can be traced along its northeast wall. Two Plato lengths southwest of Julius Caesar, Agrippa stands out in the midst of rugged territory, and so does the smaller Godin just south of Agrippa. Their interiors are half black, but their inner east walls are brilliant. Midway between Julius Caesar and Agrippa, the ariadaeus rill may be traced in an approximately straight east-west line for 145 miles with a small telescope (Fig. 10). You might spot it through your binoculars, but it is an extremely difficult test. West of it lies the equally difficult hycinus rill. About one Humorum length south of Julius Caesar, at the terminator, Delambre is seen for the last time as a light-bordered black ellipse. Between Delambre and Godin is an unused tentative touch down site, but in the highlands 130 miles south of Delambre, Apollo 16 landed on April 21, 1972. One Plato length southwest of Delambre are two similar but smaller craters. The southeast and stronger one is Class 1 taylor, 21 by 31 miles across and 8100 feet deep. The northwest one is older, deformed taylor a, 20 by 25 miles across and 10,000 feet deep (Fig. 50). Taylor, near the terminator, is a small black pit ringed in light, but Taylor A doesn't look like a crater tonight. It appears more like a valley bounded by bright mountain walls.

Southwest of Delambre, approximately the Copernicus-Kepler distance, lies Albategnius, the strongest of the several huge craters in that area. Its central peak may be seen, and the crater can be identified by its intruder Klein which occupies most of the floor between the peak and the southwest wall. Just north of Albategnius is the larger but less-prominent Hipparchus. Its intruder, Horrocks, on the northeast floor shows well. The contrast between the walls and floor of Hipparchus will increase considerably in the next few hours as the sun goes down. On the south wall of Hipparchus, Halley and its slightly smaller neighbor Hind also show well. Again you might check your resolving power by looking for smaller Hipparchus C just northeast of Hind and even smaller Hipparchus L northeast of Hipparchus C. The four are about equally spaced, but the last two are difficult.

Note the distance from the south rim of Albategnius to the north rim of Hipparchus (or to Horrocks). That distance east of the south rim of Albategnius we should find Class 1 abulfeda, 40 miles across and 10,500 feet deep (Fig. 50). Its flat floor, sharply bordered by a broad, bright east wall, is only half in shadow, but the sunlit half appears dark also. In the telescope it resembles a piepan. Just south of its east wall is similar but smaller and older Class 2 almanon, 31 miles in diameter and 6600 feet deep (Fig. 50). Southwest of Almanon, a distance equal to its separation from Abulfeda, we see Class 1 ceber, 27 miles in diameter and 9600 feet deep (Fig. 50). Because of its greater depth and bowl shape, most of its interior is black even though it is a little farther from the terminator than Almanon, more than half of which is still illuminated. Continuing southwest of Geber, not quite so far as the last step, we find a strong pair of tangent craters. The south one is irregular, Class 1 azophi, 29 by 34 miles across and 11,200 feet deep. Its companion on the north is similar Class 1 abenezra, 25 by 28 miles across and 10,500 feet deep. While both belong to the youngest class, the former is oldef since its wall is overlapped by that of the latter. Southeast of the last three craters and south of Al-manon may be seen the much larger and very much older Sacrobosco, most of which is now in darkness, with its bright east wall close to the terminator. A fcw hours earlier the three large floor craters still were visible, and they marked the eyes and mouth on the face of a startled monkey, inverted as seen through binoculars.

Southwest of Azophi and Abenezra, about one Humorum length, is the much larger and more conspicuous pair Aliacensis and Werner, fully illuminated except for their west walls. Through binoculars the last pair closely resembles a doubly-enlarged image of the first pair since the relative sizes and orientation are about the same for both pairs. Midway between the two Class 1 pairs we see a more widely separated north-south pair of Class 2 craters apparently connected by a bright ridge. The ridge is the west wall of a much older, inconspicuous crater wedged between the two, and it is also the east wall of a much larger ancient crater upon which both have intruded. The larger, southern crater of the pair is apianus, 38 by 44 miles across and 10,100 feet deep. The north one is playfair, 27 by 30 miles across and 7800 feet deep. Both have smooth, flat-appearing floors which remain fully illuminated tonight. East of Apianus and south of Geber, ancient, distorted pontanus may be distinguished from its jumbled and broken surroundings. It is 35 by 38 miles across and 6900 feet deep, but its outline is more nearly square than circular (or elliptical in projection). One Albategnius width south of Pontanus is slightly smaller but more prominent Good-acre. The larger and more conspicuous crater there, the north wall of which has been partially destroyed byGoodacre, is Gemma Frisius. Its broad east inner wall shines brilliantly near the terminator.

One of the more conspicuous features is the great crater Maurolycus near the terminator and one Iridum length south of Gemma Frisius. Its broad bright inner east wall is the chief highlight of the whole southern continent tonight, outshining by far •be celebrated Tycho. The rough arc of the west wall is outlined well by the shadow which covers most of the floor and forms a backdrop for the wight central mountain. Perhaps you can resolve me peak through your binoculars. Tangent to Mau-Jwycus on the southeast is a large, bright-bordered ack ellipse that merges with the shadows to the "°rtb- That is Barocius. A few hours earlier we have been able to resolve its northeast wall •ruder Barocius B, since its complete crest was then in sunlight, the west half a delicate, bright semiellipse separating the black interiors of the two craters.

Nearly tangent to Barocius on the southwest is the similar but less prominent Class 2 clairaut, 37 by 59 miles across and 9900 feet deep (Fig. 51). Like Barocius, its true outline is elliptical, or, rather, it was before several subsequent impacts broke and distorted its walls and floor. Tonight it resembles a black bean near the terminator, and you may be able to make out the intruder on its south wall— clairaut a, 22 by 24 miles across and 4900 feet deep. The Barocius-Clairaut line, extended southwest by its length, reaches more normal and more prominent Cuvier which shows well, about V4 bright and more than % black. Tangent to Cuvier on the west is that curious Heraclitus-Licetus enclosure that appears to consist of two craters connected by a broad double trench. It shows well with broad walls bright on the east and black on the west. The bright ridge down the center of the trench may be visible although it casts a very narrow shadow as yet. North of Licetus and west of Maurolycus may be seen large Stofler with its southeast wall destroyed and replaced by Faraday which in turn displays two overlapping craters on its southwest wall. The group is not prominent tonight. The black west wall of Stofler is narrow, but the Faraday west wall shadow is much stronger and it merges with the half-black intruders on the southwest wall. It is around this phase that the whole combination resembles a sketch of a baby hamster when viewed through a telescope. Tangent to Stofler on the north is the smaller Class 3 fernelius, 41 miles across and 6200 feet deep (Fig. 51). It is distorted and elongated by fernelius a in its west wall, a crater 3000 feet deep and 18 miles across. North of Fernelius, and about halfway from it to Aliacensis, is another strange depression shaped like a flattened pentagon 39 by 47 miles across and 5200 feet deep, nonius may be the remnant of an extremely old crater since it appears to be intruded upon by the walls of large, ancient, Class 4 Walter on the northwest. The east wall of Walter is part of a conspicuous, bright, north-south scarp line about 100 miles long tangent to Nonius on the west.

South of the Heraclitus-Licetus complex, a distance equal to its length, we find Class 1 lilius, 38 by 42 miles across and 7900 feet deep. The bright crescent of the inner east wall shows well, and perhaps you can make out the bright central peak rising from the edge of the shadow that covers the west half of the crater. Tangent on the southeast is the

FIGURE SO. Numerous lava lakes and craters of many sizes, shapes, and ages crowd the upland west of Theophilus in this afternoon view. A tiny crater close to the left border west of Almanon has blanketed the area around it with bright ejecta. Note the chain of small craters running from the south wall of Abulfeda toward Catharina. It can be followed more than 100 milos, and it probably is due to volcanic action that produced a series of vents along a fault or crevasse. A shorter chain containing larger craters parallels it northwestward from a point under the label "Cyrillus." These and other linear features here mark the northwest-southeast lineaments of the grid system. (Compare with Figs. 49 and 51.) On April 21, 1972, Apollo 16 astronauts John Young and Charles Duke landed ®t a point slightly above the second L In Dollond. (120-'nch Reflector.)

FIGURE 51. Two battered old giant craters, Mauro-lycus and Stofler, stand out among their smaller neigh-bors in the rough country east of Tycho. Many ages are represented. Faraday E, for example, overlaps Faraday k, which overlaps Faraday, which overlaps the half crater beyond Faraday's northwest wall, which overlaps Stofler. The strange Licetus-Heraclitus com-P'ex, with its shallow connecting double valley, may be explained by a combination of collapse and impact events. Here again the northeast—southwest lineament Pattern is prominent. (Compare with Figs. 49 and 50.) ^20-inch Reflector.)

younger, sharper Class 1 lilius a, 23 by 26 miles across and 6200 feet deep. It appears as a dark speck since it is about half bright and half black. Continuing this line of tangent craters in the same direction is weaker Class 2 jacobi, 43 miles across and 12.500 feet deep. In walls and outline it resembles Lilius, but it has no central peak. Instead, it exhibits through a telescope six floor craters from three to five miles across, all of which are hidden tonight by the shadow that covers most of the enclosure. South of Lilius, a distance about equal to that between it and Jacobi, stands the half-illumi-nated Class 2 mountain-walled plain zach, 44 miles in diameter and 11,800 feet deep. According to Wil-kins and Moore: "Zach in its general appearance bears some resemblance to the terrestrial crater-lakes of Coatepeque and Ilopango in Salvador, or to Haleakala in E. Mauri, and may have been formed by similar forces; it is evidently of volcanic origin."

South of Zach a giant step, nearly equal to the last one taken, brings us to larger Curtius, easily seen as a narrow ellipse half bright and half black. If the libration in latitude is positive and large, Curtius will be foreshortened almost to a line, and craters farther south will be difficult to identify. Just southwest of Curtius is larger Moretus, its fully-illu-minated interior marked off by sharp arcs of brilliance on the east and blackness on the west. Possibly you may resolve the central mountain which is brighter than the floor but which, as yet, casts only a short shadow. By tomorrow night it will attain greater contrast. Northeast of Curtius, as far as Moretus in the opposite direction, is smaller Class 1 pentland, 36 miles across and 10,200 feet deep. It is more prominent than its size would indicate because it forms a double crater with pentland a on the south. The latter is 25 miles across and 10.800 feet deep, and tonight both craters are about half bright and half black. South of Pentland, and forming an equilateral triangle with it and Curtius, we may see near the terminator a small irregular black oval trimmed in light. It is Class 1 simpelius,. 43 by 54 miles across and 10,800 feet deep. It appears to be overlapped on the northwest by smaller but sharper and more regular simpelius e, 30 by 33 miles across and 12.800 feet deep. We now have reached latitude 73 degrees south, and the craters beyond arc both narrow and closely packed. The moon's south pole, of course, lies south of everything in view, "lunigraphically" speaking, but for our purpose of location it is due south of Moretus and Curtius. It is very close to if not beyond the limb.

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