Moon tour
MARE CRISIUM
The lunar sea offers spectacular bright views this month
Despite their name, the prominent lunar features known as ‘seas’ – ‘maria’ in Latin – aren’t stretches of liquid water. They’re vast pools of dark lava that flooded low-lying areas, but mainly impact basins, several billion years ago. These lava flows have long since solidified. It was only in ancient times – long before telescopes were first invented – that these dark patches, so clearly visible with the unaided eye, were speculated to be marine regions. But for more than 400 years we have known that the Moon’s seas are decidedly solid areas – no waves lap at their shores and no wind billows across their expanses.