moon 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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By Jim Kaler. Return to MoonScapes, Skylights, or STARS.