colongitude

plural colongitudes

1. astronomyThe longitude of the morning terminator (division between illuminated and dark regions) on the Moon, as measured in degrees westward from the prime meridian.

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   The colongitude is the longitude of the terminator, that is the location of the separation between the lunar day and night. As the Moon rotates around the Earth with respect to the Sun, the terminator slides westward by 0.5° per hour (“westward” stands here for selenographic coordinates, lunar West is on our left hand if we observe the Moon from the northern hemisphere).

   2016, Nicolas Dupont-Bloch, Shoot the Moon: A Complete Guide to Lunar Imaging, page 16