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 are uncertain by several kilometers. Today, selenography is considered to be a subdiscipline of selenology, which itself is most often referred to as just "lunar science." The word selenography is derived from the Greek lunar deity Selene and ? (grapho, “I write”).The idea that the Moon was not perfectly smooth can be traced as far back as approximately 450 BC, when Democritus believed that there were "lofty mountains and hollow valleys" on the Moon. However, it was not until the end of the 15th century when serious study of selenography began. Around 1603, William Gilbert compiled the first lunar drawing based on naked-eye observations. Others soon followed, and when the telescope made its appearance, drawings were begun that at first were not very accurate, but soon became better as optics improved. In the early 18th century, the librations of the Moon were measured, showing that more than 50 percent of the lunar surface was visible to observers. In 1750, Johann Meyer produced the first reliable set of lunar coordinates that would enable astronomers to locate features on the Moon. The systematic mapping
f the Moon officially began in 1779 when Johann Schroter started making meticulous observations and measurements of the lunar features. The first published large map of the Moon, four sheets in size, was published in 1834 by Johann Heinrich von Madler, who followed this up by publishing a book entitled, "The Universal Selenography. All measurements were done by direct observation until March 1840, when J.W. Draper, using a five-inch reflector, produced a daguerreotype of the Moon, thus introducing photography to the astronomical world. At first, the images were of very poor quality, but like with the telescope two hundred years earlier, they very quickly became better. By 1890 lunar photography had become a recognized branch of astronomical research. The 20th century brought more advances to study of the Moon. In 1959, Russia's Luna 3 sent back the first photographs of the far side of the Moon, giving the world the first glimpse of the until-then unseen side of our satellite. The United States launched the Ranger spacecraft between 1961 and 1965 to take photographs right down to the instant they impacted the surface, the Lunar Orbiters between 1966 and 1967 to photograph the Moon from orbit, and the Surveyors between 1966 and 1968 to take photos and soft land on the lunar surface. The Russian Lunokhods 1 (1970) and 2 (1973) traversed almost 50 km of the lunar surface, obtaining detailed images of the lunar surface. The Clementine spacecraft obtained the first near global map of the Moon's topography, as well as multispectral images. All of these missions sent back photographs that were of increasingly better resolution.