Note: A full account of this research can be found in:

Stooke, P.J. "Mappaemundi and the Mirror in the Moon". Cartographica, 29 (2), 20-30, 1992.

A popular summary was published as:

Stooke, P.J. "The Mirror in the Moon". Sky and Telescope, 91 (3), 96-98, 1996.

It was widely (though certainly not universally) believed in the ancient and medieval worlds that the Moon was a mirror of some kind, floating in the air, which reflected an image of Earth's lands and seas. Some prominent people (e.g. Leonardo da Vinci) wrote opposing the idea, but it crops up from time to time in european and arab sources from roughly the time of Aristotle (325 BC) to the late 19th Century (as a late survival in folklore). The originator may be Clearchos, a pupil of Aristotle's.

If the dark maria are thought of as a reflection of Earth's land masses, how do they correspond with actual lands? Several arrangements are possible, but one of the most likely has the eastern maria (Crisium, Fecunditatis, Nectaris) corresponding to Africa, and the western maria (Imbrium, Nubium and Oceanus Procellarum) representing Asia.

The possible connection with Africa receives remarkable support from an unusual arabic world map drawn in 1570 and now in the Bodleian Library. See the Sky & Telescope article for a nice reproduction. A comparison of the Bodleian map with the Moon (Figure 1) illustrates this. Note that the Moon has been reversed to take the reflection into account. Especially interesting is the representation of southern Africa as a great double peninsula, quite unlike the actual shape of Africa but similar in appearance to the maria Fecunditatis and Nectaris. There is even a large island in the South Atlantic which might represent Mare Crisium. Another island on the extreme west edge of the Bodleian map is described on the map as the place where souls of the dead reside, another belief long held about the Moon. This latter island is actually in a better position to represent Mare Crisium. Various other arab maps of the period 1100-1500 also show southern Africa as a pair of peninsulas.

It is possible that the name Mountains of the Moon given to the sources of the Nile on maps of the Ptolemaic tradition is a reference to this belief - they were the mountains which could be seen in the Moon. A curious passage in Homer's Iliad might also be cited as a very early reference to this idea - the 'Ethiopians' (Africans) are said to inhabit two lands, one where the sun rises, one where it sets, in other words in the east and west. If this is true, the tradition is remarkable ancient, or is a later interpolation.