365 Days of the Moon -- August 09, 2014
Mare Imbrium wide view
Mare Imbrium (Sea of Rains) is the classic prototype for maria that formed within an impact basin. It is obvious that circular Mare Imbrium is
bordered by curved adjoining mountain chains. With hindsight, we now know these mountains are actually the rim of a impact basin. By definition, a
lunar basin is any huge crater exceeding 300 kilometers across. Imbrium more than fits the bill. In the billion years following the creation of
the Imbrium Basin some 3.8 billion years ago, the excavation was filled by hundreds of lava eruptions until it was smoothly paved over like we see it
But this seemingly obvious explanation for this feature's origin was long in coming. It was 280 years after the perfection of the astronomical
telescope before a geologist, not an astronomer, deduced the truth about the origin of Mare Imbrium. In the 1890's, Karl Grove Gilbert, chief
geologist for the US Geological Survey, concluded that Imbrium formed by of a colossal collision on the Moon. But Gilbert's discovery was ignored
for another half century until Ralph Baldwin independently came to the same conclusion in the late 1940's. Indeed, the universal acceptance of
the impact origin of lunar features was not complete until the Apollo expeditions to the Moon. Sometimes the obvious takes a while to sink in.
This image is a montage of two images taken through a Celstron 11 Edge
HD and Skyris 274M camera.
Image copyright Robert Reeves 2014
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