Like Theophilus, mentioned later, Gassendi (Figure 10.18) is a distinctive crater sandwiched between a lunar sea and more rugged terrain. In this case the sandwich is between the Mare Humorum and the rugged terrain separating Humorum from the Oceanus Procellarum. Gassendi is an impressive size: roughly 110 kilometers in diameter. However, what makes it a truly outstanding object is the detail on the crater floor. Gassendi is criss-crossed by an intricate network of rilles that only truly reveal their complexity on nights of excellent seeing. There are various hills, peaks, and craterlets, too, that cast a fascinating series of shadows under critical sunrise and sunset illuminations. The significant crater Gassendi A (33 kilometers in diameter) breaks across Gassendi's northern wall as an added feature. Gassendi was the site of a major TLP (transient lunar phenomena) alert on April 30, 1966, when a number of well-known amateur astronomers observed a wedge-shaped orange/red streak extending from the wall of the crater and across the central peaks. The event has never been fully explained. Sunrise on Gassendi occurs roughly three days after the first quarter phase.
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