The Moon approaches first-quarter phase in a deep blue twilight sky.
When the Moon is nearly at first-quarter phase, the terminator sweeps across some of the most unusual lunar terrain. Aim your telescope toward the region lying between little Mare Vaporum, and the expanse of Mare Tranquillitatis. There you’ll find oddly furrowed features and a couple of badly beat up craters.
Julius Caesar is in particularly rough shape. Its original, circular form has almost been completely erased. And notice the deep trenches to the north and on either side of it. What happened here to cause this mess? The formation of the Imbrium basin is what happened! When a giant impact excavated the Imbrium basin 3.85 billion years ago, ejected debris raked the surrounding terrain, nearly destroying Julius Caesar, neighbouring Boscovich, and creating the nearby linear grooves. You can think of these features as the “smoking gun” that point accusingly back to the centre of Imbrium. It’s a fascinating (if apocalyptic) story, and an wonderful area to explore with your telescope.
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