(the "sea of waves") is an uneven lunar mare
located just north of Mare Spumans
on the lunar near side, between the crater Firmicus
and the eastern limb. It is one of the many elevated lakes contained in the Crisium basin, surrounding Mare Crisium
. The selenographic coordinates
of this mare are 6.8° N, 68.4° E, and it contained within a diameter of 243 km
The surrounding basin material is of the Nectarian epoch, with the mare basalt being of the Upper Imbrian epoch. The crater Dubyago can be seen on the southern edge of the mare. On the northeastern edge of the mare is the crater Condorcet P.
When Mädler observed this area in the 1830s, he noted variations in the curved dark streaks that form this mare, leading him to speculate that the changes were caused by periodical vegetation.
Mare Undarum was the location of the second catapult in Robert A. Heinlein
's novel The Moon is a Harsh Mistress
. The exact location of the catapult was kept secret and was "A matter of Lunar national security."