Lunar Features

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).

The image of #25 Gutenberg in the Lunar Feature of the Month Archive - First Series contains hundreds of sub-kilometre craterlets around the crater Goclenius. Ten of them are indicated by yellow lines in the enlargement seen below. The image was acquired at 5:19 pm on 18 July 2018.

Goclenius (55 kilometres x 54 kilometres). The easiest sub-kilometre craterlet to find in this image is located inside Goclenius, 7 kilometres north of that walled plain's geometric centre. It is shown between two blue lines. Careful measurement of Lunar Reconnaisance Orbiter images shows that the diameter of that craterlet is about 650 metres.

Archive - Second Series

Generally speaking, most telescopic observers have their favourite lunar features, most of which have already appeared in the 100+ images presented in the First Series of 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 observed 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 study. 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 examined 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 western 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 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 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 First Series with those above, and those that follow in Group A ( 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. As most of these "rays" are to the north-east to south-east of the crater, it is obvious that the impactor was travelling at a low altitude from the west (left-hand side).

Key to features 101 to 110 below.

101: January 2025

GROUP A

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 image in a sequence of 50 images to be presented this year, covering the zone of libration from the Moon's North Pole around the north-western limb 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 first series of the Lunar Features of the Month Archive. This image was captured at 9:36 pm on 22 May 2024.

i: 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 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.

Pythagoras has his own crater 370 kilometres west of Philolaus (see # 102 below), in the same northern part of the Moon where we also find craters named after other famous Greek philosophers such as Anaximander, Anaxagoras, Plato, Eudoxus, Calippus, Aristoteles, etc.

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

ii: 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 the next two images.

102: February 2025

GROUP B

This month's feature is a rugged area to the south-west of the Moon's North Pole. It extends west to longitude 63º west and south to latitude 57º north. It includes an ancient walled plain called Anaximander and a spectacular crater called Pythagoras.

This area shares many features with the six images immediately above. This one was captured at 9:51 pm on 22 May 2024.

iii: The conjoined crater plains Anaximander (68 kilometres), Anaximander B (78 kilometres) and Anaximander D (92 kilometres) produce a large flat area to the left (west) of the clearly defined crater Carpenter (60 kilometres) which is obviously much more recent. The tiny craterlet marked '1' in white in this image and the one below serves to link the two images.

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 ‘ἄπειρον’ (‘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.

This area is dominated by the great impact crater of Pythagoras which is 129 kilometres in diameter. It is a middle-aged crater, and it struck the Moon near the north-eastern corner of a much more ancient walled plain called Babbage. This image was taken at 9:57 pm on 22 May 2024.

iv: Pythagoras has a diameter of 129 kilometres. It has a lava-filled flat floor with three spectacular groups of mountain peaks in its centre. The walls of Pythagoras show some of the most spectacular terraces on the Moon. There is a four kilometre craterlet on the northern part of the floor, and a five kilometre craterlet has struck one of the northern terraces. Babbage is a rectangular feature with a distance across the diagonals of 150 kilometres. Its walls have been worn down by small impactors raining down for the last four billion years until they have become hardly recognisable. When the Pythagoras impactor arrived, great quantities of melted rock and rubble were catapulted into Babbage and can be seen overlying the north-eastern quarter of Babbage's floor. The rock melt covering the Moon's surface to the west (left) of Pythagoras indicates that the impactor arrived from the east and travelled at a low level before striking the surface.

Just catching the morning Sun at the top of this image are numerous craters whose walls are illuminated, but whose interiors remain in darkness. Two of these are Cleostratus (63 kilometres) and Boole A (56 kilometres). Two other crater plains identified in this image are Oenopides (68 kilometres) and South (108 kilometres). Both of these are far from the terminator and are well lit.

This area shares many features with the two images immediately above. This one was captured at 8:08 pm on 23 May 2024, the evening after the previous images.

v: The Moon is now less than 4 hours from being Full, and three new craters have become visible near the north-western limb. They are Boole (63 kilometres), Boole H (75 kilometres) and Cremona (86 kilometres). All three are in the zone of libration.

Pythagoras

Pythagoras of Samos (ca. 570-495 BCE) was the first person to describe himself as a philosopher (lover of wisdom). He travelled widely, seeking knowledge from Egypt, Babylon and possibly India, before settling in Croton, Italy. The first true mathematician, he is best known for his famous geometrical theorem regarding right-angled triangles: "The square on the hypotenuse of a right-angled triangle equals the sum of the squares on the other two sides." He began a religious brotherhood called the Pythagoreans, to promote his philosophies. They believed that numbers are the ultimate reality, and everything is related to mathematics. It was he who gave the name kosmos (order, or the interconnectedness of all things) to the universe. He had observed that the North Star appeared higher in the sky when he journeyed north, and lower in the sky when he went south, and came to the conclusion that the Earth is not flat, but is shaped like a sphere. This was a major advance. Since his time, no sensible person has ever believed in a flat Earth, but he also taught that all the planets revolve around a central point with uniform, circular motion, and that the stationary globe of the Earth was located immovable at this central point.

Pythagoras then took this thinking further, postulating that the globe of the Earth is surrounded by a rotating series of eight concentric, crystalline spheres of impenetrable hardness, on which are fixed objects that shine, namely the Sun, Moon, planets and stars. As all the stars appeared to be ‘fixed’ in position, they must all be attached to the furthermost sphere, which must be black. The first seven spheres needed to be transparent so that the stars on the black sphere beyond could be seen. They were all nested together, and moved as one, although they each had small individual motions. Pythagoras’ ideas, quite novel in the sixth century BCE, had a major influence on Plato, and, through him, on all western thought. In his geocentric view of the universe, Pythagoras believed that the concentric crystalline spheres were separated by musical intervals (tones and semitones), and generated musical harmonic scales. He called this the music of the spheres, and claimed to be able to hear it.

In his concept, the musical interval between the Earth (Terra) and the fixed stars (Signifer) had to be a diapason – the most perfect harmonic interval. The individual steps in the sequence were: Earth to the sphere of the Moon = 1 tone; Moon to Mercury = 1 semitone; Mercury to Venus = 1 semitone; Venus to Sun = 1 tone + 1 semitone (3 semitones); Sun to Mars = 1 tone; Mars to Jupiter = 1 semitone; Jupiter to Saturn = 1 semitone, Saturn to the sphere of fixed stars = 1 tone + 1 semitone (3 semitones). The sum of these intervals equals seven tones, the interval covered by the eight notes in an octave.

Pythagoras later produced a novel idea that the Earth might not lie at the centre of the universe, but might itself be in motion, revolving around a ‘central fire’ called Hestia, which was always hidden from us by the bulk of the Earth. The Sun would be a shiny disc also revolving around Hestia, and reflecting the central fire to the Earth.

103: March 2025

GROUP C

This month's feature is the area at the extreme north end of the Oceanus Procellarum (Ocean of Storms). It extends west to longitude 80º west and south to latitude 46º north. It includes an ancient walled plain called Xenophanes and a much more recent crater called Markov.

This image shows the features to the west of those in the previous image. It was taken at 10:03 pm on 22 May 2024.

vi: The crater plains Cleostratus and Oenopides seen near the left margin of the image just above paragraph ' v ' above, now appear at the right margin of this image. Fresh moonscapes around the crater Markov (41 kilometres) and the walled plain Repsold (108 kilometres) have now come into view. The large flat areas in this and subsequent images are part of the extensive lava plain known as the Oceanus Procellarum (Ocean of Storms), which has an area of 2.1 million square kilometres. The complete wall of the large crater plain Xenophanes (121 kilometres) is visible, but its floor remains in shadow except for the illuminated summits of a mountainous spine running north-east to south-west and an illuminated summit on the northern wall of a 35 kilometre crater-plain on the west half of Xenophanes' floor (seen below). The upper left corner of this image shows a black void which is the dark interior of the walled plain Volta (113 kilometres). The outside of the curved southern wall of Volta is seen clearly.

Xenophanes

Xenophanes of Colophon (c. 570 - c.478 BC) was a Greek philosopher, theologian and poet from Ionia who travelled throughout the Greek-speaking world in early classical antiquity. Only fragments of some of his works survive in quotations by later philosophers and scholars. Xenophanes is remembered as one of the most important philosophers in the century before Socrates. A highly original thinker, he sought explanations for physical phenomena such as clouds and rainbows based on actual observations, without references to divine or mythological suggestions or ideas. He distinguished between different forms of real knowledge and mere beliefs, an early instance of epistemology.

The same area of the Moon, photographed at 8:12 pm on 23 May 2024.

vii: In this image, taken 22 hours later, the whole walled plain of Volta has been filled with sunlight, revealing a mountain and two craters on the floor, and another crater, Volta D (20 kilometres), which has impacted on the south-western wall. The far (northern) wall of Volta has been impacted by the secondary crater Regnault (48 kilometres), which also has been revealed by the rising Sun. The left side of this image shows part of the complex floor of the crater-plain Repsold (108 kilometres) which is shown in full in the next four images.

This image shows the features to the south of those in the previous image. It was taken at 10:11 pm on 22 May 2024.

viii: In this image, the walled plain Volta was still in shadow, as was nearby Galvani (80 kilometres). The recent cone crater Dechen (12 kilometres) is isolated in the Oceanus Procellarum. Repsold has a squarish shape, each diagonal approximating 108 kilometres. Its flat floor has numerous craterlets, and is crossed by several V-shaped rilles and some grabens (rift valleys), but these can only be observed a day later if the libration allows. Repsold's north-west corner has been struck by a large impactor, creating a secondary crater called Repsold G (44 kilometres). Near the left margin is a small cone-shaped crater called Repsold T (13 kilometres). It is indicated on this image and three others by the letter T, and can be used to link this image with others in this Group and the next.

The same area of the Moon, photographed at 8:16 pm on 23 May 2024.

ix: The rising Sun which has illuminated the interiors of the craters Volta and Regnault has also revealed details in the interiors of Galvani, Gerard Q Inner and Outer, Repsold and Repsold G. The previously unseen craters Stokes (51 kilometres), Langley (60 kilometres), McLaughlin (79 kilometres) and McLaughlin B (43 kilometres) have also become visible. .

Galvani

Luigi Galvani (1737-1798) was an Italian physician, physicist, biologist and philosopher who studied what was then called ‘medical’ or ‘animal electricity’. This field emerged in the middle of the 18th century, following electrical researches and the discovery of the effects of electricity on the human body by various European scientists in the.1770s. In 1780, using a frog, he discovered that the muscles of dead frogs' legs contracted or twitched when struck by an electrical spark.This was an early study of bioelectricity, following experiments by John Walsh and Hugh Williamson. He concluded that every animal cell has an electric potential, and that biological electricity was distributed around a body by ‘animal electric fluid’. This fluid existed only in living creatures, so it was believed for a time that electricity was only to be found in living beings.

Volta

Alessandro Giuseppe Antonio Anastasio Volta (1745-1827) was an Italian chemist and physicist who was a pioneet of electricity and power, and is credited as the discoverer of methane. At first, he accepted ‘animal electricity’ and was among the first scientists who repeated and checked Galvani’s experiments. However, he began to doubt that the contractions were caused by specific electricity intrinsic to the animal’s legs or other body parts. He experimented with various chemicals similar in nature to the so-called ‘animal electric fluid’ and invented the ‘voltaic pile’ (a multi-cell battery) in 1799. He therefore proved that electricity could be generated chemically in a laboratory and debunked the theory that electricity was generated solely by living beings. Volta's invention sparked a great amount of scientific excitement and led others to conduct similar experiments, which eventually led to the development of the field of electrochemistry.

Volta drew admiration from Napoleon Bonaparte for his invention, and was invited to the Institute of France to demonstrate his invention to the members of the institute. Throughout his life, Volta enjoyed a certain amount of closeness with the emperor who conferred upon him numerous honours. Volta held the chair of experimental physics at the University of Pavia for nearly 40 years and was widely idolised by his students. The SI unit of electric potential, e.g. “240 volts” is named the "volt" in his honour.

Galvani did not agree totally with Volta’s discoveries, but both men respected each other and corresponded regularly. When Volta built the first electric circuits using battery power, he gave a nod to his rival by coining the term “Galvanism” for a direct current of electricity produced by chemical reaction.

104: April 2025

GROUP D

This month's feature is a rugged area on the lunar limb about halfway between the Moon's North Pole and its Equator. It extends west to longitude 87º west and south to latitude 37º north. It includes an ancient walled plain called Lavoisier and a much more recent crater called Harding.

This image was taken at 10:18 pm on 22 May 2024.

This image shows the features to the south of those in the image described in paragraph ' x: '.

This image shows the features to the west of those in the previous image. It was taken at 8:19 pm on 23 May 2024.

x: This image adjoins the one listed as ' x: ' in GROUP C. Both include the small crater marked with a letter T(Repsold T) and the crater Dechen. The walled plain Gerard (91 kilometres) has a very rugged floor, with numerous hills and many craterlets with diameters between 3 and 4 kilometres. Adjoining the north-west wall of Gerard is a huge walled plain called Gerard Q (192 kilometres). It is known as Gerard Q Outer, for there is in its centre a circular feature called Gerard Q Inner, which has a diameter of 67 kilometres). This feature is volcanic and has in its western half extremely rugged hills with floor fractures, while in its eastern half we find a dark-coloured flat area which was once a lake of molten basaltic magma.

South of Gerard is a flat-floored crater-plain named Von Braun (61 kilometres). West of it is a similar but smaller crater called Lavoisier E (49 kilometres). Like many others in their vicinity, the floors of these two craters contain many rilles and grabens. Isolated in the Oceanus Procellarum are Harding (23 kilometres) and Dechen.

This image shows the features to the south-west of those in the previous image. It was taken at 10:29 pm on 22 May 2024.

xi: The largest crater-plain in this image is Lavoisier (90 kilometres) which, like its neighbours Von Braun, Lavoisier A, Lavoisier E, Lavoisier H, Bunsen, Volta, Repsold and Repsold G, has a flat floor which is crossed by numerous rilles and grabens. Most other craters in the area do not have these volcanic features. There is an interesting feature just north of the centre of Lavoisier. It is a 5 kilometre diameter unnamed concentric cone crater, in which one impactor has created the original crater, and a second impactor has landed in the exact centre of that crater, giving the impression of a bulls-eye or doughnut. Such concentric craters are quite rare, but two which have been photographed and can be found on this website appear as images # 14 (Hesiodus A) and # 41 (on the eastern side of the Humboldt walled plain) in the Lunar Features of the Month Archive - First Series.

This image shows the features to the west of those in the previous image. It was taken at 8:26 pm on 23 May 2024.

xii: The rising Sun which has previously revealed the craters Gerard, Harding and Von Braun (see image ' xi: ') has now illuminated the craters Bunsen (53 kilometres), Bunsen A (39 kilometres), Bunsen B (20 kilometres, Bunsen C (18 kilometres), Lavoisier E (49 kilometres) and Avicenna G (26 kilometres). All six of these are in the zone of libration. Lavoisier A (28 kilometres) has a rugged floor with numerous rilles, and one major terrace which runs for a fifth of the inner circumference.

Bunsen

Click here for a pdf file telling the remarkable story of how Robert Bunsen and Gustav Kirchhoff discovered the mysterious "barcode of the stars" in 1859, which enabled us to find out what stars are made of.

Gerard

Alexander Gerard (1792-1839) was a Scottish army officer in India, and an early surveyor and explorer of the Himalayas. During the surveys he made in the Himalayas, he ascended heights previously believed to be inaccessible, and penetrated into Tibet as far as the frontier with China. Our earliest information of the structure of the Himalayan ranges come from his explorations in 1821, when his team climbed to heights of up to 19 400 feet (5913 metres).

Harding

Karl Ludwig Harding (1765-1834) was a German astronomer who discovered the minor planet Juno in 1804. It was the third asteroid to be found, after Ceres (by Piazzi) and Pallas (by Olbers). In addition to Juno, he discovered three comets and the variable stars; R Virginis, R Aquarii, R Serpentis and S Serpentis. He also found some new nebulae, one being the Helix Nebula.

Von Braun

Wernher Magnus Maximilian Freiherr von Braun (1912-1977) was a German-American aerospace engineer. He was the leading figure in the development of rocket technology in Nazi Germany, and later a pioneer of rocket and space technology in the United States.

As a young man, von Braun worked in Nazi Germany's rocket development program. He helped design and co-developed the V-2 rocket at Peenemünde during World War II. A V-2 became the first artificial object to travel into space on 20 June 1944. Over 3000 V-2 rockets were fired at London and Antwerp in the final seven months of the war, resulting in the deaths of over 5000 citizens. Following the war, von Braun was secretly moved to the United States, along with about 1600 other German scientists, engineers and technicians. He worked for the United States Army on an intermediate-range ballistic missile program, and developed the rocket that launched the United States' first space satellite Explorer 1 in 1958. In 1960, his group was assimilated into NASA, where he served as director of the newly formed Marshall Space Flight Center and as the chief architect of the Saturn V super-heavy-lift launch vehicle that propelled the Apollo spacecraft to the Moon from 1968 to 1972. In 1967, von Braun was inducted into the National Academy of Engineering, and in 1975, he received the National Medal of Science.

Von Braun was a controversial figure, widely seen as escaping justice for his awareness of Nazi war crimes due to the Americans’ desire to beat the Soviets into space during the Cold War. He was decorated by Adolf Hitler twice. Despite his faults, he can be described as the “father of space travel”, the “father of rocket science”, or the “father of the program to put a man on the Moon”.

Lavoisier

By the second half of the eighteenth century, the ancient idea of the universe being composed of four ‘elements’ (earth, water, air and fire) had been completely laid to rest. Robert Hooke had shown a century earlier that fire was not an element but a chemical process. The metals of copper, lead, gold, silver, iron, carbon, tin, sulphur, mercury, zinc, arsenic and antimony had been known since antiquity but were thought to be merely ingredients of earth. Now they were understood to be individual elements in their own right, so earth was not an element but many diverse compounds. Phosphorus had been recognised in 1669, and cobalt, platinum, nickel, bismuth and magnesium were isolated by 1755. Hydrogen was first artificially produced in 1671 by Robert Boyle (1627-1691), who discovered and described the reaction between iron filings and dilute acids, which results in the production of a gas. In 1766, Henry Cavendish (1731-1810) was the first to recognise hydrogen as a discrete substance, by naming the gas from the metal-acid reaction “inflammable air”, as it ignited explosively if a flame was introduced. He found in 1781 that the gas produced water when burned. He is usually given credit for the discovery of hydrogen as an element, but it remained without a name.

Oxygen was first discovered by the Swedish pharmacist Carl Wilhelm Scheele (1742-1786). He produced oxygen gas by heating mercuric oxide and various nitrates in 1771-72. Scheele called the gas “fire air” because it was the only known supporter of combustion, and wrote an account of this discovery in a manuscript entitled Treatise on Air and Fire, which he published in 1777. In the same period, the English clergyman Joseph Priestley (1733-1804) used sunlight to heat mercuric oxide and saw that candles burned brighter in the gas produced and breathing it made him feel light-headed. Antoine Lavoisier (1743-1794) was also studying this gas and named it oxygen (ὀξύς oxys meaning “acid” or “sharp tasting” and γενής genes meaning “creator”). The discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford (1749-1819) in 1772, who called it “noxious air”, though he did not recognise it as an entirely different chemical substance or element. The name nitrogen was given to it in 1790 by the French chemist Jean-Antoine Chaptal (1756–1832), from the French nitre (potassium nitrate or saltpetre).

As air was now known to be a mixture of gases, mainly nitrogen and oxygen, air lost its position as an ‘element’. In 1783 Antoine Lavoisier, in co-operation with the mathematician Pierre-Simon de Laplace (1749-1827), reproduced Cavendish’s finding that water is created when “inflammable air” is burned. They synthesised water by burning jets of “inflammable air” and oxygen in a bell jar over mercury. This revealed that water also was not an element, but a compound of two gases. Lavoisier gave the “inflammable air” the much more suitable name of hydrogen (ὑδρο hydro meaning “water” and γενής genes meaning “creator”).

Lavoisier helped develop the first comprehensive list of elements (of which there were 29), and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and discovered that, although matter may change its form or shape, its mass always remains the same. His wife and laboratory assistant, Marie-Anne Paulze Lavoisier (1758-1836) became a renowned chemist in her own right.

105: May 2025
GROUP E

This month's feature is a rugged area south of that shown in GROUP D above. It extends west to longitude 92º west and south to latitude 23º north. It includes an ancient walled plain called Rontgen and a much more recent crater called Aston.

This image shows the features to the south of those described in paragraph ' xii: ' above. It was taken at 8:47 pm on 17 March 2022.

Ulugh Beigh (55 kilometres) is a deformed crater which has been flooded with lava from the Oceanus Procellarum through a small breach in its eastern wall, to create a flat floor.

Every feature west of Ulugh Beigh (further away) is in the zone of libration.

xiii: The huge walled plain Lorentz was just over the horizon due to libration when this image was taken at 8:30 pm on 23 May 2024. Its diameter is 312 kilometres, and it encloses many other crater plains that have individual names, such as Nernst (116 kilometres), Rontgen (126 kilometres), Avicenna (74 kilometres) and Laue (87 kilometres). Lorentz should therefore be described as a basin, like Bailly (303 kilometres) or Grimaldi (222 kilometres). The two small white craterlets just above the lower left-hand corner of this image (marked with a white '2' ) reappear in the following image just above the lower right-hand corner, and so serve to link the images.

Ulugh Beigh

Ulugh Beigh (or Beg, 1394-1449) was descended from Mongol warlords. He was a grandson of King Timur (also known as Tamerlane) but he valued knowledge more than power. While still a boy he visited the ruins of al-Tusi’s Marāgha Observatory and was inspired by it. On turning 16 in 1409, his father granted him a province including the city of Samarkand. He built the world’s largest observatory there in 1428 and devoted himself to studying the sky. It was a three-storeyed drum-shaped building 50 metres in diameter and 37 metres high, perched on top of a rocky knoll. Travellers on the Silk Road marvelled at it and its fame spread. Inside his observatory, he built a huge mural quadrant (the bigger the quadrant, the better the accuracy). Starting below ground level, it was a quarter-circle on edge, reaching to the top of the observatory building. Two parallel strips of marble ran around the curved section, on which were inscribed numbers showing degrees from the horizontal. The walls were lined with marble. In 1437 Ulugh Beigh used his observatory to produce a catalogue of 994 stars called the Zij-i-Sultani, the best since the time of Ptolemy.

Ulugh Beigh cast a horoscope for his eldest son, but the son was so perturbed by it that he murdered his 56-year-old father. Religious conservatives then destroyed the observatory. The underground section of the great quadrant was filled in with rubble and forgotten. It was found and excavated in the 20th century. Protected now, it is part of a huge museum in Samarkand, dedicated to the works of Ulugh Beigh.

Rontgen

Wilhelm Conrad Röntgen (1845-1923) was a German physicist who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range known as X-rays or Röntgen rays, an achievement that earned him the inaugural Nobel Prize in Physics in 1901. In honour of Röntgen's accomplishments, in 2004, the International Union of Pure and Applied Chemistry (IUPAC) named the element No. 111 “roentgenium” (a radioactive element with multiple unstable isotopes) after him. The non-SI unit of radiation exposure, the roentgen (R), is also named after him.

Röntgen's original paper, "On A New Kind of Rays" (Ȕber eine neue Art von Strahlen), was published on 28 December 1895. On 5 January 1896, an Austrian newspaper reported Röntgen's discovery of a new type of radiation. Röntgen published a total of three papers on X-rays between 1895 and 1897. Today, Röntgen is considered the father of diagnostic radiology, the medical process which uses imaging to diagnose disease.

This image shows distant features to the south of those in the previous image. It was taken at 8:38 pm on 23 May 2024.

xiv: The craters Bartels (55 kilometres), Voskresenskiy (51 kilometres) and Struve H (21 kilometres) and their neighbours are all in the zone of libration. The great walled plains Struve and Russell are described in paragraph ' xv: ' below.

106: June 2025
GROUP F

This month's feature is a group of three adjoining walled plains, all three being over 100 kilometres in diameter and having their interiors swamped by lava flows from the Oceanus Procellarum. The area photographed extends west to longitude 93º west and south to latitude 16º north, and covers the craters from Struve to Dalton.

This image shows the features to the east of those in the previous image. It was taken at 10:36 pm on 22 May 2024.

xv: This image shows three huge walled plains. The western two are conjoined with the parts of their walls between them being completely obliterated. They are Russell (105 kilometres) and Struve (171 kilometres). Careful examination will reveal the small gap in Struve's eastern wall where molten lava from the Oceanus Procellarum has found its way into Struve and then into Russell, flooding them both until the lava surface inside them has reached the same level as the flat plain outside. A similar flooding also occurred with Eddington (134 kilometres), except that much of the eastern wall of that crater has been carried away by the molten lava. There had been a small 12 kilometre crater inside the floor of ancient Eddington, but it was swamped by the incoming lava flow. However, portions of its wall were higher than the final lava level, and these still can be seen as a ghost crater called Eddington P. Although these three walled plains appear elliptical, such foreshortening is merely a perspective effect due to their position near the Moon's limb. Pictures taken by the Lunar Renaissance Orbiter series of satellites from directly overhead of these walled plains show that they are all almost perfectly circular.

Russell

Henry Norris Russell (1877-1957) was an American astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung-Russell Diagram or H-R Diagream of stellar evolution in 1910. This diagram charts the magnitude of stars on the vertical axis (brightest to the top) against the colour of stars on the horizontal axis (hottest blue ones to the left, coolest red ones to the right). This diagram is also known as the Colour-Magnitude Diagram. When plotting a large number of stars on this Diagram, it is found that the great majority of them cluster along a diagonal line, from the upper left-hand corner (hot, blue giant stars) to the lower right-hand corner (faint red dwarfs). Russell called this line the "main sequence" and stars on this line "main sequence stars". He said it was an "evolutionary track" and stars would progress along it as they aged. Therefore, a star's position on the main sequence indicated its evolution. This was a mistake - see Eddington below.

Struve

Friedrich Georg Wilhelm von Struve (1793-1864) is best known for his observations of double stars, which he carried on for many years. Although double stars had been studied earlier by William Herschel, John Herschel and Sir James South, Struve outdid any previous efforts. While working as the Director of the Dorpat Obsevatory, he obtained in 1824 a refracting telescope with an aperture of 24 cm (about 9.5 inches) made by Joseph von Fraunhofer, said to be a masterpiece of optical and mechanical perfection. With this telescope, known as the Great Refractor, Struve discovered a very large number of double stars. In 1827 published his double star catalogue Catalogus novus stellarum duplicium. Stars of his catalogue are sometimes indicated by the Greek letter sigma, Σ. Thus, 61 Cygni is also designated as Σ 2758.

Since most double stars are true binary stars rather than mere optical doubles (as William Herschel had been the first to discover), they orbit around their common barycentre and slowly change position over the years. Thus Struve made micrometric measurements of 2714 double stars from 1824 to 1837 and published these in his work Stellarum duplicium et multiplicium mensurae micrometricae. Struve carefully measured the "constant of aberration" in 1843. He was also the first to measure the parallax of the star Vega, although Friedrich Bessel had been the first to measure the parallax of a star, 61 Cygni. The Great Refractor was fully restored to pristine condition in 1993.

Eddington

Arthur Stanley Eddington (1882-1944) was Britain's foremost astrophysicist from 1910 to 1930. He had read Einstein's 1911 paper On the Influence of Gravity on the Propagation of Light, in which it was claimed that a ray of starlight passing close by the Sun would be deflected by the Sun's gravity, so that the star's position in the sky would be altered by about 0.85 arcseconds. Willem de Sitter managed to send a copy of Einstein's General Theory of Relativity of 1915 (that defined gravity as curvature in space) to Eddington in 1916. He read it avidly, and saw that Einstein had corrected the deflection of starlight in the vicinity of the Sun to 1.7 arcseconds.

The Astronomer Royal Sir Frank Dyson suggested to him in 1917 that the theory of relativity could be tested during the 29 May 1919 total solar eclipse, by seeing if the mass of the obscured Sun would bend the space in its vicinity, thereby displacing the light of stars in the same line of sight by the predicted amount. He said that the eclipse was especially fortuitous as, not only was its totality unusually long (six minutes), but close to the Sun's limb would be numerous stars, and the bright Hyades cluster was less than six degrees away. Eddington organised an expedition and, in the event, the results obtained did not support Newton's theory of gravitation, but instead supported Einstein's new theory - the Sun had deflected the starlight by from 1.6 to just over 1.7 arcseconds. Arthur often later said that, as he measured the photographic plates, when he realised that Einstein was right it was "the greatest moment of my life". This sensational news catapulted the little-known Einstein onto the world stage, and the rest is history.

Arthur criticised Henry Norris Russell's use of the term "main sequence" with respect to the H-R Diagram described above. He said that it was a misnomer, as a star condensing from a nebula would arrive on the main sequence at a certain point according to its mass. It would remain at that point for most of its existence, until it became unstable towards the end of its life. Then, if it were a dwarf star like the Sun, it would grow much larger and move off the main sequence and onto the giant branch. It would never move ALONG the main sequence. Russell abandoned his "evolutionary track" idea in 1927, but the flawed term "main sequence" is still in use, and is applied to about 95% of stars.

This image shows the features to the south of those in the previous image. It was taken at 10:43 pm on 22 May 2024.

The image above partially shows three new craters, Dalton (61 kilometres), Balboa (70 kilometres) and Balboa A (47 kilometres), all of which are in the zone of libration. The following image, taken the day after the one above, shows how new craters are illuminated as Full Moon approaches.

This image shows the features to the west of those in the previous image. It was taken at 8:42 pm on 23 May 2024.

New craters revealed are Einstein, Einstein A and Moseley (90 kilometres).

107: July 2025

GROUP G

This month's feature is the area extending west to longitude 95º (into the libration area) and from the crater Balboa south to Bohr. It includes an ancient walled plain called Einstein and a much more recent crater called Krafft.

This image was taken at 8:45 pm on 23 May 2023, which was 3 hours 9 minutes before the Moon was officially Full that month.

xvi: This image shows four new craters revealed by the terminator as Full Moon approaches. They are Bohr (71 kilometres), Vasco da Gama (96 kilometres), Einstein (171 kilometres) and Einstein A (51 kilometres). Einstein is a large walled plain that is very old and degraded. Through mere chance, a much later impactor struck Einstein exactly in its centre, creating the much crisper-looking crater Einstein A. All of these features are in the zone of libration, and rigorous planning is necessary if they are to be observed. One must record when they will be at their greatest libration east, and when they will be correctly lit by the Sun. It is necessary that a date for observing will satisfy both criteria. Along the bottom of the image can be found streaks of light-coloured material called impact rays. One of these rays passes tangentially the crater Krafft (51 kilometres). These rays are from the crater Glushko (40 kilometres), just out of the photographic frame. Glushko, however, is featured on the next image below.

Einstein

Click here for a pdf file explaining how Albert Einstein produced his Special Theory of Relativity in 1905, and his General Theory of Relativity in 1915. These theories changed the world forever.

Balboa

Vasco Núñez de Balboa (1475-1519) was a Spanish explorer, governor and conquistador. He is best known for crossing the Isthmus of Panama from the Atlantic to the Pacific Ocean in 1513, becoming the first European to have seen the Pacific from the New World.

Vasco da Gama

Vasco da Gama (1460-1524) was a Portuguese explorer who was the first navigator to sail from Portugal south down the west coast of Africa, round the Cape of Good Hope, and then north along the African east coast, past Madagascar to Zanzibar. Then he contracted the services of a pilot familiar with the monsoon winds in the Arabian Sea, who took them east across the sea to the Indian sub-continent. This voyage was important as it discovered a sea route from Europe to India and the Orient.

Bohr

Click here for a pdf file describing the work of Niels Bohr and others in the new field of Quantum Physics and Quantum Mechanics in the mid-1920s.

108: August 2025

GROUP H

This month's feature covers the area extending to longitude 92º west (into the libration zone) and extending south from 12º north to 2º south latitude. It includes part of an ancient walled plain called Riccioli and a much more recent crater called Glushko.

This image centred near the crater Glushko (40 kilometres) shows how detritus from the explosion is spread around the point of impact for hundreds of kilometres.

xvii: Other features are the craters Sundman (40 kilometres), Olbers (75 kilometres) and Hedin A (60 kilometres). A notable feature near the upper right of the image is the Vallis Bohr (Bohr Valley). This begins near the north rim of the 71 kilometre crater Bohr, and travels for nearly 100 kilometres due south towards the Mare Orientale (Eastern Sea), with which it may be related. It finishes near the craterlet Sundman J (10 kilometres).

This image was taken at 8:54 pm on 23 May 2024.

109: September 2025

GROUP I

This month's features include the three walled plains named after the 17th century lunar cartographers Hevelius, Grimaldi and Riccioli. It covers the area near the limb to longitude 76º west, and from latitude 6º north to 9º south.

In 1651, Giovanni Riccioli named the two largest walled plains in the above image after himself and Francesco Grimaldi (his colleague who actually drew the lunar map), and gave a nod to their rival Johannes Hevelius who had published a lunar map in 1647, but had named lunar features after earthly ones. For example, Hevelius had named a huge lava plain the "Mediterranean Sea" and a spectacular crater "Mount Etna" - Riccioli changed these confusing names to "Mare Imbrium" and "Copernicus".

Northern Section. The lunar Equator passes between the walled plain Hevelius and the crater Lohrmann, and south (left) of the crater Riccioli CA.

Southern section.

The above image was taken on May 25, 2021 at 7:46 pm.

110: October 2025

This month we will look at a group of three volcanoes located at the mare / highlands boundary where the north-east border of the Oceanus Procellarum (Ocean of Storms) meets the Mare Imbrium (Sea of Rains).

The three volcanic domes inside the blue circle are 120 kilometres north of the 17 kilometre impact crater Gruithuisen (lower-left corner). This image was taken on September 2, 2017 at 10:22 pm.

Mons Gruithuisen Gamma is the largest of the three volcanoes, and is the second-largest volcanic dome on the Moon after the Valentine Dome (30 kilometres diameter, near the 3 kilometre craterlet Linne ( see item # 84 in the Lunar Feature of the Month - First Series ). The diameter across the base of Mons Gruithuisen Gamma is 20 kilometres, and it is 1500 metres high. The 800 metres diameter caldera at its summit is at the exact centre of the blue circle. There is a 650 metres impact craterlet on the volcano's north-eastern slope, and its surface has many other small craterlets. A delicate rille at the limit of resolution runs southward along the eastern slope of this mountain.

East-south-east of Mons Gruithuisen Gamma (underneath it in the picture) is a second dome known as Mons Gruithuisen Delta. It is slightly smaller in size, not quite so high, and has no summit caldera. There is a small 200 metre craterlet near the summit, but there is no agreement as to whether it is of volcanic or impact origin. About 15 kilometres north-west of Mons Gruithuisen Gamma is a smaller volcano called Mons Gruithuisen NW (north-west). It is less dome-like and much steeper in its slope. We can get some idea of the extraordinary steepness and heights of the three volcanic domes in comparison with the surrounding hills by examining the length of their shadows, which run westwards (towards the upper left-hand corner). Midway between Mons Gruithuisen Delta and the Gruithuisen crater is a low volcanic crater-covered, flattened dome, which has two sharp peaks whose shadows tend to rival the other three.

Key to features 111 to 120 below.

111: November 2025

This month we will look at at two spectacular groups of mountains known as the Montes Recti (Straight Range) and the Montes Teneriffe (Teneriffe Mountains).

The Montes Recti and the Montes Teneriffe are located in the northernmost extremity of the Mare Imbrium (Sea of Rains). This image was taken on 22 May, 2021.

The Montes Recti (Straight Range) is a remarkable oddity on the Moon. It is composed of 25 peaks arranged in a 90 kilometres x 20 kilometres straight chain. There seems to be a possible alignment of individual peaks in a north-south direction, and the major axis of the whole group is basically west-east. The largest mountain is at the eastern end, but it is disfigured by a 7.3 kilometre impact crater called Montes Recti B.

The Montes Teneriffe (Teneriffe Mountains) is a group of mountains about 100 kilometres south-west of the walled-plain Plato. Like the Montes Recti, their bases have been swamped by the great lava flows from the Imbrium Event - see item # 12 of the Lunar Feature of the Month - First Series. Unlike the Montes Recti, the Teneriffe Mountains are not contiguous, but appear as one elongated line of mountains plus four separate blocks of different sizes, so that there are six main summits emerging from the lava of Mare Imbrium. A seventh summit, Mons Pico, lies outside the bottom right-hand corner of the above image, but can be seen in the third image of item # 12 of the Lunar Feature of the Month - First Series.

112: December 2025

This month we will look at at a fine cluster of mountains known as the Montes Alpes (Alps).

The Montes Alpes forms the north-eastern boundary of the Mare Imbrium (Sea of Rains). The image was taken on September 9, 2018 at 7:43 pm.

See item # 12 of the Lunar Feature of the Month - First Series.

The Montes Alpes is a mountainous area that runs in a south-south-easterly direction between the large walled-plains of Plato and Cassini. It is 250 kilometres long, and the width varies between 150 kilometres in the north to 50 kilometres in the south. The height of the mountains averages 2500 metres, but midway along its length the highest peak, Mont Blanc (White Mountain) reaches a height of 3600 metres. The western side of the Alps is bounded by the Mare Imbrium lava plain, and its eastern side by a rugged hilly area composed of detritus from the Imbrium Event (see text in item # 12 of the Lunar Feature of the Month - First Series ).

This image and that below were taken at 8:19 pm on 2 August 2017.

One third of the distance from the northern end to the southern, a magnificent valley 130 kilometres long (called the Vallis Alpes or Alpine Valley) divides the mountains into two groups. The northern group consists of about 20 peaks of various sizes clustered in an area measuring 130 kilometres east to west, and 55 kilometres north to south. There are six small flat areas between the peaks. The southern group is more-or-less linear, with about 24 peaks stretching from the Alpine Valley to two promontories at the southern end, the Promontorium Deville and the Promontorium Agassiz. This valley is shown in its entirety above and below.

The Vallis Alpes runs east-north-east from near the Mare Frigoris (Sea of Cold) to the Mare Imbrium which it reaches via a narrow pass between two of the Alps. The Valley averages 11 kilometres in width and has a flat floor between raised cliffs on each side. A delicate rille between 500 and 700 metres wide runs along the valley floor, and it easily seen in the image above. This rille averages 78 metres deep. ( See item # 12 of the Lunar Feature of the Month - First Series ).

113: January 2026

This month we will look at a spectacular walled plain near the crater Tycho. This is Longomontanus, named after Tycho Brahe's faithful assistant.

This image shows the 146 kilometre diameter walled plain Longomontanus, which lies about 160 kilometres south-west of Tycho. This image was taken at 7:19 pm on 19 August 2021. South is to the top.

Longomontanus is an ancient crater in the Moon's southern highlands. Its diameter is 146 kilometres. Its high walls are severely degraded with many radial valleys. A landslip on the western wall has produced one small terrace. The floor is large and flat with little damage, except for two small craters near the western wall (right-hand side), Longomontanus L (16 kilometres) and Longomontanus M (10 kilometres). There is a small mountain group offset from the centre of the floor to the south-west. A double ghost-crater is seen on the floor, adjoining the eastern wall. The floor also has numerous craterlets, some surrounded by small white haloes, indicating that they are recent impacts.

This area is one of the most spectacular on the Moon. Longomontanus is surrounded at distances of roughly 150 kilometres by Clavius # 1 , Tycho # 18 , Bayer and Schiller ( both appearing as # 63 ) , and Maginus # 69 , all of which are found in detail in the Lunar Features of the Month Archive - First Series.

This image was taken at 9:44 pm on 29 December 2017.

Longomontanus

The second version of the ‘Tychonic’ geo-heliocentric theory of 1587 was popularised after his death by Christen Sørensen Longberg (Longomontanus, 1562-1647), Tycho Brahe’s loyal disciple, in his book Astronomia Danica (Danish Astronomy) of 1622. Longomontanus had joined Tycho in 1589 and had been been with him for the last eight years that Uraniborg and Stjerneborg were operational, and for two years in Prague. He repeated that the Tychonic theory retained the concept of transparent spheres, and confirmed Tycho’s conclusion that they were not solid but made of a permeable fluid, and able to pass through and intersect each other without hindrance. Longomonanus’ book made the Tychonic system acceptable to the Catholic church in the 17th century as an alternative to the Copernican system which they condemned. The Jesuits taught it in their mathematics courses as it had all the advantages of the Copernican system without requiring that the Earth itself turn or move. This meant that it did not contradict scripture. By the mid-1600s, most Catholic countries had abandoned Ptolemy for the second Tychonic system, while most Protestant countries endorsed the Sun-centred system of Copernicus.

114: February 2026

This month we will look at a battered crater near the walled plain Posidonius. This is Kirchhoff, named after Robert Bunsen's famous colleague.

This image was taken at 5:46 pm on 15 September 2018.

The crater Kirchhoff is quite ancient and heavily damaged. Its diameter is 25 kilometres.

Kirchhoff is a very old crater which dates from the Pre-Imbrium period (older than 3.9 billion years). It is located in a rugged highland area between the Mare Serenitatis (Sea of Serenity) and the Mare Crisium (Sea of Crises), at latitude 30.3º North and longitude 38.8º East. It has normal walls in the northern half, but those on the southern side are demolished almost beyond recognition. There is a small canyon disfiguring the northern half of the floor, which trends from north-west to south-east. It is six kilometres long and two kilometres wide, and has steep walls.

Kirchhoff

Click here for a pdf file telling the remarkable story of how Robert Bunsen and Gustav Kirchhoff discovered the mysterious "barcode of the stars" in 1859, which enabled us to find out what stars are made of. See also item #104 above.

115: March 2026

This month we will look at an ancient walled plain called Darwin.

This image was taken at 8:49 pm on 25 May 2021.

The walled plain Darwin has a diameter of 131 kilometres. The floor is more or less flat, with numerous hills and a deformed ghost crater in the southern section. A straight graben crosses the floor, beginning outside Darwin near the small impact rater Cruger B. It crosses into Darwin through the north-north-western wall, and immediately turns south-east. As it crosses Darwin, a second and less spectacular graben has formed on the main one's western side, and the two of them run parallel and cross Darwin's eastern wall together, about five kilometres apart. The two grabens are known as the Rimae Darwin. They continue on an east-south-east heading across a small flat area, the distance between them widening, until they connect with the southern end of a larger and deeper rift valley, the Rima Sirsalis, which has a width of three kilometres, and a length variously stated to be from 330 to 400 kilometres long. ( See item # 86 in the Lunar Feature of the Month Archive - First Series ).

North of Darwin is a small crater named Cruger, which is perfectly circular, with a diameter of 46 kilometres. It has a flat floor of dark, hardened basaltic lava, which must have forced its way to the surface, soon after an impactor created Cruger. This image reveals only one three-kilometre craterlet on the floor and some faint light-coloured patches, although spacecraft looking vertically down have revealed at least 80 tiny craterlets dotted around the floor. There are two landslips, one on the western wall and one on the southern. These provide terraces, each one leading from the raised crater rim directly down to the dark floor.

116: April 2026

This month we will look at two ancient walled plains called Lagrange and Piazzi.

This image was taken at 7:58 pm on 25 May 2021. It covers nearly four times the area of the two images described last month.

Just left of centre of this image may be found an 88 kilometre diameter walled plain called Byrgius. An impactor has struck squarely on the eastern rim of this walled plain and created a 19 kilometre crater called Byrgius A. A remarkable feature of Byrgius A is the spectacular ray ststem radiating in all directions for hundreds of kilometres, but especially towards the west. Whereas these rays can be faintly discerned in the picture above, at the time of Full Moon they appear much brighter and are easily observed. This is true for all lunar ray systems, and those centred on the craters Tycho ( # 18 ) and Kepler ( # 83 ) in the Lunar Feature of the Month Archive - First Series are two well-known examples.

Henry Freres

The crater Henry Freres (Henry Brothers) is named after Paul and Prosper Henry, two French opticians and astronomers who worked on the Carte du Ciel (Chart of the Sky) star catalogue, a major project begun in 1877 to use the new photographic processes with glass plates and time exposures to determine the positions of millions of stars. 22 observatories around the world agreed to take part and were supplied with 13-inch (32 cm) astrographic lenses, half of which were built by the Henry brothers in Paris, and the others made by Howard Grubb in Dublin. Each observatory would mount the lens in a tube to make a refractor telescope, and fit it on a suitable mount. The project was organised by Amédée Mouchez, Director of the Paris Observatory (see item # 101 above. Strict guidelines were provided to observatories so that all the photographic plates would be of the same standard so that they could be matched up with each other. Work began immediately and the astronomers sent in their data well into the 20th century. In Australia, the government observatories at Perth, Melbourne and Sydney took part. Sydney was the second-highest contributor with 430 000 stars measured by 1948.

As new observatories with bigger telescopes were being built everywhere in the 20th century, and photographic techniques were improving all the time, soon the early results for the Carte du Ciel were seen to be inadequate and the project found itself outdated. Most astronomers were interested in galaxies, not star positions, and the vast amount of work produced in determining the star positions was regarded as having produced just a small scientific benefit. But today, astronomers are very much indebted to this great effort because these century-old star positions can now be compared with their new positions collected between 1989 and 1993 by the European Space Agency’s Hipparcos satellite (High Precision Parallax Collecting Satellite). This new use for the old data has enabled us to determine how the positions of 2.5 million stars have changed over the years, and thereby to derive with high accuracy the proper motions of those 2.5 million stars.

Specifically, the Carte du Ciel Astrographic Catalogue positions were transferred from the decades-old printed volumes into machine-readable form. This was undertaken at the Sternberg Astronomical Institute in Moscow between 1987 and 1994. The data were then reduced anew at the US Naval Observatory in Washington, using the reference stars measured by the Hipparcos astrometry satellite. The 120 000 highest-accuracy stars from the Hipparcos Catalogue were used to establish a detailed reference framework at the various epochs of the Astrographic Catalogue plates, while the 2.5 million stars in the Tycho Catalogue provided a dense reference framework to allow the plate distortions to be accurately calibrated and corrected. The proper motions of all the Tycho Catalogue stars could then be derived, mainly thanks to the Astrographic Catalogue, but additionally using star positions from more than 140 other ground-based catalogues. Aside from the 120 000 stars of the Hipparcos Catalogue itself, the resulting Tycho-2 Catalogue compiled at Copenhagen University Observatory is now the largest, most accurate and most complete star catalogue of the brightest stars in the sky. It is currently the basis for deriving positions for all the stars which are fainter.

Sean Urban of the US Naval Observatory said in 1998: “The history of the Astrographic Catalogue project is one of dedicated individuals devoting tedious decades of their careers to a single goal. Some believe it is also the story of how the best European observatories of the 19th century lost their leadership in astronomical research by committing so many resources to this one undertaking. Long portrayed as an object lesson in over-ambition, the Astrographic Catalogue has more more recently turned into a lesson in the way that old data can find new and unexpected uses.”

The crater Henry is named after Joseph Henry (1797-1878), an American physicist who investigated electromagnetism. He invented the electric relay and helped develop electric motors.

The left margin of the above image adjoins the right margin of item # 97 in the Lunar Feature of the Month Archive - First Series, which is reproduced below. The craters Vieta, Lagrange C and Lagrange K appear in both images.

Two straight valleys are shown, running in a south-south-east direction from the centre of the Mare Orientale impact basin. They are marked as V.B. ( Valles Baade or Baade's Valley ) and V.I. ( Valles Inghirami or Inghirami Valley ). Two arrows indicate the direction taken by the impact blast that created the valleys. As the blast was widespread, many other features in the upper part of the image show similar linear damage due to the same explosion. As the ancient craters Piazzi and Lagrange were swamped by so much debris that they are almost unrecognisable, two ellipses have been added to the image to show their size and shape. This image was taken on 25 May 2021 at 8:02 pm.

117: May 2026

This month we will look at a keyhole-shaped double crater called Torricelli.

This image was taken at 5:32 pm on 18 July 2018. The Sun was very low in the east.

The crater Torricelli is an unusual formation, in that it is composed of a 19 kilometre diameter cavity on the east, which is conjoined to a 8 kilometre diameter cavity on the western side. The floor is fairly uneven, with no hills or craterlets. The perimeter walls are fairly low all the way around, although at the western end there is no wall at all. In the image above, taken at sunrise on this part of the Moon, all the shadows are exaggerated. The shadows of the northern and southern walls stretch almost to the image's border, but there is no shadow of the western wall, showing that that there is no change in elevation there. A lunar rover travelling east towards Torricelli would find no change in slope until all at once it tumbled down into the 8 kilometre half of Torricelli. In this image, the centre of Torricelli is totally in shadow. The crater Torricelli lies in the northern half of an ancient ghost crater 87 kilometres in diameter, called Torricelli R. The area south of Torricelli is very rough, and covered with debris blasted out of the 101 kilometre crater Theophilus to the south (see item # 3 in the First Series of the Lunar Feature of the Month ).

Torricelli

In his old age, when he was blind, Galileo dictated his notes and letters to his loyal biographer and student, Vincenzo Viviani (1622-1703), who came to live with him at Arcetri as a 16-year-old in 1638. He was like a dutiful grandson to the aged Galileo. Viviani acted as an amanuensis (secretary, assistant and friend), and carefully wrote down all that Galileo dictated, and read his letters to him.

Viviani’s tutor at the University of Pisa, Evangelista Torricelli (1608-1647), also moved into Galileo’s house in his final months, to work in the company of the great man. The later successful careers of both Viviani (engineering and mathematics) and Torricelli (inventor of the mercury barometer) were greatly influenced by their conversations with Galileo. When Galileo died aged 77 on 8 January 1642, his positions with the Tuscan court and the University of Pisa both passed to Torricelli. When Torricelli died five years later, both positions went to Viviani. With Galileo’s death, the remaining Italian natural philosophers decided to maintain low profiles so as not to arouse the attention of the Inquisition. The Scientific Revolution that Galileo had begun therefore moved to northern Europe.

Most of our anecdotes about Galileo’s life come to us through Viviani’s biography 'Life of Galileo', a book still in print today, translated into English and available from Amazon.

118: June 2026

This month we will look at a rugged crater called Franklin.

The area shown above lies to the south-east of Endymion. The 13 kilometres crater Chevallier B lies 120 kilometres to the south-east of 27 kilometres crater Atlas P in # 2, and 100 kilometres east of the 88 kilometres walled plain Atlas in # 21 of the First Series of the Lunar Feature of the Month ). The image above includes the craters Hooke (36 kilometres), Berzelius (51 kilometres) and Messala A (26 kilometres), which may also be found in next month's image. This image was taken at 5:54 pm on 14 September 2018.

119: July 2026

This month we will look at a large, damaged walled plain called Messala.

The largest features in this image are the damaged walled plain Messala (124 kilometres) and the newer crater Geminus (86 kilometres). Messala had its floor swamped by up-welling magma soon after its creation, Since then, the flat floor has been struck by numerous impactors. Image taken at 5:51 pm on 14 September 2018.

With Geminus, the upwelling magma only filled the floor partially, and was insufficient to swamp the small cluster of mountains in its centre. This left Geminus much deeper than the other craters in the area, which allowed its interior walls to collapse down to the floor, causing great landslips and terraces around the circumference. These are particularly spectacular in this crater, although similar but smaller landslips can be seen in the craters Cepheus (40 kilometres) and Franklin (56 kilometres) in last month's image.

120: August 2026

This month we will look at a crater in the highlands north of Mare Crisium, called Macrobius.

The largest feature in this image is the walled plain Macrobius (65 kilometres) and the adjacent older crater Tisserand (36 kilometres). Macrobius had its floor swamped by up-welling magma soon after its creation, Since then, the flat floor has been struck by numerous impactors. Image taken at 6:14 pm on 14 September 2018.

Macrobius is a fairly recent impact crater with a diameter of 65 kilometres. Its walls are clearly defined with sharp crests and the flat floor has a small group of hills near its centre. A later impactor has struck squarely on Macrobius' south-west wall, leaving a 10 kilometre diameter depression called 'Macrobius C' there. The Lacus Bonitatus is a smallish flat lava plain to the north-west of Macrobius - its name means 'Lake of Goodness', and it is 70 kilometres from north to south, and 40 kilometres from east to west. The craters Hill (17 kilometres diameter) and Carmichael (20 kilometres diameter) are both Copernican, i.e. they are of the same age as the crater Copernicus, and occurred less than 1.1 billion years ago, up to the present day. Both are bowl-shaped and have high walls. The floors are covered with scree (rubble from the walls pooled on the floors). To their west is another lava plain called the Sinus Amoris (Bay of Love). It is 250 kilometres X 150 kilometres.

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

There are 100 features including 140 lunar images.

To access the First Series Archive, click here.

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