The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, including data obtained during the Clementine mission. The most visible topographic feature is the giant far side South Pole-Aitken basin, which possesses the lowest elevations of the Moon. The highest elevations are found just to the north-east of this basin, and it has been suggested that this area might represent thick ejecta deposits that were emplaced during an oblique South Pole-Aitken basin impact event. Other large impact basins, such as the maria Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims.
Another distinguishing feature of the Moon's shape is that the elevations are on average about 1.9 km higher on the far side than the near side. If it is assumed that the crust is in isostatic equilibrium, and that the density of the crust is everywhere the same, then the higher elevations would be associated with a thicker crust. Using gravity, topography and seismic data, the crust is thought to be on average about 50 ± 15 km thick, with the far-side crust being on average thicker than the near side by about 15 km. [ obsolete source ]
Selenography is the study of the surface and physical features of the Moon. Historically, the principal concern of selenographists was the mapping and naming of the lunar maria, craters, mountain ranges, and other various features. This task was largely finished when high resolution images of the near and far sides of the Moon were obtained by orbiting spacecraft during the early space era. Nevertheless, some regions of the Moon remain poorly imaged (especially near the poles) and the exact locations of many features (like crater depths) are uncertain by several kilometers. Today, selenography is considered to be a subdiscipline of selenology, which itself is most often referred to as simply "lunar science." The word selenography is derived from the Greek lunar deity Σελήνη Selene and γράφω graphō, "I write".
The idea that the Moon is not perfectly smooth originates to at least c. 450 BC, when Democritus asserted that the Moon's "lofty mountains and hollow valleys" were the cause of its markings. However, not until the end of the 15th century AD did serious study of selenography begin. Around AD 1603, William Gilbert made the first lunar drawing based on naked-eye observation. Others soon followed, and when the telescope was invented, initial drawings of poor accuracy were made, but soon thereafter improved in tandem with optics. In the early 18th century, the librations of the Moon were measured, which revealed that more than half of the lunar surface was visible to observers on Earth. In 1750, Johann Meyer produced the first reliable set of lunar coordinates that permitted astronomers to locate lunar features. [ citation needed ]
Lunar mapping became systematic in 1779 when Johann Schröter began meticulous observation and measurement of lunar topography. In 1834 Johann Heinrich von Mädler published the first large cartograph (map) of the Moon, comprising 4 sheets in size, and he subsequently published The Universal Selenography.All lunar measurement was based on direct observation until March 1840, when J.W. Draper, using a 5 inch reflector, produced a daguerreotype of the Moon and thus introduced photography to astronomy. At first, the images were of very poor quality, but as with the telescope 200 years earlier, their quality rapidly improved. By 1890 lunar photography had become a recognized subdiscipline of astronomy.
The 20th century witnessed more advances in selenography. In 1959, the Soviet spacecraft Luna 3 transmitted the first photographs of the far side of the Moon, giving the first view of it in history. The United States of America launched the Ranger spacecraft between 1961 and 1965 to photograph the lunar surface until the instant they impacted it, the Lunar Orbiters between 1966 and 1967 to photograph the Moon from orbit, and the Surveyors between 1966 and 1968 to photograph and softly land on the lunar surface. The Soviet Lunokhods 1 (1970) and 2 (1973) traversed almost 50 km of the lunar surface, making detailed photographs of the lunar surface. The Clementine spacecraft obtained the first nearly global cartograph (map) of the lunar topography, and also multispectral images. Successive missions transmitted photographs of increasing resolution.
The oldest known illustration of the Moon was found in a passage grave in Knowth, County Meath, Ireland. The tomb was carbon dated to 3330–2790 BC.Leonardo da Vinci made and annotated some sketches of the Moon in c. 1500. William Gilbert made a drawing of the Moon in which he denominated a dozen surface features in the late 16th century; it was published posthumously In De Mondo Nostro Sublunari Philosophia Nova. After the invention of the telescope, Thomas Harriot (1609), Galileo Galilei (1609), and Charles Scheiner (1614) made drawings also.
Michiel Florent van Langren was an early-modern pioneer in the history of lunar cartography and selenography.The first serious denominations of the surface features of the Moon, based on telescopic observation, were made by Van Langren in 1645. His work is considered the first true cartograph (map) of the Moon because it demarcated the various lunar maria, craters, and mountains and ranges. Many of his denominations were distinctly Catholic, denominating craters in honor of Catholic royalty and capes and promontories in honor of Catholic saints. The lunar maria were denominated in Latin for terrestrial seas and oceans. Minor craters were denominated in honor of astronomers, mathematicians, and other famous scholars.
In 1647, Johannes Hevelius produced the rival work Selenographia , which was the first lunar atlas. Hevelius ignored the nomenclature of Van Langren and instead denominated the lunar topography according to terrestrial features, such that the names of lunar features corresponded to the toponyms of their geographical terrestrial counterparts, especially as the latter were denominated by the ancient Roman and Greek civilizations. This work of Hevelius influenced his contemporary European astronomers, and the Selenographia was the standard reference on selenography for over a century.
Giambattista Riccioli, SJ, a Catholic priest and scholar who lived in northern Italy authored the present scheme of Latin lunar nomenclature. His Almagestum novum was published in 1651 as summary of then current astronomical thinking and recent developments. In particular he outlined the arguments in favor of and against various cosmological models, both heliocentric and geocentric. Almagestum Novum contained scientific reference matter based on contemporary knowledge, and contemporary educators across Europe widely used it. Although this handbook of astronomy has long since been superseded, its system of lunar nomenclature is used even today.
The lunar illustrations in the Almagestum novum were drawn by a fellow Jesuit educator named Francesco Grimaldi, SJ. The nomenclature was based on a subdivision of the visible lunar surface into octants that were numbered in Roman style from I to VIII. Octant I referenced the northwest section and subsequent octants proceeded clockwise in alignment with compass directions. Thus Octant VI was to the south and included Clavius and Tycho Craters.
The Latin nomenclature had 2 components: the first denominated the broad features of terrae (lands) and maria (seas) and the second denominated the craters. Riccioli authored lunar toponyms derived from the names of various conditions, including climactic ones, whose causes were historically attributed to the Moon. Thus there were the seas of crises ("Mare Crisium"), serenity ("Mare Serenitatis"), and fertility ("Mare Fecunditatis"). There were also the seas of rain ("Mare Imbrium"), clouds ("Mare Nubium"), and cold ("Mare Frigoris"). The topographical features between the maria were comparably denominated, but were opposite the toponyms of the maria. Thus there were the lands of sterility ("Terra Sterilitatis"), heat ("Terra Caloris"), and life ("Terra Vitae"). However, these names for the highland regions were supplanted on later cartographs (maps). See List of features on the Moon#Terra for a complete list.
Many of the craters were denominated topically pursuant to the octant in which they were located. Craters in Octants I, II, and III were primarily denominated based on names from ancient Greece, such as Plato, Atlas, and Archimedes. Toward the middle in Octants IV, V, and VI craters were denominated based on names from the ancient Roman Empire, such as Julius Caesar, Tacitus, and Taruntius. Toward the southern half of the lunar cartograph (map) craters were denominated in honor of scholars, writers, and philosophers of medieval Europe and Arabic regions. The outer extremes of Octants V, VI, and VII, and all of Octant VIII were denominated in honor of contemporaries of Giambattista Riccioli. Features of Octant VIII were also denominated in honor of Copernicus, Kepler, and Galileo. These persons were "banished" to it far from the "ancients", as a gesture to the Catholic Church.[ citation needed ] Many craters around the Mare Nectaris were denominated in honor of Catholic saints pursuant to the nomenclature of Van Langren. All of them were, however, connected in some mode with astronomy. Later cartographs (maps) removed the "St." from their toponyms.
The lunar nomenclature of Giambattista Riccioli was widely used after the publication of his Almagestum Novum, and many of its toponyms are presently used. The system was scientifically inclusive and was considered eloquent and poetic in style, and therefore it appealed widely to his contemporaries. It was also readily extensible with new toponyms for additional features. Thus it replaced the nomenclature of Van Langren and Hevelius.
Later astronomers and lunar cartographers augmented the nomenclature with additional toponyms. The most notable among these contributors was Johann H. Schröter, who published a very detailed cartograph (map) of the Moon in 1791 titled the Selenotopografisches Fragmenten. Schröter's adoption of Riccioli's nomenclature perpetuated it as the universally standard lunar nomenclature. A vote of the International Astronomical Union (IAU) in 1935 established the lunar nomenclature of Riccioli, which included 600 lunar toponyms, as universally official and doctrinal.
The IAU later expanded and updated the lunar nomenclature in the 1960s, but new toponyms were limited to toponyms honoring deceased scientists. After Soviet spacecraft photographed the far side of the Moon, many of the newly discovered features were denominated in honor of Soviet scientists and engineers. The IAU assigned all subsequent new lunar toponyms. Some craters were denominated in honor of space explorers.
Johann H. Mädler authored the nomenclature for satellite craters. The subsidiary craters surrounding a major crater were identified by a letter. These subsidiary craters were usually smaller than the crater with which they were associated, with some exceptions. The craters could be assigned letters "A" through "Z", with "I" omitted. Because the great majority of the toponyms of craters were masculine, the major craters were generically denominated "patronymic" craters.
The assignment of the letters to satellite craters was originally somewhat haphazard. Letters were typically assigned to craters in by order of significance rather than location. Precedence depended on the angle of illumination from the Sun at the time of the telescopic observation, which could change during the lunar day. In many cases the assignments were seemingly random. In a number of cases the satellite crater was located closer to a major crater with which it was not associated. To identify the patronymic crater, Mädler placed the identifying letter to the side of the midpoint of the feature that was closest to the associated major crater. This also had the advantage of permitting omission of the toponyms of the major craters from the cartographs (maps) when their subsidiary features were labelled.
Over time, lunar observers assigned many of the satellite craters an eponym. The International Astronomical Union (IAU) assumed authority to denominate lunar features in 1919. The commission for denominating these features formally adopted the convention of using capital Roman letters to identify craters and valleys.
When suitable cartographs (maps) of the far side of the Moon became available by 1966, Ewen A. Whitaker denominated satellite features based on the angle of their location relative to the major crater with which they were associated. A satellite crater located due north of the major crater was identified as "Z". The full 360° circle around the major crater was then subdivided evenly into 24 parts, like a 24-hour clock. Each "hour" angle, running clockwise, was assigned a letter, beginning with "A" at 1 o'clock. The letters "I" and "O" were omitted, resulting in only 24 letters. Thus a crater due south of its major crater was identified as "M".
The Moon obviously lacks any sea level. The USGS's Lunar Orbiter Laser Altimeter (LOLA), an instrument on NASA’s Lunar Reconnaissance Orbiter (LRO), employs a digital elevation model (DEM) that uses the lunar reference radius of 1,737.4 km (1,079.6 mi).
The following is a list of historically-notable lunar maps and atlases, arranged in chronological order by publication date.
Tycho is a prominent lunar impact crater located in the southern lunar highlands, named after the Danish astronomer Tycho Brahe (1546–1601). It is estimated to be 108 million years old.
Mare Humorum is a lunar mare. The impact basin it is located in is 425 kilometers across.
Mare Serenitatis is a lunar mare located to the east of Mare Imbrium on the Moon. Its diameter is 674 km (419 mi).
Alphonsus is an ancient impact crater on the Moon that dates from the pre-Nectarian era. It is located on the lunar highlands on the eastern end of Mare Nubium, west of the Imbrian Highlands, and slightly overlaps the crater Ptolemaeus to the north. To the southwest is the smaller Alpetragius.
Copernicus is a lunar impact crater located in eastern Oceanus Procellarum. It was named after the astronomer Nicolaus Copernicus. It typifies craters that formed during the Copernican period in that it has a prominent ray system. It may have been created by debris from the breakup of the parent body of asteroid 495 Eulalia 800 million years ago.
Aristarchus, named after the Greek astronomer Aristarchus of Samos, is a prominent lunar impact crater that lies in the northwest part of the Moon's near side. 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 displays unusually bright features when viewed through a large telescope. It is also readily identified when most of the lunar surface is illuminated by earthshine. The crater is deeper than the Grand Canyon.
Arzachel is a relatively young lunar impact crater located in the highlands in the south-central part of the visible Moon, close to the zero meridian. It lies to the south of the crater Alphonsus, and together with Ptolemaeus further north the three form a prominent line of craters to the east of Mare Nubium. The smaller Alpetragius lies to the northwest, and Thebit is to the southwest along the edge of the mare.
Linné is a small lunar impact crater located in the western Mare Serenitatis. It was named after Swedish botanist Carl von Linné. The mare around this feature is virtually devoid of other features of interest. The nearest named crater is Banting to the east-southeast. The estimated age of this copernican crater is only a few tens of millions of years. It was earlier believed to have a bowl shape, but data from the LRO showed that it has a shape of a flattened, inverted cone. The crater is surrounded by a blanket of ejecta formed during the original impact. This ejecta has a relatively high albedo, making the feature appear bright.
Bailly is a lunar impact crater that is located near the south-west limb of the Moon. It was named after French astronomer Jean S. Bailly. The oblique viewing angle gives the crater a foreshortened appearance, and the location near the limb can limit visibility due to libration. The most favorable time for viewing this feature is near the full moon when the terminator is crossing the crater wall.
Archimedes is a large lunar impact crater on the eastern edges of the Mare Imbrium. Its diameter is 81 km.
Regiomontanus is an ancient lunar impact crater located in the southern highlands region to the southeast of Mare Nubium. It is joined at the chaotic northern rim by the crater Purbach, and to the south-southeast is Walther.
Galilaei is a lunar impact crater located in the western Oceanus Procellarum. Some distance to the southeast is the crater Reiner, while to the south-southwest is Cavalerius. Northeast of the crater is a meandering rille named the Rima Galilaei. To the southeast is the unusual Reiner Gamma formation, a swirling arrangement of light-hued ray-like material.
Purbach is a large lunar impact crater located in the rugged southern highlands of the Moon. The distorted crater Regiomontanus is attached to the southern rim. To the northwest is Thebit and just to the northeast lies La Caille.
Democritus is a lunar impact crater that is located on the northern part of the Moon, just to the north of the Mare Frigoris. Just to the south of Democritus is the lava-flooded crater Gärtner, which forms a bay on the mare. Directly to the north is Arnold, another flooded formation.
Fontenelle is a lunar impact crater that is located along the northern edge of Mare Frigoris, in the northern part of the Moon. To the northeast is the remnant of the crater Birmingham. Due to its location, this crater appears oval in shape when observed from the Earth because of foreshortening.
Sinus Medii is a small lunar mare. It takes its name from its location at the intersection of the Moon's equator and prime meridian; as seen from the Earth, this feature is located in the central part of the Moon's near side, and it is the point closest to the Earth. From this spot the Earth would always appear directly overhead, although the planet's position would vary slightly due to libration.
Michael van Langren, also known as Michiel Florent van Langren was an astronomer and cartographer of the Low Countries in the service of the Spanish Monarchy. His Latinized name is Langrenus.
Selenographia, sive Lunae descriptio was printed in 1647 and is a milestone work by Johannes Hevelius. It includes the first detailed map of the moon, created from Hevelius's personal observations. In his treatise, Hevelius reflected on the difference between his own work and that of Galileo Galilei. Hevelius remarked that the quality of Galileo's representations of the Moon in Sidereus nuncius (1610) left something to be desired. Selenography was dedicated to King Wladyslaw IV and along with Riccioli/Grimaldi's Almagestum Novum became the standard work on the Moon for over a century. There are many copies that have survived, including those in Bibliothèque nationale de France, in the library of Polish Academy of Sciences, in the Stillman Drake Collection at the Thomas Fisher Rare Books Library at the University of Toronto, and in the Gunnerus Library at the Norwegian University of Science and Technology in Trondheim.
democritus moon valleys and mountains.
Riccioli and Grimaldi's maps were not the first of the Moon. In 1645 Michael Van Langren published what is acknowledged as the first map of the Moon, introducing a scheme of names for its features, setting it apart from earlier unlabelled drawings of the Moon. Two years later, in 1647, Johannes Hevelius published maps of the Moon in his work Selenographia.
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