The major part of Selenographia is the 44 high-resolution charts with 565 labelled features. These combine photograhic images to show how the Moon might appear to an observer equipped with a good telescope. The user guide explains how to use it, and how it fits into the rest of Inconstant Moon, and the site history explains how it was created.
Additionally, a range of smaller-scale maps has been created to illustrate a variety of different aspects of the Moon, its appearance, composition and structure. These are available by clicking the buttons in the navigate panel. The different styles of button represent the different projections used in the maps.
orthographic projection maps show the Moon as it is seen from the Earth, or another point in space. Features in the centre of the map are seen from above, while those at the edges are seen from a lower angle and are foreshortened.
mercator projection shows the whole globe stretched into a rectangle. Features near the top and bottom of the map are stretched horizontally.
equal area projection compresses the features at the centre of the map so that those at the edges occupy an equivalent area.
Some of the topics covered by the maps are straightforward, whilst other are more complicated.
albedo refers to the reflectiveness of a body or material. These maps simply show the albedo of the terrain, with more reflective features showing brighter and the less reflective being darker. Lava-flooded areas, such as the maria, generally have low albedos, whilst younger craters tend to have albedos well above average.
features labels the most prominent craters and plains with their official names.
topography uses false colour to reveal the relief of the Moon's surface. Heights are shown relative to an imaginary, mean lunar surface, equivalent to Earth's sea level. Particularly striking are are differences between the near and far sides, and the massive South Pole/Aitken impact basin.
crustal thickness is closely related to topography. The tallest mountain ranges generally correspond with the areas where the base of the crust is deepest. These massive parts of the crust sink further into the mantle material beneath to establish an equilibrium, a process called isostasy.
gravity anomaly refers to variations in the strength of the gravitational field. The Moon's gravity is particularly uneven. Geoid anomaly is the difference between the "reference spheroid" (an idealised surface modeled by assuming a spinning, fluid lunar body) and the "geoid" (the measured equipotential surface, perpendicular to the action of gravity). Gravity is affected primarily by five factors: latitude, tidal effects, elevation, topography and underlying rock density. The first three can be comparatively easily compensated for. Free air anomaly reflects the remaining two: topography and rock density, while Bouguer anomaly (named after the geologist Pierre Bouguer) eliminates topography, leaving the contrasts in the underlying rock density. Lunar gravity anomalies reveal the existence of mass concentrations (or MASCONs) in many of the large impact basins.
geology uses false colour to assess the distribution of particular spectral characteristics in the lunar regolith (the rocky, dusty coating on the surface). By using particular combinations of characteristics it is possible to infer the relative abundance of key elements such as iron, potassium, and thorium.
landings mostly took place during the sixties and early seventies. Despite many of the impacts not being fully controlled, the "territoriality" of the US and soviet landings is particularly striking. It is easy to draw a gently curved line not unlike that on a tennis ball which completely divides the two areas of influence. It will be interesting to see where future European and Japanese landings take place.
figures are a natural product of the human brain's powerful pattern-making abilities. The "Man in the Moon" is the most widely known figure, though the face most people see is not what is traditionally meant by the phrase. Two more traditional figures are shown, one of which is described by Shakespeare in A Midsummer Night's Dream. Hares and rabbits are another culturally widespread association. The crab is specific to the South Sea islands.
atlases use a variety of different plans to divide the moon into charts or sections. The layouts of a few are provided to allow quick cross-referencing between some of these.
phenomena are very occasionally observed on the Moon. Transient Lunar Phenomena are brief, localised changes in albedo which some people controversially suggest are the effect of geological activity. Sightings tend to be grouped into a number of areas or "hot-spots". Recently, there have been a number of reports of impact flashes on the Moon, and several sightings were confirmed with video in November 1999 and again in November 2001 whilst the Earth and Moon passed through the Leonid meteroid stream.