Updated:  1 February 2025

 


In 2016 a new section
"Lunar Feature of the Month" was added to "The Sky Tonight" webpage.

The features chosen are craters, mountain ranges, peaks, volcanoes, rilles, grabens, fault scarps or other objects on the Moon, selected at random, which have unique or spectacular attributes.

Each object is illustrated with a recent photograph taken with Starfield Observatory's Alluna RC20 telescope, located in Queensland, Australia. If a better picture is obtained at a later date, it will replace or supplement the original one. The high-resolution bitmap images are compressed into jpeg format to make the files about one seventh as large, and therefore more suitable for webpage use.

As all large lunar features are named, the origin of the name will be given if it is important
.

______________________________________

This page is an Archive of the Second Series of lunar features described from  # 101 in January 2025 to last month.  Earlier images in the First Series ( # 1 - # 100  ) are available  here .

To help the lunar observer to find these features, each set of ten is preceded by an image of the Full Moon on which the locations of the ten photographs immediately following are shown according to their numbers in this series.
 


Finding your way around the Moon:            1  -   Seas and an Ocean


 

From north to south:


Latin Name
 

 English Equivalent

Mare Humboldtianum

Mare Frigoris

Mare Imbrium

Mare Serenitatis

Oceanus Procellarum

Mare Vaporum

Mare Crisium

Mare Marginis

Mare Insularum

Mare Tranquillitatis

Mare Smythii

Mare Fecunditatis

Mare Cognitum

Mare Nectaris

Mare Nubium

Mare Humorum

 

Humboldt's Sea

Sea of Cold

Sea of Rains

Sea of Serenity

Ocean of Storms

Sea of Vapours

Sea of Crises

Sea at the margin

Sea of Islands

Sea of Tranquility

Smith's Sea

Sea of Fertility

Sea that is Known

Sea of Nectar

Sea of Clouds

Sea of Moisture
 

(All of these are dry lava plains, and nine are basins. The names of most of them date from 1651.)

 

Finding your way around the Moon:            2  -   Mountain Ranges


 

In alphabetical order:  


   Latin Name
 
English Equivalent
 

Montes Agricola

Montes Alpes

Montes Apenninus

Montes Archimedes

Montes Carpatus

Montes Caucasus

Montes Cordillera

Montes Haemus

Montes Harbinger

Montes Jura

 Montes Pyrenaeus

Montes Recti

Montes Riphaeus

Inner Montes Rook

Outer Montes Rook

Montes Secchi

Montes Spitzbergen

Montes Taurus

Montes Teneriffe

 



Agricola Range

Alps

Apennines

Archimedes Mountains

Carpathian Range

Caucasus Mountains

Cordillera Mountains

Balkan Mountains

Harbinger Mountains

Jura Mountains

Pyrenees

Straight Range

Ural Mountains

Inner Rook Mountains

Outer Rook Mountains

Secchi Mountains

Spitzbergen Mountains

Taurus Mountains

Teneriffe Mountains

 


 

Finding your way around the Moon:            3  -   Craters, Mountains and Valleys

The numbers on this lunar chart refer to the photographs listed in the table which follows:
 

 


No.
 
 Lunar feature No. Lunar feature No. Lunar feature

101

 

 

Mouchez + Pascal + Sylvester + Philolaus + Carpenter


 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

Observing the Moon
 


Terrae and Maria

When observing the Full Moon with the unaided eye, the first thing one notices is that it appears white with some darker patches. Ancient people thought that the Moon was a mirror reflecting the continents and oceans of the Earth, but they never agreed on whether the dark patches were the lands or the seas. In the 1590s, the Englishman William Gilbert made the first drawing of the Moon showing features we can vaguely recognise, but he named the dark patches as lands, and the lighter ones as seas. On his naked-eye drawing, a dark oval patch was named the "island" of Brittannia (sic). Sixty years later Giovanni Riccioli named it as a "sea", the Mare Crisium or Sea of Crises. By Riccioli's time primitive telescopes had revealed that the light areas were the lands or "Terrae",  and the dark areas were seas or "Maria" - it took many more years before the "seas" were found to be dry plains of solidified lava, and there was no liquid water on the Moon.

The Earth is 4.57 billion years old. The Moon is slightly younger, 4.425 billion. The Moon appears to have formed around the time the Earth's core was becoming solid and stable. Between 4.1 and 3.8 billion years ago, a high number of asteroids or minor planets left over from the formation of the Solar System were attracted by gravity into collisions with all the larger objects in the Solar System. The evidence of these impacts remains visible on all the terrestrial type planets and moons, but not the gas and ice giants whose surfaces we cannot see. The atmospheres on the Earth, Venus, and to a lesser extent Mars burned up all but the largest of these impactors. This cataclysmic event is known as the Late Heavy Bombardment or LHB.

The maria on the Moon were formed by collisions with asteroids or minor planets during the LHB. These impacts created large basins in the lunar crust which promptly filled with molten magma, which spread out onto the surface as lava flows, the basaltic nature of the magma causing the dark grey colour. Probably the first of these impacts created Mare Anguis, Mare Australe, Mare Fecunditatis, Mare Frigoris, Mare Insularum, Mare Marginis, Mare Nubium, Mare Smythii, Mare Spumans, Mare Tranquillitatis, Mare Undarum and Mare Vaporum (earlier than 3.92 billion years ago). After that, the Mare Crisium, Mare Humboldtianum, Mare Humorum, Mare Nectaris and Mare Serenitatis (3.92 to 3.85 billion years ago) were formed, then Mare Imbrium (3.85 to 3.8 billion years ago), and finally Mare Cognitum, Mare Orientale and Oceanum Procellarum (3.85 to 3.2 billion years ago).


Lakes, Marshes, Bays and Promontories

There are numerous smaller areas on the Moon that exhibit dark lava flows from strikes by less massive impactors. These are named as Lakes (there are 17, one example is the Lacus Mortis - Lake of Death), or Marshes (there are 6, one is Palus Epidemiarum - Marsh of Epidemics). There are 11 bays on the Moon, each being on the edge of a mare. They have names beginning with "Sinus", and the most spectacular is the Sinus Iridum (Bay of Rainbows). This feature has a promontory at each end of the "bay", the western one being "Promontorium Heraclides" and the eastern one "Promontorium Laplace". There are seven other Promontories on the Moon.


Mountains, Ranges, Valleys and Slopes

There are hundreds of mountain peaks on the Moon, many within craters, many as peaks in crater rims or mountain ranges, but only a few as isolated peaks protruding above flat lava plains. Two of the latter type are Mons Pico (2.4 kilometres high) and Mons Piton (2.25 kilometres high), which stand proudly isolated in the Mare Imbrium.

There are 18 mountain ranges, and 11 of them are around the margins of the maria, forming the circumferential boundaries of the basins created by the LHB impacts. For example, the impact that created the Mare Imbrium (Sea of Rains) threw up seven mountain ranges around its perimeter. These, starting from the north-west and moving clockwise, are the Montes Jura, Montes Recti, Montes Teneriffe, Montes Alpes, Montes Caucasus, Montes Apenninus, and Montes Carpatus. Some ranges are related to pyroclastic activity, such as the Montes Agricola, Montes Archimedes and possibly Montes Harbinger.

The Moon has some valleys, too, cutting through mountainous areas. There are eleven all told, but the most famous are the Vallis Rheita in the southern hemisphere, and the Vallis Alpes (Alpine Valley) and Vallis Schröterii (Schröter's Valley) in the northern. The latter two valleys are remarkable in that they both have a very fine sinuous rille running for almost their entire length, which is very challenging to detect.

There are some single fault scarps on the Moon, which cross flat plains like a gently sloping cliff 100 kilometres long or more. The two most notable are the Rupes Recta or Straight Wall (110 kilometres long), which crosses the Mare Nubium and is 300 metres high. Another is the Rupes Liebig (180 kilometres long), which is on the western margin of the Mare Humorum. The appearance of both of these slopes varies dramatically, depending on whether the Sun is rising or setting (see item  # 13   in the  Lunar Feature of the Month Archive - First Series ). The longest scarp is the Rupes Altai, which has a length of 480 kilometres, but is broken in places.

Rilles

The word 'rille' is German for 'groove'. These come in two types and are called Rima or Rimae (plural). One type is a V-shaped valley which can be straight or sinuous. Some are extremely long and begin at a small crater. They could possibly be collapsed lava tubes. There are many fine examples such as the Rima Marius, Rima Hyginus, Rima Hadley, Rimae Triesnecker and Rimae Prinz. The second type has two fault scarps two or three kilometres apart, running parallel often for hundreds of kilometres. Between them, the land has dropped down for a kilometre or so, leaving a flat floor between the scarps. On the Earth, similar features are known as grabens or rift valleys. Fine examples include the Rima Hesiodus, Rima Cauchy, Rimae Goclenius and Rimae Hypatia.


Volcanoes and Domes

Although no current volcanic activity has ever been observed on the Moon, there is widespread evidence that there has been considerable activity in the past. There are numerous shield volcanoes visible either singly, e.g. Kies Pi, in clusters of half-a-dozen or so (the Hortensius group) or in larger groups. The major group is the Marius Hills of more than a hundred. Many appear as low domes of about 10 kilometres diameter, and heights of a few hundred metres. At the summit of many can be found a volcanic vent, sometimes two, or a deep caldera as with Mairan T. The largest single volcanic complex is Mons Rümker with 22 volcanic craters. In addition, many craters and clefts are associated with ash vents which stain the nearby moonscape with dark patches of ash. Some good examples are in the craters Atlas and Alphonsus. The largest area of volcanic activity is north of the crater Schrӧter, where about 9000 square kilometres of lunar territory have been covered with dark-coloured ash associated with eruptions and pyroclastic flows. It is one of the darkest parts of the lunar surface (see item  # 35   in the  Lunar Feature of the Month Archive - First Series ).

 
Other Features

The lava plains that formed the maria cooled while still exhibiting waves and ripples. These solidified, and now appear as Dorsa (singular form "Dorsum"), popularly known as "wrinkle ridges". They are found in all the maria, but are particularly notable in the Mare Serenitatis and the Mare Imbrium. 


Craters, craterlets and walled plains

The Moon is covered by small, round depressions due to bombardment by asteroids, meteors and comets which hit the surface at high speed (roughly 25 kilometres per second) and explode, as their kinetic energy is converted instantaneously into heat, vapourising the impactor and blasting out a bowl-shaped crater. It is estimated that there are 300 000 impact craters on the Moon's near side that are larger than one kilometre across. Of course there are billions of smaller ones, ranging in size down to a metre or less.

The largest impactors struck the Moon early in its history, more than 3.8 billion years ago. These caused the major features we see today, particularly the dark lava plains called "mare" ("seas"). Over the eons the number of these impacts has reduced to near zero, and since astronomers have been looking at the Moon through telescopes, no new craters have been detected. Yet, occasionally monitoring cameras pick up a flash of light on the dark side of the Moon, so there are occasional meteor strikes, but not large enough to leave a visible crater.

Many craters had been forming on the Moon since the beginning, especially prior to the LHB which created the maria. There is much evidence on the Moon of ancient craters being swamped by molten lava surging across the surface after an LHB strike, so that they are almost or completely covered. Their presence can still be faintly seen, and they are called "ghost craters". One example is Stadius. Often, the lava surged around an existing crater without penetrating it. Other times, the lava forced a breach in the crater wall and then swept in, flooding the interior. Good examples of this are Fracastorius, Letronne and Prinz.

Early selenographers such as Hevelius drew their maps showing the craters as hollow mountains, as they thought that they were volcanic calderas similar to those on Earth. Hevelius named them all as mountains, e.g. he named one feature "Mount Sinai", but Riccioli, realising that it was a cavity in the surface, named it "Tycho". Only a few people in the seventeenth century thought that these "cavities" might be caused by impacts from space, but Robert Hooke experimented by dropping lead balls into softened pipeclay and thought it might be true. At the time, no-one knew about objects flying through interplanetary space at random. The cavities were given their proper name "crater" (from the Latin word for "cup") in 1791 by Johann Hieronymous Schröter - he also gave us the word "rille" (German for "groove").

Craterlets have a diameter of less than 10 kilometres, and are generally bowl-shaped with a raised rim and a small ejecta blanket around the outside of the rim. Craters larger than this, but less than 150 kilometres across, often have a cluster of mountains in the centre. This is because the initial impact sends down a shock wave to the bedrock, which rebounds back up. It fractures and lifts the newly-formed crater floor, creating the mountains more or less in its centre. Huge amounts of melted rock are created by the impact, which cover the surface all around the new crater like a darker basaltic halo. Quite often, the initial blast sends rocks and boulders as big as flying mountains skittering across the lunar surface for hundreds (sometimes thousands) of kilometres, leaving great gouges in the moonscape. These are what cause the light-coloured so-called "rays" that are seen around craters such as Tycho, Copernicus and Kepler. Such craters often exhibit areas around their floors where the walls have slumped down in landslides, creating spectacular terraces.

It is often seen in such craters that the fissures in the newly fractured floor release the pressure on the superheated bedrock, which then becomes liquid and expands. It forces its way to the surface as molten magma, oozing out of the fissures and spreading out over the new bowl-shaped floor which becomes dark lava when it cools. Sometimes, only a small amount of lava emerges, as in the crater Copernicus; at other times it covers the entire crater floor, often completely swamping any mountains on the floor, as in the crater Plato, which Hevelius called "Lacus Niger" (Black Lake). If such flat-floored craters are larger than 80 kilometres in diameter, they are called "walled plains". Generally, the rising magma fills the new crater up to a level equal to the surrounding lunar surface or slightly lower or higher. One crater in which the upwelling lava filled it right up to the top of its raised rim and then overflowed down the outside slopes to create a level plain beyond, is Wargentin. It gives the appearance of a plateau or tableland. Large walled plains include Ptolemaeus, Alphonsus, Hipparchus, Endymion, Plato, Petavius, Posidonius, Grimaldi, Clavius and Humboldt.

Sometimes a flying mountain ejected from an impact will bounce across the surface, leaving a trail of secondary craters. These are called "Catena" (Latin for "chain"), and two of the best known are the Catena Davy and the Catena Abulfeda.
 

Basins

The largest crater on the near side of the Moon is Bailly (see item  #64   in the  Lunar Feature of the Month Archive - First Series ). Although it was a major impact early in the Moon's history and is 303 kilometres in diameter, its floor was not fractured and no mountains were thrust up. There are, though, a few low ridges. No lava emerged to level out its floor, and over the eons Bailly has been severely battered by thousands of impacts of various sizes, so that it has become described in Wikipedia as a "field of ruins". Bailly is regarded not so much as a very large crater, but as a small "basin". Most basins are much larger, and all are formed by huge impacts. There are 29 all told, and some of the largest are named as "Mare" (singular, "Maria" is the plural form). Nine of the Maria listed in the table above are basins.

 

NOTE:
 

In the above section, reference is made to many named lunar features. A majority of these are pictured in the following Archive, where they can be examined. To locate their numbers in the Archive, find their names in the Tables and Charts that have preceded this section. For example, you may wish to look at a picture of the crater known as Philolaus. Reference to the Table preceding this section will show that an image of Philolaus appears in item  # 101 .   Simply scroll down to  101  to see the image which includes that crater.

 

The waxing gibbous Moon at 9:25 pm on August 1, 2017.

 

The photograph above shows the Moon when approximately nine days after New, just after First Quarter. The cluster of two large craters with a large, circular walled plain shown in detail below can be found in the northern hemisphere, near the top left corner. It is close to the line between the sunlit area and darkness. This line is called the 'terminator' and it moves in a westerly direction across the moonscape at the latitude of the features shown below at a speed of 16 kilometres per hour.

 

This image was taken at 7:50 pm on July 2, 2017. 63% of the Moon was illuminated, 1.7 days after First Quarter.

 
 


The image above shows a spectacular area in the south-eastern end of the Mare Imbrium (the Sea of Rains). It is a dry lava plain containing wrinkle ridges (Dorsa); a large bowl-shaped impact crater called Autolycus, a larger bowl-shaped impact crater called Aristillus with a cluster of mountains in its centre; a walled plain called Archimedes with spectacular terraces around its inside walls; a ghost crater; a line of cliffs 85 kilometres long; ranges of mountains; isolated peaks and hills; clefts; rilles; a large pyroclastic area; dozens of tiny craterlets and, to top it off, the Apollo 15 landing site next to Mount Hadley, where David R. Scott and James B. Irwin were the seventh and eighth astronauts to walk on the Moon (they took a lunar rover with them so that they could ride to Hadley Rille).
 

 

This image was taken at 7:16 pm on August 1, 2017.  On the Moon, the Sun was slightly higher in the sky than in the previous images.  67% of the Moon was illuminated, two days after First Quarter.
 
 

A rotatable view of the Moon, with ability to zoom in close to the surface (including the far side), and giving detailed information on each feature, may be downloaded  here.  A professional version of this freeware with excellent pictures from the Lunar Reconnaissance Orbiter and the Chang orbiter (giving a resolution of 50 metres on the Moon's surface) and many other useful features is available on a DVD from the same website for 20 Euros (about AU $ 33) plus postage.
 

Above is a photographic animation from Wikipedia Commons showing the lunar phases. It also shows the Moon's wobble or libration, and how its apparent size changes as it moves from perigee to apogee each month. Such downloads are freeware, although the authors do accept donations if the user feels inclined to support their work.


Technical information :


The following pictures in this Archive were taken at Starfield Observatory, Nambour, Queensland, Australia through an Alluna Ritchey-Chrétien RC-20 reflecting telescope, built to order in Germany. The aperture is 508 mm and the focal length is 4080 mm. The focal ratio is therefore f/8.  Most images but not all were taken using a 2x Tele Vue Powermate to increase the image scale. The camera used is a ZWO ASI 290MM with a red filter. It is a video camera and captures a video stream from which the clearest frames are extracted and then stacked to produce the final image. The software used includes SharpCap 2.9, FireCapture V2.5, AutoStackkert! 3.1.4, RegiStax V6.1.08, Planetary Imaging Pre-processor (PIPP) V2.5.9, AstroSurface V3, and Adobe Photoshop V8.0.

We can work out the scale of the images in the Archive below by using the first picture in the  Lunar Feature of the Month Archive - First Series  ( #1 Clavius )  as an example:

The equatorial diameter of the Moon = 3476 kilometres. On the night the photograph of Clavius was taken, 2 August 2017, the Moon was at apogee (its monthly maximum distance from Earth, in this case 405 053 kilometres). Its angular diameter on the sky at that time was 29.5 arcminutes.

Clavius has a diameter of 225 kilometres, so its angular diameter on that occasion can be determined in proportion from that of the Moon:   3476 km : 225 km :: 29.5 arcminutes : x arcminutes   ( 3476 is to 225 as 29.5 is to  x ,  or  225 multiplied by 29.5 divided by 3476 equals  x arcminutes ).

Simple arithmetic gives the angular diameter of Clavius ('x arcminutes') on that night to be 1.91 arcminutes or 114.57 arcseconds. If the image is printed to fill an A4 sheet in landscape format, and examined from a normal viewing distance of 28 centimetres or 11 inches, the image of Clavius will subtend an angle of 64 degrees or 230 400 arcseconds at the eye. To find the magnification of the image at that distance, we can calculate by which number 114.57 arcseconds must be multiplied to arrive at an answer of 230 400 arcseconds.

230 400 divided by 114.57 equals 2011. Therefore, to examine an A4 reproduction of  #1 Clavius  at a normal reading distance is equivalent to viewing it through a telescope with a magnification of 2011 times ( magnification = 2011x ). Such a view is what one would see through a spacecraft window if orbiting the Moon at an altitude of 200 kilometres.  Those pictures requiring a larger field, such as maria or lengthy mountain ranges, have been taken with the 2x Powermate removed. Examples of this procedure are the two images of Mare Imbrium (  #12  ) and also one of the Montes Apenninus (  #15  ). This results in a field of view four times larger in area, but with a magnification of only 1005x, similar to orbiting the Moon at an altitude of 400 kilometres.

The techniques outlined above enable very fine details on the Moon and planets to be detected in the final images. That of  #1 Clavius  in the First Series of this Archive contains hundreds of sub-kilometre craterlets. Ten of them are indicated by yellow lines in the enlargement immediately below. Some are tinier than 750 metres diameter, which is approaching the minimum size detectable from Earth with an aperture of 500 mm under optimum seeing conditions.


 

Clavius  (central section).

 

 

 

 

Archive   -   Second Series

 

 

 

Generally speaking, most telescopic observers have their favourite lunar features, most of which have already appeared in the first hundred images in this Archive. Yet there are many more interesting features on the Moon that for one reason or another attract little attention. Whereas craters near the Moon's centre as seen from Earth appear as if from a spacecraft flying overhead looking vertically down, craters around the Moon's limb or 'edge' are seen in profile, which means that features in the craters' interiors such as rilles cannot be seen. Also, craters near the limb may be in the zone of libration, which means that they spend some time each month out of sight from Earth. Features on the near side of the Moon are visible for up to two weeks each month if they are not close to the limb, but features near the limb can only be easily seen if there is a favourable libration bringing them into view at a time when the lighting of the area permits them to be seen. Features near the limb are therefore much more difficult to observe. Those near the eastern limb can only be observed for a few days after New Moon, and a few days after Full Moon. Those near the western limb can only be observed for two or three days before Full Moon, and two or three days before New Moon, at dawn. Such observing sessions need to be coordinated with the Moon's libration using software such as the Virtual Moon Atlas.

In November and December in 2024 ( items  # 99  and  # 100 of the  Lunar Features of the Month Archive - First Series ), the heavily cratered area to the south-east of the Moon's North Pole was described, as it is an area that is close to the lunar limb and therefore greatly foreshortened and affected by libration. In the following months we will again begin at the North Pole, but this time we will travel south around the horizon to the Moon's equator, which is an area often overlooked by lunar observers. We will become acquainted with numerous craters and walled plains which are usually out of sight. Some can only be photographed within a few hours of Full Moon, when the features not near the limb have fewer or no shadows and so the pictures appear lacking in detail and contrast. To assist in recognising these features, they were photographed on 22 May 2024 and 23 May 2024, when libration was very favourable. Full Moon occurred at 11:54 pm on 23 May, 2 hours and 48 minutes after the last photograph. Occasional clouds interrupted the sequence three times - earlier photographs of these areas under almost identical conditions have been inserted into the sequence for the sake of continuity. This set of images began in January 2025 and will run until the following August.

Early observers of the Moon named some of these features, but they neglected many of those close to the limb. Later observers using better equipment added the names of modern scientists and philosophers. This is why we will meet in this sequence of images some well-known names such as Balboa, Vasco da Gama, Pascal, Dalton, Stokes, Langley, Galvani, Bunsen, Struve, Volta, Babbage and Lavoisier, and from the twentieth century Aston, Rontgen, Nernst, Lorentz, Einstein, Bohr, Eddington, Russell and Von Braun. The crater commemorating Wernher von Braun, the German-American rocket pioneer, was named by the International Astronomical Union (IAU) in 1994.

 

 


These two images of the North Pole area are from the 
Lunar Feature of the Month Archive - First Series  ( item   # 99  ), and are included here to assist in matching their lunar features with those shown in item  # 101  following:

 


The two images below are close-ups of the area around the lunar North Pole (shown with a blue asterisk).

 

This image was taken at 7:25 pm on 4 October July 2022.



 


 

The two new medium-field images immediately following are included here to assist in matching up the details in six images that appeared in item  # 99  in the  Lunar Feature of the Month Archive - First Series  with those above, and those that follow in item  # 101 below:
 


 

This image was taken at 9:27 pm on 31 July 2023. The angle of view is twice that of the previous pair above. The Sun was very high in the Moon's sky, causing the lighting to be flatter with much smaller shadows. Full Moon occurred 32 hours after this image was taken.






Note the light-coloured streaks radiating for hundreds of kilometres from the 51-kilometre crater Anaxagoras (centre). As most of these 'rays' are to the north-east, east and south-east of the crater, it is obvious that the incoming impactor was travelling at a low altitude from the west (left-hand) side.
 
 

 



Key to feature 101 below.
 


101:   January  2025


This month's feature is the rugged area adjoining the Moon's North Pole. It extends west to longitude 50º west and south to latitude 65º north. It includes an ancient walled plain called Mouchez, and a much more recent crater called Philolaus. This is the first in a sequence of 44 images to be presented this year, covering the zone of libration from the North Pole around the north-western limb of the Moon to the Equator. As the sequence progresses, the camera will start from the walled plain Hermite and then move west, following the Moon's north-western limb in a southerly direction until we reach the lunar equator in the vicinity of the crater Riccioli. Features recorded such as craters will move to the right as the sequence continues, as the image frame moves to the left. The average width of each image will be 265 kilometres.
 

This area adjoins that shown as image  # 99  in the  Lunar Features of the Month Archive - First Series.  This image was captured at 9:36 pm on 22 May 2024.

 




 

The eastern walls of the 110 kilometre diameter walled plain Hermite are only 50 kilometres from the Moon's North Pole itself.  Hermite is in the zone of libration, as is the nearby 58 kilometre walled plain Sylvester .  Both of these features are about 3.8 billion years old, or middle-aged as lunar features go.  South of these two, the lunar surface has been battered by eons of impacts, the walled plains Poncelet  (70 kilometres), Mouchez  (83 kilometres) and Anaximenes  (80 kilometres) showing considerable degradation. On the other hand, the crater-plain Philolaus (71 kilometres) is much more recent, its age being less than 1.1 billion years. The rim of Philolaus remains sharply defined. A small part of the floor has been flooded with lava, but the rest of the floor is very rugged, with numerous hills and four clusters of mountains. The interior crater walls show many land slips (particularly on the southern or near side), which now appear as terraces.
 

Philolaus

Philolaus of Croton (470-385 BCE), born in southern Italy, moved to Greece and learned of the theories of Empedocles. Becoming a follower of Pythagoras, he joined the Pythagoreans at Thebes, between Athens and Delphi. Like other Greek philosophers, he was devoted to perfection. The circle was the perfect plane figure, and the sphere the perfect solid figure. He believed that the number ‘10’ was perfect, as it was the sum of the first four integers (1 + 2 + 3 + 4). Therefore there should be 10 celestial bodies, but he could see only nine – the Sun, Moon, the Earth, the five naked-eye planets, and the sphere of fixed stars (counted as one item).

Aristotle tells us that this was the reason that Philolaus decided that there must be a tenth planet, which he called the Antichthon or ‘counter-Earth’. He set all of these bodies, including the Sun, in orbit around Hestia, the central fire of Pythagoras, which people could never see because the side of the Earth on which they lived was always facing away from it. He went on to say that the counter-Earth was also never seen, because it was on the opposite side of the central fire from the Earth, and so was always hidden from view. This erroneous cosmology was based more on philosophical principles and wishful thinking than on real astronomical observations, but it had one remarkable feature. For the first time in history, it  described the Earth as one of a family of two planets moving in circular orbits, though not around the Sun, but around Hestia, the central fire. It was the first suggestion of a planetary system revolving around a central body, with its various components also rotating upon their axes. Two thousand years later, Nicolaus Copernicus would analyse the ideas of Philolaus when developing his own truer conceptions.


This area adjoins the left-hand (western) side of the pair above.  This image was captured at 9:46 pm on 22 May 2024.



 

In this image, the craters Poncelet and Philolaus are now on the right-hand side, and Anaximenes is in the centre.  The walled plains Pascal (106 kilometres) and Poncelet C (67 kilometres) have now come into view, as has the more recent crater Carpenter (40 kilometres).  A small craterlet called Anaximander H (9 kilometres) can be found near the lower left-hand corner.  A huge walled plain called Brianchon (146 kilometres), which lies in the zone of libration, appears in this image as a dark void, but when it is illuminated one day later (see next image), the far ramparts of Brianchon are revealed, and the summits of small hills in the centre of the floor catch the light of lunar dawn.

Pascal

Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor and philosopher. He was also a contemporary of René Descartes. In 1642 aged not yet 19, he built mechanical calculators that could add and subtract. Eight of his "Pascalines" still exist in museums today.

 

This area shares many features with the four images above. This one was captured at 8:05 pm on 23 May 2024.




This image also includes most of the ancient compound crater Desargues, which is an 86 kilometres diameter walled plain which has been struck by two later impactors.  Desargues is shown in full in item  # 102  next month.


Anaximander

Anaximander (610-546 BCE), regarded as the father of astronomy, was a contemporary of Thales and followed his teachings. He agreed that everything had a common origin, but did not agree that it was water. Instead, he said that everything came from ‘ πειρον’ (‘apeíron’, which means ‘the original, indefinite, limitless principle’). From this, four elements of earth, water, air and fire were formed, from which everything else was made. Anaximander was one of the first to differentiate between ‘fixed stars’ and planets. He described the Pole Star, and said the path of the Sun, Moon and planets was tilted to what we call the ‘celestial Equator’, a phenomenon now called the ‘obliquity of the Ecliptic’.

He believed that the Earth was at the centre of the universe, and so stated that, being in such an exalted position, it would have no need of support. He took this further to postulate that our planet was a squat cylinder with a length one-third of its diameter, not floating on Thales’ ocean, but hanging motionless, suspended in space without requiring any physical means of support (right). The world as we know it occupied the upper end. This idea of a free-floating Earth was a marked advance, as all previous cosmogonies described a world that needed to be held up by something, such as pillars or water. However, Anaximander did place the floating Earth fixed at the centre of the universe. He claimed that the Earth was surrounded by an opaque crystalline black sphere that enclosed the air and weather. The celestial bodies moved on this sphere. Outside the sphere was a region of fire. Stars were tiny holes in the sphere through which the fire behind could be glimpsed.      


 

 

           

The First Series of the Lunar Feature of the Month ran from September 2016 to December 2024.

There are 100 features illustrated by 140 lunar images.

 

To access the First Series Archive, click  here .