High Quality Content by WIKIPEDIA articles! Oceanus Procellarum, Latin for "Ocean of Storms", is a vast lunar mare on the western edge of the near side of Earth's Moon. Its name derives from the old superstition that its appearance during the second quarter heralded bad weather. Oceanus Procellarum is the largest of the lunar maria, stretching more than 2,500 km (1,600 mi) across its north-south axis and covering roughly 4,000,000 km2 (1,500,000 sq mi).