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Moon Craters

What to look for through the telescope

Recommended eyepiece: 26mm or 40mm

Craters Information

Craters were formed when pieces of rock struck the moon and left large holes.
The size of the typical crater visible on the moon is about 50 miles. The smallest craters that can be seen with the telescope are a few miles across. However, astronauts saw craters as small as a few inches across.
Over 500 thousand craters can be seen on the moon with the largest telescope on Earth.
If the area you have chosen has two craters which overlap, you may wish to ask which one was formed first and why.
If the crater you have chosen has a mountain peak or peaks in the center, you may wish to ask how the mountain peak got there. If you do ask, it is usually best to start by asking how craters are made and if that explanation is consistent with a mountain in the center. Of course, the mountain peak is formed when the material that originally flowed away from the impact site flows back in to fill up the hole. This is similar to dropping a pebble into a bucket of water.
The best times to look at cratered or highland areas on the moon are a few days before or after first and third quarter. Since sunlight strikes the moon's surface at a shallow angle it produces a lot of shadows which highlight the surface.
Often light colored material which appears to have been thrown out of the crater can be seen around the rim of the crater. This is indeed material that was ejected from the crater during its formation. These are called ray craters.
An interesting piece of information about the larger craters (more than 40 miles or so) is that if you were standing in the middle of them, you could not see the rim. It would be below your horizon.


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Furnerius


Longitude	58° E	Best Seen	3 to 16-day old moon
Latitude	36° N	Diameter	81 miles
Class		Depth	2.1 miles (11,000 feet)

Furnerius belongs to a subgroup of large craters called, mountain-walled plains. They are characterized by their shallow size, smooth floors, absence of a central mountain peak, and their polygonal (rather than circular or elliptical) outline. It appears that the crater was formed by dropping its floor rather than having their walls thrown up by some explosive action.
On the interior are craters, one with a central peak, ridges, and clefts. The most prominent cleft passes through the north wall. On the west, there is a gorge while in the south there is the crater Fraunhofer (33 miles across and 7900 feet deep).


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Langrenus


Longitude	61° E	Best Seen	3 to 16-day old moon
Latitude	09° S	Diameter	85 miles
Class	5	Depth	2.7 miles (14,256 feet)
		Central Mountain	3,200 feet

Langrenus Crater Information

Langrenus is a prominent circular impact crater, but it appears oblong due to foreshortening. It lies on the eastern shore of the Mare Fecunditatis.
The inner wall of Langrenus is wide and irregularly terraced, with an average width of about 20 kilometers. The walls of this crater are 6,500 feet above the surrounding plain.
Note the complex rides and craterlet-chains on the outer slopes.
The above craters are circular. They appear elliptical because they are near the edge of the moon and are therefore foreshortened.
Its ray system has been traced for 500 miles, but they are narrow and weak. Look for the crater Ansgarius just south of Langrenus.
The outer ramparts are irregular and hilly, and there is a bright, fragmented ray system spread across the maria to the west.
The interior of the crater reflects more light than the surroundings, so the crater stands out prominently when the sun is overhead.
The crater floor is covered by many boulders, and is slightly irregular in the northwest half. The central peaks rise about a kilometer above the floor, and a peak on the eastern rim ascends to an altitude of 3 km.

Namesake: Michel Florent van Langren (~1600 1675)

Dutch astronomer and cartographer

Michael van Langren was the youngest member of a family of Dutch cartographers and was born in Amsterdam, Netherlands.
His grandfather, Jacobus and his sons began producing both terrestrial as well as celestial globes in 1580.
Michael van Langren did not receive a university education however he did became a cartographer and engineer.
He served as the Royal Cosmographer and Mathematician to the King of Spain.
Among his contributions were attempts to determine longitude by observing the position of the Moon. This led him to make the first ever map of the Moon, and he produced maps of the Moon at thirty different phases.
He also assigned names to various lunar features, but few of these names were ever widely accepted because they were mostly related to the Spanish royal court. Ironically, the only lunar feature he named still bearing his designation is the crater he named after himself.
He made various maps of the Spanish Netherlands, and produced plans for a port near Dunkirk, improvements to the port of Ostend, efforts to clear the canals of Antwerp, flood control concepts, and fortifications.


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Petavious


Longitude	60° E	Best Seen	3 to 16-day old moon
Latitude	26° S	Diameter	99 by 110 miles
Class	5	Depth	2.6 miles (13,800 feet)
		Central Mountain	8,200 feet

Petavius Crater Information

Notice the cleft that runs from the central peak to the crater wall.
The outer wall of Petavius crater is unusually wide in proportion to the diameter, and displays a double rim along the south and west sides.
The height of the rim varies by as much as 50% from the lowest point, and a number of ridges radiate outward from the rim.
The convex crater floor has been resurfaced by lava flow, and displays a rille system named the Rimae Petavius.
The large central mountains are a prominent formation with multiple peaks, climbing 1.7 kilometers above the floor.
A deep fracture runs from the peaks toward the southwest rim of the crater.

Namesake: Denis Pétau aka: Dionysius Petavius (1583 - 1652)

French Jesuit theologian

Petau's claim to fame chiefly lies on his vast, but unfinished, De theologicis dogmatibus, the first systematic attempt ever made to treat the development of Christian doctrine from the historical point of view.


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Catharina


Longitude	24° E	Best Seen	5-day old moon
Latitude	18° S	Diameter	62 miles
Class		Depth	1.9 miles (10,000 feet)

Catharina Crater Information

Catharina is an ancient lunar impact crater located in the southern highlands.
It lies in a rugged stretch of land between the Rupes Altai scarp to the west and Mare Nectaris in the east.
With the large Cyrillus and Theophilus craters in the north, it forms a prominent grouping that is framed by the curve of the Rupes Altai. Together they form a notable feature when the sun is at a low angle to the surface.
The three craters Catharina, Cyrillus, and Theophilus represent three different epochs of the moon's history.
There is also a distinct difference in the ages of these three craters, with the age increasing significantly from north to south.
The rim of Catharina is heavily worn and irregular, with most of the north wall incised by the worn ring of crater Catharina P.
The northeast wall is deeply impacted by several smaller craters. No terracing remains on the inner wall, and the outer rampart has been nearly eroded away.
The floor is relatively flat but rugged, with a curved ridge formed by Catharina P, and the remains of a smaller crater near the south wall. Nothing remains of a central peak.

Namesake: Saint Catherine of Alexandria (287 - 305)

Christian saint and martyr

Saint Catherine is claimed to have been a noted scholar in the early 4th century. She was one of the saints to speak to Saint Joan of Arc.
The Orthodox Churches venerate her as a "great martyr," and in the Roman Catholic Church, she is traditionally revered as one of the Fourteen Holy Helpers.
Historians believe that Catherine ('the pure one') may not have existed and that she was more an ideal exemplary figure than an actual historical one.


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Cyrillus


Longitude	240° E	Best Seen	5-day old moon
Latitude	13° S	Diameter	62 miles
Class	3	Depth	2.2 miles (11,800 feet)

Cyrillus Crater Information

Cyrillus is a lunar impact crater located on the northwest edge of Mare Nectaris.
Intruding into the northeast rim is the equally large and younger Theophilus crater.
The crater walls are broken and dilapidated indicating that this crater is older than Theophilus. Cyrillus' central peak is also smaller and less conspicuous.
To the south is another prominent crater named Catharina. Together these three craters form a prominent trio in the southeast quadrant of the moon.
The crater Cyrillus is named after Saint Cyril of Alexandria, a 4th century Coptic Pope and theologian.
The floor of Cyrillus contains a reduced central hill and the considerable crater Cyrillus A. The walls of the broken formation of Cyrillus remain intact up until the point of junction with Theophilus.
Slightly northeast of its center, three rounded mountains rise to heights of 1,000 meters above the floor of Theophilus.

Namesake: Saint Cyril of Alexandria (378 - 444)

Saint Cyril was the Pope of Alexandria when the city was at its height of influence and power within the Roman Empire.
Cyril wrote extensively and was a leading protagonist in the Christological controversies of the 4th and 5th centuries.
He was a central figure in the First Council of Ephesus in 431 which led to the deposition of Nestorius as Archbishop of Constantinople.
Cyril is among the patristic fathers, and the Doctors of the Church, and his reputation within the Christian world has resulted in his titles "Pillar of Faith" and "Seal of all the Fathers".
The Eastern Orthodox Church celebrates his feast day on June 9 and also, together with St. Athanasius of Alexandria, on January 18.
The Roman Catholic Church did not commemorate him in the Tridentine Calendar.


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Theophilus


Longitude	27° E	Best Seen	5-day old moon
Latitude	11° S	Diameter	65 miles
Class		Depth	4.2 miles (22,300 feet)
		Central Mountain	6,500 feet

This crater has an unusually large multiple central mountain. The floor of this crater is not flat, but rather parabolic.


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Fracastorius


Longitude	33° E	Best Seen	5-day old moon
Latitude	21° S	Diameter	73 miles
Class	5 ?	Depth	3 miles (16,200 feet)
		Central Mountain	5,800 feet

Fracastorius Crater Information

Located just south of the Apollo 11 landing site.
Fracastorius is the lava flooded remnant of an ancient lunar impact crater located at the southern edge of Mare Nectaris. To the northwest of this formation lies the Beaumont crater, while to the northeast is Rosse.
Notice that its northern wall has disappeared under the molten lava of the mare that flooded its interior, leaving only mounds appearing in the lunar mare to mark the outline. This is a fine example of a ruined ring. On the floor are many objects, a circle of hills near the center, craterlets, and clefts. Of the latter, the most prominent lies on the south where it crosses the floor.
The lava that formed Mare Nectaris also invaded this crater, so the structure now forms a bay like extension.
The remainder of the rim is heavily worn and covered in lesser impact craters, leaving little of the original rim intact.
The maximum elevation of the rim is 2.4 km.
The Fracastorius crater has no central peak, but a long, slender rille runs across the middle of the floor in a generally east west direction.

Namesake: Girolamo Fracastoro (Fracastorius) (1478 - 1553)

Italian physician, mathematician, geographer, astronomer, poet and atomist.

Born of an ancient family in Verona, and educated at Padua where at 19 he was appointed professor at the University.
On account of his eminence in the practice of medicine, he was elected physician of the Council of Trent.
A bronze statue was erected in his honor by the citizens of Padua, while his native city commemorated their great compatriot by a marble statue.
He lived and practiced in his hometown.
In 1546 he proposed that epidemic diseases are caused by transferable tiny particles or "spores" that could transmit infection by direct or indirect contact or even without contact over long distances.
His theory remained influential for nearly three centuries, before being displaced by germ theory.
The name for syphilis is derived from Fracastoro's 1530 epic poem in three books, Syphilis sive morbus gallicus ("Syphilis or The French Disease"), about a shepherd named Syphilus. The poem suggests using mercury and "guaiaco" as a cure.
His 1546 book (De contagione "On Contagion") also gave the first description for typhus. The collected works of Fracastoro appeared for the first time in 1555.


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Picard


Longitude	55° E	Best Seen	4 to 16-day old moon
Latitude	15° S	Diameter	14 miles
Class		Depth	1.5 miles (8,000 feet)

Picard Crater Information

Picard Crater is a lunar impact crater that lies in the western part of the Mare Crisium.
It is the largest crater on the mare and is from the Eratosthenian period, which lasted from 3.2 to 1.1 billion years ago.
Inside Picard is a series of terraces that seismologists have attributed to a collapse of the crater floor.
The lowest point on the crater floor is approximately 2000 meters below its rim.
The crater rim of Picard is well-defined and shows little sign of wear, having a sharp-edged appearance. It has a small hill at the center.

Namesake: Jean-Felix Picard (1620-1682)

French Astronomer, priest and Geodesist

Jean-Felix Picard was not only a French astronomer but a priest as well, born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand.
As a geodesist, he was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted 1669-70. His measurements produced a result of 110.46 km for one degree of latitude, which gives a corresponding terrestrial radius of 6328.9 km. Today, the polar radius is measured at just over 6357 km. This was an error only 0.44% less than the modern value.
Picard made many improvements to the tools he used to make his measurements of one degree of the Earth’s latitude. This resulted in a much smaller margin of error than Tyco Brahe’s measurements. Picard’s measurements were 36 times more accurate.
Picard collaborated and corresponded with many scientists of his day, including Newton, Christian Huygens, Römer, Bartholin, Hudde, and even his main competitor, Giovanni Cassini.
These correspondences led to Picard's contributions to areas of science outside the area of geodesy, such as the aberration of light he observed while in Uraniborg, or his discovery of mercurial phosphorescence upon his observance of the faint glowing of a barometer. This discovery led to Newton's studies of spectrometry.
Picard also developed the system of right ascension for measuring positions of celestial objects.


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Aristotle

on map as Aristoteles


Longitude	18° E	Best Seen	7-day old moon
Latitude	50° N	Diameter	55 miles
Class		Depth	2.3 miles (12,000 feet)

Aristoteles Crater Information

Aristoteles crater is a lunar impact crater that lies near the southern edge of the Mare Frigoris, and to the east of the Montes Alpes mountain range. To the south of Aristoteles lies the slightly smaller crater Eudoxus, and these two form a distinctive pair for a telescope observer.
An arc of mountains between these craters bends to the west, before joining the walls. The smaller Mitchell crater is directly attached to the eastern rim of Aristoteles. To the west is the low, flooded Egede crater.
Observers have noted the crater wall of Aristoteles is slightly distorted into a rounded hexagon shape.
The inner walls are wide and finely terraced. The outer ramparts display a generally radial structure of hillocks through the extensive blanket of ejecta.
The crater floor is uneven, and covered in hilly ripples. Aristoteles does possess small central peaks and a row of hills and rocks radiate from the center, but they are somewhat offset to the south. The interior floor appears to have been filled with a layer of material, partially burying these projections.

Namesake: Aristotle (384 BC – 322 BC)

Greek philosopher

Aristotle was a Greek philosopher, a student of Plato and teacher of Alexander the Great.
He wrote on many different subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, politics, government, ethics, biology and zoology.
Aristotle (together with Socrates and Plato) is one of the most important philosophers in Western thought.
He was one of the first to systematize philosophy and science. His thinking on physics and science had a profound impact on medieval thought, which lasted until the Renaissance, and the accuracy of some of his biological observations was only confirmed in the last century.
His logical works contain the earliest formal study of logic known and were not superseded until the late nineteenth century.
In the Middle Ages, Aristotelian metaphysics had a profound influence on philosophical and theological thinking in the Islamic and Jewish traditions, and on Christian thought.
All aspects of Aristotle's philosophy continue to be the object of active academic study today.
Though Aristotle wrote many elegant treatises and dialogues, it is believed that the majority of his writings are now lost. His works have been lost and rediscovered several times, and it is believed that only about one fifth of the original works have survived.


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Eudoxus


Longitude	17° E	Best Seen	7-day old moon
Latitude	45° S	Diameter	40 by 43 miles
Class	1	Depth	2.7 miles (14,300 feet)

Eudoxus Crater Information

Eudoxus is a prominent lunar impact crater that lies to the east of the northern tip of the Montes Caucasus range.
It is located to the south of the prominent Aristoteles crater in the northern regions of the visible Moon.
To the south is the ruined formation of Alexander crater, and the small Lamèch crater lies to the southwest.
The rim of Eudoxus has a series of terraces on the interior wall, and slightly worn ramparts about the exterior.
Eudoxus and Aristotle are both noted for their massive walls.
It lacks a single central peak, but has a cluster of low hills about the mid point of the floor. The remainder of the interior floor is relatively level.
Notice the many hills on the interior, some of which are arranged in a ring. The southern part is very hilly. In the east, there are also many hills and mountains further east. One eastern mountain, 7,000 feet high, is cut through by a cleft.

Namesake: Eudoxus of Cnidus (410 or 408 BC – 355 or 347 BC)

Greek astronomer, mathematician, physician, scholar and student of Plato.
In mathematical astronomy his fame is due to the introduction of the astronomical globe, and his early contributions to understanding the movement of the planets.
His work on proportions shows tremendous insight into numbers; it allows rigorous treatment of continuous quantities and not just whole or rational numbers.
The work of Eudoxus and Archimedes as precursors of calculus was only exceeded in mathematical sophistication and rigour by Indian Mathematician Bhaskara and later by Newton.
Since all his own works are lost, our knowledge of him is obtained from secondary sources.
Eudoxus first travelled to Tarentum, Italy to study mathematics. While in Italy, Eudoxus visited Sicily where he studied medicine.
At the age of 23, he traveled to Athens to study with the followers of Socrates. He eventually became the pupil of Plato, with whom he studied for several months, but due to a disagreement they had a falling out.
Eudoxus was quite poor and could only afford an apartment at the Piraeus. To attend Plato's lectures, he walked the seven miles each direction, each day.
Due to his poverty, his friends raised funds sufficient to send him to Heliopolis, Egypt to pursue his study of astronomy and mathematics where he lived there 16 months.
Eudoxus eventually returned to his native Cnidus, where he served in the city assembly, built an observatory and continued writing and lecturing on theology, astronomy and meteorology.
An algebraic curve (the Kampyle of Eudoxus) is named after him.


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Hipparchus


Longitude	5° E	Best Seen	7-day old moon
Latitude	6° S	Diameter	93.2 miles
Class		Depth	2.1 miles (10,800 feet)

Hipparchus Crater Information

Hipparchus is the degraded remnant of a lunar crater; a vast ruined mountain-walled plain, 100 miles across, with the walls highest on the west. On the interior are partial rings, craterlets, shallow depressions on the east, and a cleft on the west.
It is located to the southeast of Sinus Medii, near the center of the visible Moon. To the south is the prominent Albategnius crater, and to the southwest lies Ptolemaeus crater, a feature of comparable dimensions to Hipparchus.
This feature is an ancient crater that has been subject to considerable modification due to subsequent impacts.
The western rim of Hipparchus has been all but worn away from impact erosion, and only low hills and rises on the surface remain to outline the feature. The wall to the east is somewhat more intact, but it too is heavily worn.
A pair of deep clefts lie in the western wall. These parallel a set of scars running through the south central highlands.
The crater floor has been partially resurfaced by basaltic lava flows. The southwest part of the floor, however, is slightly raised and much more rugged than the remainder. A few small rises and the raised partial rim of a flooded crater are all that remain of a central mountain mass.
Gaps in the northwest rim of Hipparchus crater rim form valleys that connect with the maria to the northwest.
Look for Horrocks, 17 by 19 miles, and 9,200 feet deep.
Also note the small crater Lyot on the floor.

Namesake: Hipparchus (190 BC – ca. 120 BC)

Greek astronomer, geographer, and mathematician of the Hellenistic period.
Hipparchus was born in Nicaea (now Iznik, Turkey), and probably died on the island of Rhodes.
He is known to have been a working astronomer from 147 BC to 127 BC. Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity.
He was the first Greek that made quantitative and accurate models for the motion of the Sun and Moon which survive to this day.
He possessed a trigonometric table, and appears to have solved some problems of spherical trigonometry.
It is thought that, with his solar and lunar theories and his trigonometric tables, he may have been the first to develop a reliable method to predict solar eclipses.
Some of his other achievements include the discovery of precession, the compilation of the first comprehensive star catalog of the western world, and possibly the invention of the astrolabe.
It would be three centuries before Claudius Ptolemaeus' synthesis of astronomy would supersede the work of Hipparchus.


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Walther


Longitude	0° E	Best Seen	7-day old moon
Latitude	33° S	Diameter	78 by 88 miles
Class	4	Depth	2.3 miles (12,000 feet)

Walther Crater Information

Walther is aa mountain-walled plain, ancient lunar impact crater located in the southern highland region of the Moon.
It is joined along the western rim to the Deslandres crater. To the northeast is Aliacensis crater, and joined to the southeast rim is the irregular Nonius crater.
The rim of Walther crater is complex, heavily eroded and incised by lesser impacts.
The wall retains a generally circular form, but many of its features have been worn away and there is a slight protruding bulge in the western rim.
The floor has been resurfaced after the original impact, leaving the southwest half relatively smooth.
In the northwest quadrant is an offset central peak that has been worn and impacted by several small craters.

Namesake: Bernhard Walther (1430 - 1504)

German merchant, humanist and astronomer.

As a merchant, Walther became a man of means, devoting much of it to scientific pursuits in the area of astronomy.
When Johann Muller Regiomontanus settled in Nuremberg in 1471, they worked in collaboration to build an observatory and a printing press.
After the death of Regiomontanus in 1476 in Rome, Walther bought his instruments and continued the observation of planets till his death. His house is now a museum.


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Werner


Longitude	3° E	Best Seen	7-day old moon
Latitude	28° S	Diameter	43 miles
Class	1	Depth	2.8 miles (15,000 feet)

Werner Crater Information

Werner is a prominent lunar impact crater that lies in the rugged south central highlands of the Moon. It is almost joined with Aliacensis crater to the southeast, and the pair form a rugged valley in the intervening gap.
Due west of Werner is the distorted Regiomontanus crater, and to the north is the remains of the Blanchinus crater. It is from the Eratosthenian period, which lasted from 3.2 to 1.1 billion years ago.
The rim of Werner crater shows little appearance of wear and is one of the most circular of all lunar craters. It is much younger and less eroded than the other surrounding large craters.
The interior wall is terraced, and there is a noticeable wall or ridge on the exterior.
There are several low rises on the crater floor and a notable central peak.
Its highly terraced walls attain peaks of almost 1,500 feet. The crater is 45 miles (70 kilometers) in diameter, and the difference in height between its rim and its deepest parts is 4.2 kilometers.

Namesake: Johann(es) Werner (1468 – 1522)

German parish priest in Nuremberg, mathematician, astronomer, geographer and skilled instrument maker.

His mathematical works were in the areas of spherical trigonometry, as well as conic sections.
This work further developed the suggestion of Regiomontanus that the occurrences of eclipses and the orbits of comets could be used to find longitude. This approach did not work out because the instruments being used were not accurate enough.
In the area of geography, Werner is best known for his work in translating Ptolemy’s work, Geographia in 1514.
He refined and promoted the Werner map projection, a cordiform (heart shape) projection map that had been developed by Johannes Stabius (Stab) of Vienna around 1500.
After its introduction by Werner in his 1514 book, the Werner projection was commonly used for world maps and some continental maps through the 16th century and into the 17th century.
By the 18th century, it was replaced by the Bonne projection for continental maps. The Werner projection is only used today for instructional purposes and as a novelty.
In the area of Meteorology, many consider Werner as a pioneer of modern meteorology and weather forecasting. Between 1513 and 1520, Johann Werner made the first regular observations of the weather conditions in Germany.


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Archimedes


Longitude	4° W	Best Seen	9-day old moon
Latitude	30° N	Diameter	51 miles
Class	5	Depth	1.3 miles (6,800 feet)

Archimedes Crater Information

Archimedes Crater is a large lunar impact crater on the eastern edges of the Mare Imbrium.
East of Archimedes is the Autolycus crater, and the stretch of lunar surface between these two formations was the crash landing site of the Luna 2 landing craft. This was the first robotic craft to reach the surface of the moon, landing September 13, 1959.
To the northwest is the prominent Aristillus crater. The lava plain between Archimedes, Aristillus, and Autolycus forms the Sinus Lunicus bay of Mare Imbrium.
A wrinkle ridge leads away from Archimedes toward the north northwest, crossing this maria.
The diameter of Archimedes is the largest of any crater on the Mare Imbrium. The rim has a significant outer rampart brightened with ejecta and the upper portion of a terraced inner wall, but lacks the ray system associated with younger craters.
A triangular promontory extends 30 kilometers from the southeast of the rim.
The interior of the crater lacks a central peak, and is flooded with maria. It is devoid of significant raised features, although there are a few tiny meteor craters near the rim.
The lava floor is similar to that of Plato but much lighter and smoother.

Namesake: Archimedes of Syracuse (287 BC – 212 BC)

Greek mathematician, physicist, engineer, inventor, and astronomer.

Archimedes is regarded as one of the leading scientists in classical antiquity.
Among his advances in physics are the foundations of hydrostatics and the explanation of the principle of the lever.
He is credited with designing innovative machines, including siege engines and the screw pump that bears his name.
Archimedes is also considered to be one of the greatest mathematicians of all time.
He used the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of Pi.
He also defined the spiral bearing his name, formulas for the volumes of surfaces of revolution and an ingenious system for expressing very large numbers.
Archimedes died during the Siege of Syracuse when he was killed by a Roman soldier despite orders that he should not be harmed.
Cicero describes visiting the tomb of Archimedes, which was surmounted by a sphere inscribed within a cylinder. Archimedes had proved that the sphere has two thirds of the volume and surface area of the cylinder (including the bases of the latter), and regarded this as the greatest of his mathematical achievements.


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Plato


Longitude	10° W	Best Seen	9-day old moon
Latitude	52° N	Diameter	64 by 67 miles
Class	5	Depth	1.5 miles (8,000 feet)

This is a mountain-walled plain. It shows up rather well during full moon.

Plato Crater Information

Plato is the maria surfaced remains of a lunar impact crater.
It is located on the northeastern shore of the Mare Imbrium, at the western extremity of the Montes Alpes mountainous range.
The age of the Plato walled plain is about 3.84 billion years; younger than Mare Imbrium to the south.
The rim is irregular with jagged peaks that project prominent shadows across the crater floor when the sun is at a low angle.
Sections of the inner wall display signs of past slumping, most notably a large triangular slide along the western side.
The rim of Plato is circular, but from the Earth it appears oval due to foreshortening.
The flat floor of Plato crater has a relatively low albedo, making it appear dark in comparison to the surrounding rugged terrain.
The floor is free of significant impact craters and lacks a central peak. However there are a few small craterlets scattered across the floor.
The astronomer Johannes Hevelius originally called this feature the 'Greater Black Lake'.

Namesake: Plato (424 – 348)

Classical Greek philosopher and mathematician.

Together with his teacher, Socrates, and his student, Aristotle, Plato helped to lay the philosophical foundations of Western culture.
Plato was the founder of the Academy in Athens, the first institution of higher learning in the western world.
Plato was originally a student of Socrates, and was as much influenced by his thinking as by what he saw as his teacher's unjust death.
Plato's brilliance as a writer and thinker can be witnessed by reading his Socratic dialogues.
Interestingly, although there is little question that Plato lectured at the Academy that he founded, the pedagogical function of his dialogues, if any, is not known with any degree of certainty.
Plato’s dialogues have been used to teach a range of subjects, primarily philosophy, logic, rhetoric, and mathematics.


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Aliacensis


Longitude	50° E	Best Seen	9-day old moon
Latitude	31° S	Diameter	46 by 55 miles
Class	1	Depth	2.4 miles (12,900 feet)

Aliacensis Crater Information

Contrast the walls of this crater with the circular walls of Werner.


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Alphonsus


Longitude	30° W	Best Seen	9-day old moon
Latitude	14° S	Diameter	64 by 73 miles
Class	5	Depth	1.25 miles (6,600 feet)

Alphonsus Crater Information

Look for craterlets and park spots on the interior. On November 3, 1958, a Russian astronomer thought that he observed a volcanic eruption near the central peak. If this was anything, it was probably outgassing.


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Arzachel


Longitude	20° W	Best Seen	9-day old moon
Latitude	19° S	Diameter	59 miles
Class	3	Depth	2.5 miles (13,000 feet)

Arzachel Crater Information

This crater has massive terraced walls 10 miles thick. Also look for the central mountain which is about 5 miles southwest of the crater's center.


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Clavius


Longitude	15° W	Best Seen	9-day old moon
Latitude	59° S	Diameter	132 by 152 miles
Class	5	Depth	3 miles (16,100 feet)
		Walls	5,400 feet high and
			35 miles thick at base

Clavius Crater Information

Note the string of craters on the floor. Clavius is the second largest crater on the moon; only Deslandres is larger.
On the north and south walls are deep craters, one Porter, and the other Rutherford.
In addition to the principal crater-chain, the floor also contains numerous small craters, hills, and some ridges but no clefts are seen.
Its walls slope downward for 15 miles.


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Clavius B


Longitude	15° W	Best Seen	9-day old moon
Latitude	59° S	Diameter	30 miles
Class	1	Depth	1.9 miles (10,200 feet)

Clavius B Crater Information

-- none --


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Copernicus


Longitude	20° W	Best Seen	9-day old moon
Latitude	10° N	Diameter	60 miles
Class	1	Depth	2.4 miles (12,600 feet)
		Walls	14 miles thick

Copernicus Crater Information

Copernicus is a prominent lunar impact crater located in eastern Oceanus Procellarum. Notice the central peak with three distinct peaks. Also notice the ray system.
The crater Copernicus is estimated to be about 800 million years old, and typifies craters that formed during the Copernican period in that it has a prominent ray system.
Copernicus is visible using binoculars, and is located slightly northwest of the center of the Moon's Earth facing hemisphere.
Due to its relative youth, the crater has remained in a relatively pristine shape since it formed.
The circular rim has a discernible hexagonal form, with a terraced inner wall and a 30 km wide, sloping rampart that descends nearly a kilometer to the surrounding maria.
There are three distinct terraces visible, and arc shaped landslides due to slumping of the inner wall as the crater debris subsided.
The crater rays spread as far as 800 kilometers across the surrounding maria, overlaying rays from the Aristarchus and Kepler craters. The rays are less distinct than the long, linear rays around Tycho crater, instead forming a nebulous pattern with plumy markings.

Namesake: Nicolaus Copernicus (1473 - 1543)

Astronomer, physician, classical scholar, translator, Catholic cleric, jurist, governor, military leader, diplomat and economist.

Copernicus was the first astronomer to formulate a scientifically based heliocentric cosmology that displaced the Earth from the center of the universe.
His epochal book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), is often regarded as the starting point of modern astronomy and the defining epiphany that began the Scientific Revolution.
Although Greek, Indian and Muslim individuals published heliocentric hypotheses centuries before Copernicus, his publication of a scientific theory of heliocentrism, demonstrating that the motions of celestial objects can be explained without putting the Earth at rest in the center of the universe,
Copernicus’ book stimulated further scientific investigations, and became a landmark in the history of modern science that is known as the Copernican Revolution.
Amid his extensive responsibilities, astronomy figured as little more than an avocation — yet it was in that field that he made his mark upon the world.


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Erathosthenes


Longitude	11° W	Best Seen	9-day old moon
Latitude	15° N	Diameter	37 miles
Class	1	Depth	2.3 miles (12,300 feet)

Erathosthenes Crater Information

Look for the tail-like mountain ridge that extends for about 50 miles to the southwest.


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Ptolemy

Listed on the map as Ptolomaeus


Longitude	02° W	Best Seen	9-day old moon
Latitude	09° S	Diameter	93 miles
Class	5	Depth	1.9 miles (9,800 feet)
		Walls	1.6 miles (8,200 feet)

Ptolemy Crater Information

The interior of the mountain-walled plain has been filled with lava to approximately the outside level. Look for the crater Ammonius1, six miles across and 3,900 feet deep, northeast of center.
This is a great walled plain. On the surface, which is very dark at sunrise, are over 200 objects including craterlets, shallow depressions, ridges, and a cleft on the east. The highest peak on the walls rises 9,000 feet.
Note that someone standing near the center would not see the mountainous border since it would be below the horizon. The horizon would be about 2 miles from you.
In the past this crater was identified as Ptolemaeus A, before being renamed by the IAU in 1976. (source: https://planetarynames.wr.usgs.gov/Feature/236)


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Tycho


Longitude	11° W	Best Seen	9 to 15-day old moon
Latitude	43° S	Diameter	56 miles
Class	1	Depth	2.6 miles (13,800 feet)
		Walls	over 3 miles
			(17,000 feet) above
			crater floor
		Central Mountain	0.9 miles (4,800 feet)

Tycho Crater Information

Tycho is a prominent lunar impact crater located in the southern lunar highlands, named after Tycho Brahe and is one of the youngest craters on the moon. Its walls are 13 miles thick.
Note the extensive ray system (especially during full moon). Some of the rays are more than 1,000 miles long.
The surface around Tycho has numerous craters of various differing radii, many overlapping older craters. Some of the smaller craters are secondary craters formed from larger chunks of ejecta from Tycho. To the south is Street crater; to the east Pictet, and to the north northeast is Sasserides crater.
Tycho is a (relatively) very young crater, with an estimated age of 108 million years, based on analysis of samples of the crater rays recovered during the Apollo 17 mission.
This age suggests that the impactor may have been a member of the Baptistina family of asteroids, but as the composition of the impactor is unknown this is currently conjecture.
It is also speculated that a larger asteroid from the same family may have been the impactor responsible for creating Chicxulub Crater on Earth 65 million years ago, causing the extinction of the dinosaurs.
The crater is sharply defined and free of the wear that affects older craters. The interior has a high albedo that is prominent when the sun is overhead, and the crater is surrounded by a distinctive ray system forming long spokes that reach as far away as 1,500 kilometers.
The walls beyond the rim have a lower albedo than the interior for a distance of over a hundred kilometers, and are free of the ray markings that lie beyond. This darker rim may have been formed from minerals excavated during the impact.
Its inner wall is slumped and terraced, sloping down to a rough but nearly flat floor exhibiting small, knobby domes. The floor displays signs of past volcanism, most likely from rock melt caused by the impact.
Detailed photographs of the floor show that it is covered in a criss crossing array of cracks and small hills. The central peaks rise 1.6 kilometers above the floor, and a lesser peak stands just to the northeast of the primary massif.
Infrared observations of the lunar surface during an eclipse have demonstrated that Tycho cools at a slower rate than other parts of the surface, making the crater a "hot spot". This effect is caused by the difference in materials that cover the crater.

Namesake: Tycho Brahe (December 14, 1546 – October 24, 1601)

Danish nobleman, astronomer, astrologer and alchemist.

Tycho Brahe was granted an estate on the island of Hven and the funding to build the Uraniborg, an early research institute, where he built large astronomical instruments and took many careful measurements of the heavens.
As an astronomer, Tycho worked to combine the geometrical benefits of the Copernican system with the philosophical benefits of the Ptolemaic system into his own model of the universe, the Tychonic system.
From 1600 until his death in 1601, he was assisted by Johannes Kepler, who would later use Tycho's astronomical information to develop his own theories of astronomy.
He is credited with the most accurate astronomical observations of his time, and the data were used by his assistant Kepler to derive the laws of planetary motion.
No one before Tycho had attempted to make so many redundant observations. In addition, the mathematical tools to take advantage of these careful observations had not yet been developed.
He did what others before him were unable or unwilling to do — to catalogue the planets and stars with enough accuracy so as to determine whether the Ptolemaic or Copernican system was more valid in describing the heavens.


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Aristarchus


Longitude	47° W	Best Seen	11-day old moon
Latitude	24° N	Diameter	25 miles
Class	1	Depth	2.3 miles (11,900 feet)

Aristarchus Crater Information

Aristarchus is a prominent lunar impact crater that lies in the northwest part of the Moon's near side. Look for bands running from the peak to the eastern wall soon after sunrise.
It is considered the brightest of the large formations on the lunar surface, with an albedo nearly double that of most lunar features.
The feature is bright enough to be visible to the naked eye, and is dazzling in a large telescope. It is also readily identified when most of the lunar surface is illuminated.
The crater is located at the southeastern edge of the Aristarchus plateau, an elevated area that contains a number of volcanic features, such as sinuous rilles.
Aristarchus was originally named after the Greek astronomer Aristarchus of Samos by the Italian map maker Giovanni Riccioli. He gave the spot shaped telescopic features (later called craters) eponyms of noted astronomers and philosophers. Although widely adopted, the name only became an official international standard by a vote of the IAU General Assembly in 1935.

Namesake: Aristarchus (310 BC - 230 BC)

Greek astronomer and mathematician,

Aristarchus was born on the island of Samos, in Greece.
He was the first person to present an explicit argument for a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus").
He both identified the central fire with the Sun, as well as putting other planets in correct order from the Sun.
His astronomical ideas were rejected in favor of the geocentric theories of Aristotle and Ptolemy until they were successfully revived by Copernicus and extensively developed and built upon by Kepler and Isaac Newton nearly 2000 years later.


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Gassendi


Longitude	40° W	Best Seen	11-day old moon
Latitude	17° S	Diameter	70 miles
Class	5	Depth	1.2 miles (6,600 feet)
		Walls	1.7 miles (3,200 feet)
		Central Peak	3,920 feet

Gassendi Crater Information

On the interior is a central mountain group, 4,000 feet high which is the remains of an inner ring. Craterlets, ridges, and a fine system of clefts can also be seen.
Look for Gassendi A (20 by 24 miles, 8500 feet deep) on the north wall. On the south, the crater's walls have been melted down to hills for a 30 mile stretch.


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Schiller


Longitude	40° W	Best Seen	11-day old moon
Latitude	52° S	Diameter	48 by 113 miles
Class	3	Depth	2.4 miles (15,500 feet)

Schiller Crater Information

Schiller is an oddly shaped impact crater bearing a slight resemblance to a footprint left by a shoe. The rim is elongated and may be a fusion of 2 or more craters.
There is a linear ridge formation dividing the northwest end of the crater floor.
At the southwestern end of the crater is a narrow valley connecting to another smaller crater.


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Kepler


Longitude	38° W	Best Seen	11-day old moon
Latitude	8° N	Diameter	20 miles
Class		Depth	1.6 miles (8,500 feet)

Kepler Crater Information

Kepler is a young lunar impact crater that lies between the Oceanus Procellarum to the west and Mare Insularum in the east. To the southeast is the Encke crater.
Kepler is most notable for the prominent ray system that covers the surrounding maria. The rays extend for well over 300 kilometers, overlapping the rays from other craters.
Kepler has a small rampart of ejecta surrounding the exterior of its high rim. The outer wall is not quite circular, and possesses a slightly polygonal form.
The interior walls of Kepler are slumped and slightly terraced, descending to an uneven floor and a minor central rise.
One of the rays from Tycho crater, when extended across the Oceanus Procellarum, intersects Kepler crater. This was a factor in the choice of the crater's name when Giovanni Riccioli was creating his system of lunar nomenclature, as Kepler used the observations of Tycho Brahe while devising his three laws of planetary motion.

Namesake: Johannes Kepler (1571 – 1630)

German mathematician, astronomer and astrologer, and a key figure in the 17th century astronomical revolution.

He is best known for his laws of planetary motion, codified by later astronomers based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican Astronomy.
Before Kepler, planets' paths were computed by combinations of the circular motions of the celestial orbs. After Kepler, astronomers gradually shifted their attention from orbs to orbits — paths that could be represented mathematically as an ellipse.
Kepler's laws also provided one of the foundations for Isaac Newton's theory of universal gravitation.
During his career, Kepler was a mathematics teacher at a seminary school in Graz, Austria, an assistant to astronomer Tycho Brahe, the court mathematician to Emperor Rudolf II, a mathematics teacher in Linz, Austria, and an adviser to General Wallenstein.
He also did fundamental work in the field of optics, invented an improved version of the refracting telescope, and helped to legitimize the telescopic discoveries of his contemporary Galileo Galilei.
Kepler lived in an era when there was no clear distinction between astronomy and astrology, but there was a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of the more prestigious discipline of natural philosophy).
Kepler also incorporated religious arguments and reasoning into his work, motivated by the religious conviction that God had created the world according to an intelligible plan that is accessible through the natural light of reason.


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Grimaldi


Longitude	68° W	Best Seen	13 to 15-day old moon
Latitude	6° S	Diameter	140 by 145 miles
Class	5	Depth	2 miles (10,500 feet)

Grimaldi Crater Information

Grimaldi is a large basin located near the western limb of the Moon. Look for the dark ellipse which marks the heavily stained floor.
Note the low mountain ring and dark floor. (Darker than Plato.) Grimaldi may be the connecting link between the maria and the mountain-walled plains.
It lies to the southwest of the Oceanus Procellarum, and southeast of Riccioli crater. Between Oceanus Procellarum is the Damoiseau crater, and to the north is Lohrmann crater.
The inner wall of Grimaldi has been so heavily worn and eroded by subsequent impacts that it forms a low, irregular ring of hills, ridges and peaks, rather than a typical crater rim. However, there are peaks remaining that reach heights of over 2 kilometers.
The floor is the most notable feature of this crater, forming a flat, relatively smooth and featureless surface with a particularly low albedo.
The dark shade of the floor contrasts with the brighter surroundings, making the crater easy to locate.
The approximate diameter of the inner rim is 140 kilometers. Beyond the basin are the scattered remnants of an outer wall, which has a diameter of 220 kilometers.
This exterior rim is more intact to the north and west of the crater than elsewhere.

Namesake: Francesco Maria Grimaldi (1618 - 1663)

Italian mathematician and physicist

Between 1640 and 1650, working with Riccioli, he investigated the free fall of objects, confirming that the distance of fall was proportional to the square of the time taken.
In astronomy, he built and used instruments to measure geological features on the Moon, and drew an accurate map or selenograph which was published by Riccioli.
He was the first to make accurate observations on the diffraction of light (although by some accounts Leonardo da Vinci had earlier noted it), and coined the word 'diffraction'.
Later physicists used his work as evidence that light was a wave, and Isaac Newton used it to arrive at his more comprehensive theory of light.


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Hevelius


Longitude	65° W	Best Seen	13-day old moon
Latitude	1° N	Diameter	66 by 69 miles
Class	5	Depth	1.3 miles (7,000 feet)

Hevelius Crater Information

Try to find the low mountain or hill just north of center. It is often hard to distinguish it from the floor.
Look for Cavalerius 37 miles in diameter and 2 miles (10,800 feet) deep on the north wall.


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Pythagoras

MOUNTAIN-WALLED PLAIN


Longitude	66° W	Best Seen	13-day old moon
Latitude	64° N	Diameter	81 by 90 miles
Class	1	Depth	3.1 miles (16,400 feet)

Pythagoras Crater Information

-- none --


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