Twentyday Moon

"Some are born great, some achieve greatness, and some have greatness thrust upon em," read Mal-volio from the mysterious letter in the second act of Twelfth Night. If we substitute "prominence" for "greatness" we could apply that famous declaration to the lunar surface features. In the first group are craters and mountains which are outstanding objects from sunrise to sunset two weeks later. Most of the objects we have been observing, however, be. long to the second class. Their "finest hour" lastj from a few hours near the terminator to several days, depending upon the size and construction of the feature. The last category consists of a steadily growing number of X's on lunar navigation charts~ X's that mark areas of no particular interest until space probes crashed or landed gently upon them and spots selected as touchdown targets for Apollo landings.

Craters such as Aristarchus, Copernicus, Gri-maldi, Plato, and Tycho are outstanding objects night after night, and they should be noted and enjoyed by the student of the moon even when not specifically called to his attention. In the case of Tycho, you probably have noted that the great ray system has been fading the last few nights. Soon it will be gone.

Due east of Tycho, a little more than halfway to the terminator, the great crater Maurolycus has risen again to prominence, its brilliant east wall and black west wall giving it an arresting appearance tonight. Tangent to Maurolycus on the southeast, Barocius also shows well. In the northern hemisphere the vast arc of the Apennines and Caucasus leads to the conspicuous crater pair Eudoxus and Aristotle. Close to the terminator, between the remnants of two maria, the magnificent trio Theophilus, Cyrillus, and Catharina contends strongly for our recognition. These are the outstanding features of the 20-day moon, but they are by no means all that should claim one's attention tonight.

In the dim zone between Theophilus and the terminator you may be able to spot smaller Madler as a tiny light circle before darkness overtakes its crest. Two Theophilus widths north of Madler, pear-shaped torricelli makes a little better showing. That odd enclosure, 6900 feet deep, is the union of two craters, the east one being 12 miles in diameter and the west one about half as large. East of Torricelli the terminator coincides with one edge of the great square peninsula (200 miles on a side) that is bounded by Maria Fecunditatis, Tranquillitatis, and Nectaris. The sun has set on all of it except for a few peaks to the north which shine like stars out of the blackness of the dark side.

The main body of Mare Tranquillitatis is bisected by the terminator, and the low-angle illuminatw® brings out some of its smaller markings. At the terminator and north of Torricelli, a distance equal to that of Theophilus to the south, you might be able» resolve irregular little maskelyne, which measure 15 miles across and 8200 feet deep. Near the shore line, midway between Theophilus and bright Menelaus in the Haemus Mountains, may be seen the tangent rings of sabine and ritter (Fig. 10). Both are Class 5, irregular, and about 18 miles across. Sabine on the southeast is 4600 feet deep while Ritter is 4300 feet deep. They are fully lighted by the sun, and their lava-stained floors are framed by delicate rings—light on the east and dark on the west. Far brighter than either is much smaller Dionysius northwest of Ritter about twice the separation of the latter from Sabine. While in the neighborhood don't miss prominent Delambre about one Theophilus length southwest of Ritter and south of Dionysius.

On the dark plain northeast of Ritter, a distance equal to that of Delambre in the opposite direction, you may find the bright inner east wall of smaller but brighter Class 1 araco, 16 miles across and 5900 feet deep. Between Arago and Ritter you might be able to see smaller Class 1 manners, 10 miles across, 5900 feet deep, and a difficult test (Fig. 10). North of Arago, a distance equal to that of Sabine in the opposite direction, is similar Class 1 ross, 17 miles across and 5900 feet deep (Fig. 10). Have a try at much fainter, smaller, shallower, polygonal maclear, 13 miles in diameter and 2300 feet deep, just southwest of Ross (Fig. 10). Northeast of Ross one Theophilus length, and just off the Archerusia Promontory, larger, brighter Pliny stands out prominently, about y3 bright and % black.

On western Mare Tranquillitatis are three of those unmarked but important spots that have had "greatness thrust upon em." Midway between Pliny and Dionysius unresponsive Ranger 6 crashed on February 2, 1964—a splendid shot up until the time it was supposed to send back pictures. One year and 18 days later perfect Ranger 8, its mission accomplished, struck the surface south of Pliny and east of Dionysius at a point which marks an equilateral triangle with Arago and Sabine. The plain east of Sabine, scouted by both Ranger 8 and Surveyor 5, was the touchdown area for Apollo 11 (3V2 crater diameters from Sabine), as we have seen.

The terminator coincides with the east shore of Mare Serenitatis, and tonight is an excellent time to look for the Serpentine Ridge that wriggles across it from Pliny north to Posidonius. There may be just enough light on its west slope and shadow to the east to bring it out for us. Look for a faint, light, wavy, discontinuous line, stronger toward the north e"d. Posidonius at the terminator is conspicuous as a bright ring with a mottled gray floor. Just south of on the rugged shore, a bright arc on the east edge of a black spot marks the location of Class 5 lemon-nier, 36 miles in diameter and 7300 feet deep on the east (Fig. 11). Its west wall has been reduced to a ridge only a few hundred feet high. The floor is hidden in shadow tonight, but when illuminated it is found to be unusually smooth and free of detail. From the west end of Lemonnier's wall the brightest portion of another ridge extends south some 80 miles parallel to the shore line and to the Serpentine Ridge.

Near the terminator east of Eudoxus is a small, irregular bright spot which is the sunlit massive east wall of plana, 26 by 31 miles across and 6700 feet deep. The mountain mass that forms the east wall is higher than the rest of the wall, and it separates Plana from old Class 5 mason on the east. The latter, 20 by 25 miles across and 6300 feet deep, is on the terminator and a very dim object if visible at all. Just north of Plana on smooth Lacus Mortis we find the much deeper but no larger Burg, all black except for a bright east crest and a light outer west wall.

North of Aristotle, about halfway to the terminator, the young crater oalle, 15 miles in diameter and 6600 feet deep, may be seen as a bright speck 011 the Mare Frigoris plain (Fig. 8). At the terminator north of Galle you may be able to resolve the narrow elliptical ring of ancient kane, 34 miles in diameter and 4300 feet deep, the light, broken walls of which appear continuous tonight but show large southern gaps under higher sun. One Plato length northwest of Kane look at the terminator for similar neison, 31 by 35 miles across and 7900 feet deep. Nearly tangent to Neison on the northwest is huge, shamrock-shaped meton, 110 miles across and 8200 feet deep. It is the union of three or four major craters, but the vast floor shows little if any trace of overlapping walls. Recently the name has been restricted to the northern crater of the group. The only strong markings on the floor are several light wall-to-wail streaks that cross from east to west. They are \ isible through small telescopes around full moon and are part of the splash pattern of the ray crater Anaxagoras 150 miles west. Even if the present floor resulted from a lava flow, as it probably did, its uniformity is most unusual. In a line west of Meton lie the three craters Barrow, Goldschmidt, and smaller Anaxagoras. The first two are washed out bright with only traces of wall shadows except for the strong mountain ridge between them, but the younger Anaxagoras shows well.

Let us now return to the southern hemisphere. Two Theophilus widths west of that crater much

PIGURE 48. The Altai Scarp cuts through rugged territory bordering Mare Nectaris, the southwest edge 01 which is shown beyond Beaumont and Fracastorius. The prominent irregular cliff, which rises 2 miles high 1,1 Places and curves northward some 600 miles, is Port of a vast ring concentric with circular Mare Neck's. Baldwin has traced it completely except where it ,s buried under the lavas of other maria. He believes th«t the shock wave resulting from tho impact which •xcavated the Nectaris basin caused the surface to ^ ck|e, break and drop away along the scarp. See Fig. f0r more of the cliff. (120-inch Reflector.)

smaller Kant stands out in its mountainous surroundings. It is still Vz bright, but its shadow and those of its neighbors are growing long. Southwest of Cyrillus, northwest of Catharina, and marking out an almost equilateral triangle with the two, is weaker, irregular, Class 1 tacitus, 28 by 30 miles across and 9300 feet deep (Fig. 5). Two Theophilus widths south of Tacitus is similar but older and even weaker Class 2 fermat, 24 miles across and 7400 feet deep (Fig. 48). Just east of Fermat a conspicuous, black, somewhat irregular line catches the eye. It comes south from a point near Tacitus, turns sharply to the southeast near Fermat, and continues on to the terminator. That is the Altai Scarp which was prominent as a bright line on the five-day moon.

South of Catharina and halfway to the Altai Scarp may be seen the small black ellipse, bright bordered on the east, of irregular polybius, 25 miles across and 7700 feet deep (Fig. 48). Two Theophilus lengths south of Polybius, beyond the Altai Scarp, the similar but younger Class 1 rothmann, 26 by 28 miles across and 9900 feet deep, stands near the terminator (Fig. 48). More than half its interior is black, but what is illuminated shines brightly. One Theophilus width southwest of Rothmann a bright crescent stands out. It is the inner east wall of larger Lindenau. The rest of the crater is lost in black shadow, partly its own and partly that of its larger, higher neighbor tangent on the west. That neighbor is Zagut, which shows well tonight and resembles the head of a bird with a stubby beak. The beak is the intruder on the east, Zagut E, which gives the crater a pointed outline on that side. The eye is a difficult young floor crater eight miles in diameter not far from the center of Zagut.

Tangent to Zagut on the south is a similar enclosure in both size and shape. It, too, is pointed on the east where the "beak" section is marked by a confusion of at least 10 small craters. Instead of one eye it has five. That crater, Rabbi Levi, wasn't just hit; it was sprayed. Immediately southeast of the wreckage of Rabbi Levi you may notice a black crescent. That is the inner west wall and just about all that is left intact of ancient, irregular riccius, 45 miles across, 5900 feet deep, and heavily damaged. Two Theophilus widths south of Rabbi Levi is the smaller and much younger crater nicolai, 24 by 28 miles across and 7000 feet deep (Fig. 49). With dark interior and bright east wall, it is the strongest of the numerous pits that are scattered throughout the area. An equal distance south of Nicolai, at the terminator, look for Pitiscus, a large black oval with bright borders on both east and west. Its greater neighbor on the south, Hommel, is enveloped in darkness with the exception of its bright outer west wall and a few high spots along other parts of the wall.

West of Pitiscus and south of Barocius our armless snow man shows well again tonight, but upside down without an inverting telescope. His torso is the largest crater, Bacon. His head is Bacon A, and his legs are Breislak on the east and Bacon B on the west.

Continuing south along the terminator, we may find three more large craters before we reach the limb near the south pole. Southwest of Pitiscus, about twice the combined widths of Pitiscus and Hommel, is the light-outlined black ellipse of Mutus. Just beyond Mutus is larger and more conspicuous Manzinus. Its broad inner east wall is illuminated completely and shining brightly, and its outer west wall also is strong. Beyond Manzinus, after an interval equal to its length, we come to somewhat smaller Class 1 schombercer, 53 by 56 miles across and 11.200 feet deep. If you don't find the last two or three craters don't be concerned about it. Under average conditions, the last three craters are each approximately tangent to the terminator, but the li-bration in latitude can introduce conspicuous variations in their positions not only with respect to the limb but with respect to the terminator as well at this phase.

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