The Imbrium Basin is the largest impact basin on the Moon’s near side, with a diameter of around 1,160 kilometres. The South Pole-Aitken Basin on the far side is twice as large. The massive impact event that formed Imbrium, one of the most violent in the history of the Solar System that occurred 3.85 billion years ago, left a giant crater which was subsequently infilled by basaltic lava.
Mare Imbrium (Sea of Rains), the huge lava plain that we see today in the Moon’s north-western quadrant, is the most obvious legacy of that ancient, cataclysmic event. Second only in size to neighbouring Oceanus Procellarum (Ocean of Storms), Mare Imbrium is obvious to the naked eye on a 10 day-old gibbous Moon; indeed, Imbrium forms the left eye of...