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
