Selenography

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'. 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 circa 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 began. Circa 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. 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 circa 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. The first serious denominations of the surface features of the Moon, based on telescopic observation, were made by Michel Florent 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 a defense of the Catholic views of the Counter Reformation. In particular he argued against the views espoused by Galileo and Copernicus of a heliocentric universe with perfectly circular orbits. Almagestum Novum contained scientific reference matter based on contemporary knowledge, and contemporary Jesuit educators widely used it. However, the only significant component of the work that is presently authoritative is his system of lunar nomenclature. 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.