The MOON : Part 4

Description of the Moon in Telescopes


The Moon to the telescopist is simply wonderful regardless of the size of the telescope employed, which is made even more interesting by the continuous monthly changes of the lunar phases. The best place to view the Moon is along the terminator. Along this line on the Moon is the sunrise or sunset during the lunar month, being the intense sunlight unimpeded by any atmosphere. Here the projected shadows are sharp and crisp on the lunar terrain,offering contrast between the inky black within the darkness and the brilliant whiteness exposed to the Sun. When the many mountains, crater walls, rocks and crevices cast long shadows across the flatter terrain, the outlines of the features are greatly extended, allowing the observer to see the represented topography as if you were standing on the lunar surface.

Each subsequent day finds the terminator move an obvious significant amount each day This portrays new features as the terminator moves east to west, increases the phase after new moon, or recedes west to east after full moon.

The following is a brief description of the features that an observer can see during on the brightened side of the Moon to the terminator. Further study can be made using a more detailed lunar map that shows many more features, whose fascination ca last almost a human lifetime.

NOTE : All lunar features and craters are expressed in metric units, either in metres (m.) or kilometres (km.).

Lunar Features Named

Aspects of the Moon During the Lunar Month

Map 1 - Features of the Moon (2.85 days)

The narrow crescent of the Moon, illuminated by the Sun, presents few objects of interest to the observer. The Mare Crisium or Sea of Crises or Conflicts, at it is called, is the most prominent object visible at this time. It measures 560 kilometres from north to south, 450 kilometres east to west. Note Promontorium Agaum, meaning Cape Agaum, 3,300 metres high jutting out of into the Mare at the south west, and the two small craters on the surface of the sea floor, a little east of centre. The southern one is Picard, the northern one Pierce.

North of the Mare Crisium is the crater Cleomedes, some 129 km. across. One walled peak is 3 kilometres high, and has a central mountain divided by three clefts. On the eastern wall is the very deep crater named Tralles. If the atmospheric conditions are favourable, a certain amount of detail can be seen on the dark or earth-lit portion of the Moon. The brilliant crater Aristarchus, and the darkest crater Grimaldi, on the eastern limb, have been seen.

Map 2 - Features of the Moon (3.87 days)

Petavius is one of the finest craters we can view on the Moon, whose rim extends 160 kilometres from north to south. Within its walled depths is divided with many valleys while with the central vast plain rises one single mountain 1,700 metres in height. A straight line radiates from this mountain extending southeast to the wall of the crater. This line, which in reality one great cleft, can be seen in 7.5cm telescope, and is best viewed a day or two after the Full Moon, when the Sun is setting upon it. In formation these clefts or rills are analogous to the American Grand Canyon. Petavius is especially noteworthy because of its convexity of its floor, the centre of which is 240 metre higher than the edges.

Langrenus is 145 km. in diameter. It contains a mountain peak 1,800 metres high. Note three small craters northeast of Langrenus forming a triangle.

Vendelinus is pear shaped and therefore easily identified. Note a small but brilliant crater on the northeastern slope of Furnerius. Burckhardth is the name of the crater just north of Cleomedes. North of it is Geminus, 87 km. in diameter. Its western wall rises to 5,000 metres in height. Gauss from north to south measures 177 km.

Map 3 - Features of the Moon (5.54 days)

The diamond shaped Sea of Fecundity and the Sea of Nectar, pentagonal in shape, are now visible. At the south of the latter sea note Frascatorius with it northern wall broken down. Endymion, near the western limb is the elliptical in appearance. Its western wall in places is 4 500 metres high. View Eudymion 3 days and 7 hours after New Moon and 2 days 9 hours after Full Moon.

Northwest of Fabricius and Metius is a deep cleft. On the top of the southern horn of the Moon are the peaks of the Leibnitz Mountains maybe seen.

Messier, 15 kms, across, and Messier A, are noteworthy. Two slightly diverging streaks run east from the latter for a long distance. Their character is still an enigma. Alleged chambers have been made in the shape of these craters.

East of Proclus is a peculiar yellowish brown patch somewhat diamond shaped. It is called Palus Solnii or Marsh of a Dream”. Hercules and Atlas are best viewed five or six days later after New Moon, or 3½ days after Full Moon. The former contains a crater pit and is 74 km. across. In the crater Atlas, which is 89 km. across, t he centre rises a central mountain.

Map 4 - Features of the Moon (6.74 days)

Note the crooked line of the Altai Mountains and the Taurus and Hæmus ranges, with Pliny, 51 kilometres across, between them. Dawes lies just west of Pliny. Just east of the Sea of Nectar is a striking group, Theophilus, Cyrillus and Catherina. The former is 104 km. across. Its walls in places is 5,500 metres high. Its central peak can be seen beyond the terminator five days after New Moon. Cyrillius is trapezoid in form and contains two peaks. The northwest portion of its wall has been demolished to make way for the wall of Theophilus. Posidonius on the western shore of the Sea of Serenity is 100 km. across and contains a crater. Its interior floor lies about 600 metres below the outer surface of the Moon. It is best viewed about six days after New Moon. North of Posidonius is a V-shaped bay called Lacus Somniorum or Lake of the Sleepers”. A peculiar ridge winds its way from Posidonius to Pliny. Across the Sea of Serenity and south of Posidonius is Le Monnier with its eastern wall broken down. Mount Argæus, north of Pliny, 2 500 metres high, is a fine site when the Moon is five days old. North of the Sea of Nectar note Isadore and Capella, with a peak over 4 km. high between them. The ring of Capella is cut down by a broad cleft.

Northeast of Mare Crisium note Vitruvius, Maraldi, Littrow and Röemer. South of Fabricius and Metius are three small craters close together, Pitiscus, Hommel and Viacq. Steinheil, northwest of them, is shaped like a figure 8”. Polybius and Pons lie on opposite sides of the Altai Mountains.

Map 5 - Features of the Moon (7.75 days)

In the south Maurolycus 240 kilometres across and Stöfler are conspicuous. The former is best viewed about the time of the Moons first quarter. At Full Moon it is practically invisible. Some of the peaks are 4,600 metres high.

About the centre of the Moon, just west of the terminator, lies Albategius, 103 km. across, and north of it Hipparchus, 145 km. in diameter. The latter exhibits signs of demolition and is presumably older than Albategnius, which is very deep and it comparatively perfect.

Note Menelays and Suipicius Gallus on the south side of the Sea of Serenity with Manilius between them. It is not known why these and a few other crater are so conspicuously bright.

The Caucasus Mountains are prominent in the south of Eudoxus and Aristoteles. In the centre of the range is Callipus. The dotted line across the Sea of Serenity represents a light streak radiating from Tycho, 3 200 kilometres to the southward. It crosses Bessel, 23 km. in diameter, situated in the Sea of Serenity. The character of these light streaks is unknown. The small triangular shaped crater east of the Caucasus Mountains is Theætetus, interesting because a French observer claims to have seen smoke rising from it!

The Sea of Serenity is 690 km. long, and about as wide. Its area is 480 000 km2. Godin, 37 kilometres and Agrippa 44 km. in diameter, respectively, are fine objects when seen on the terminator. A minute point of light is alleged to be seen near them. Southeast of Piccolomini are three craters forming a triangle. Zagut is the largest.

Map 6 - Features of the Moon (9.22 days)

Clavius is conspicuous in the south. It is 225 kilometres across, 50 800 kms2 in area, an a peak on its western wall is 4,400 metres high. Within its walls ninety craters have been counted.

Tycho, 87 km. in diameter, is the perfectly formed crater north of Clavius. A system of light streaks extending over one quarter of the visible hemisphere radiating from it. North of Tycho, just west of the terminator lie two groups, containing three crater each. The largest in each group lies to the north.

The Apennine Mountain, a grand range, start from Mt. Hadley, 4,600 metres high, and terminate at Eratosthenes, 730 km. to the southeast. Eratosthenes, 61 km. across, is 2,400 metres deep. It contains three conspicuous central peaks.

Archimedes 80km., Autolycus 37km. and Aristillus 55km. in diameter, respectively, lie north of the Apennines. Cassini to the north of them, contains two central pits. More than fifty objects have been detected within the walls of Archemides. Note the small peak Linné north of Mt. Hadley. Alleged changes have been noted in it form.

The Alps are pierced by a great cleft, 129 km. long, and from 5.6 km. and 10.5 km. in width. Its depth is at least 3,500 metres. Ariadæus is connected with Huginus by a valley best observed at First Quarter, being situated on the western shore of Mare Vaporum or Sea of Mists”. Note the Sinus Æstuum or Gulf of Hearts” south of Mare Vaporum.

Map 7 - Features of the Moon (11.78 days)

Note that Cichus, north of Tycho, has a crater on the eastern wall only 10 km. across.

West of Birt note the Lunar Railway or Straight Wall, a cliff line 105 km. long and 300m. high, terminating in the Stag Horn Mountains, best viewed one or two days after the First Quarter. The western shore of Mare Nubium or Sea of Clouds” outlines the profile of the Old Lady of the Moon”. Her hooked nose is just southeast of Ptolemy. Make sure to see Bullialdus, 45 km. across and 2,700 metres deep, along with Gassendi, some 56 km. in diameter. There are many curious clefts in the walls of Gassendi. North of it is Letronne, its north wall broken down.

Copernicus is conspicuous. It contains eight central peaks, and one is 730m. high. Its walls are terraced on the inside, and it is the centre of a rayed system.

Plato, 97 km. across, is one of the darkest spots on the Moon. The German astronomer Johannes Hevelius called it the great black lake”. South of it note Pico, some 2,400 metres high. Capes or Promontoriums Heraclides and La Place are at the extremities, respectively, of the Sidus Iridium, or Bay of Rainbows”. They are 218 km. apart at each end of the Jura Mountains. The former is 1,200 metres high and its shadow forms the silhouette for the Moon Maiden”, best viewed when the Moon is a eleven days old.

The Carpathian Mountains, north of Copernicus, are best viewed ten days after New Moon. East of them is Tobias Mayer, 32 km. across and 2 900 metres deep. Kepler, 2,900 metres deep and 35 km. across, is notably bright. Newton, south of Clavius, is 229 km. long and 7,300 metres deep, the deepest crater on the Moon. Note the circular Mare Humorum or Sea of Humors”, the darkest of the Seas.

Map 8 - Features of the Moon (14.4 days)

The telescopic view of the Full Moon, contrary to popular notion, is disappointing. The brilliancy of the reflected dazzles the eye, eliminates the shadows of the great peaks and renders the interesting details visible.

Grimaldi on the eastern limb, 240 km. long by 208 km. broad, is the darkest spot on the Moon. Northwest of it is Oceanus Procellarum, or Ocean of Tempests” is Aristarchus, the brightest spot on the Moonand is 45 km. across. It is and connected to 39 km. Herodotus by a short dark ray. A winding valley starts from it and can be seen traced across the sea for the long distance of 160 km.

Note the patches west of Copernicus, the colour of Palis Somnii, the brilliant craters Proclus, Ariadæus, Menelaus, Manilius, Sculpicius Gallus and Aristarchus, and the black craters Plato and Gramaldi. Observe the Riphæ Mountains, north of Mare Humorum, and the Harbinger Mountains north of Aristarchus. The dark patch north of Mare Imbrium extending from the Caucasus Mountains to Oceanus Procellarum is Mare Frigoris or Sea of Cold”. The bay that seems to connect the Mare Frigoris with Ocean Procellarum , north of the Bay of Rainbows is Sinus Roris or Gulf of Dews”. Archimedes, Autolycus and Aristillus are surrounded by an area of lighter hue than Mare Imbrium. This region is called Palus Putredinus or Marsh of Corruption”.

The ray systems emanating from Tycho and some other systems are more prominent at Full Moon than at other times. All the southern and western portions of the Moon are wanting detail owing to the intensity of light.

Last Update : 10th October 2012

Southern Astronomical Delights © (2012)

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