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november: farside closeup
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It has been known since prehistoric times that the Moon's face is 'blemished' with large dark marks. Shortly after the invention of telescopes nearly 500 years ago, these maria were seen to be areas of dark, smooth rock, relatively free of the craters which cover the lighter surrounding uplands.
It was a surprise, during the 20th century, to discover that the lunar farside has very few maria, and is almost entirely upland, as in this Apollo 11 of the 30km (19 mile) wide 'crater 308'.
The Moon exhibits 'captured rotation': over billions of years the Earth's gravity has pulled and deformed the Moon until it rotates once on its axis for every once it revolves around the Earth, and one slightly bulging hemisphere is compelled to always face the Earth.
It is generally believed that these same processes have made the crust of the bulging nearside thinner, and caused the eruption of seas of molten rock into large impact basins to create the maria, although the process is not yet fully understood.
Image: NASA.