The Moon, 18 days past new, is now a trio of days past full phase. The terminator, the
sunset line, where shadows are long, runs down the picture at right. At the top (north)
lies dominant Mare Imbrium. Cascading down and to the right are three more large lava-filled
basins, Mare Serenitatis, Tranquillitatis, and Nectaris. Mare Nubium is the prominent dark space toward
lower left, while Cognitum is up and to the left of it. In the far north Mare Frigoris
lies above the mountains (the lunar Alps) that form Imbrium's northern boundary.
Four youthful "rayed" craters make their
promient marks, the rays strings of secondary craters and debris created by the violent impacts
that have not had time to darken with age.
Copernicus is the brightest one toward the top; Kepler is to the left of it, Aristarchus to
the upper left. The king of them all, Tycho (just
100 or so million years old), is toward lower left, one of its rays extending
even across Mare Serenitatis at upper right. Far more ancient craters, which go back to the heavy
bombardment early in the history of our 4.6-billion-year-old
Solar System, line up along the terminator. Particulary noticeable
are paired Hercules (top)and Atlas toward upper right. Toward the lower right find Fabricius, the
lowest of a distinctive trio that lies at the upper edge of a larger ruined structure. Back to the
north, Plato lies in the middle of the lunar Alps, obviously formed after the Imbrium basin
was created.
To set the scale, Mare Imbrium is 1150 kilometers (just over 700 miles) across, Tycho 85 km.
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