Mare Undarum in the context of "Nectarian"

Apollonius is a lunar impact crater located near the eastern limb of the Moon. It lies in the region of uplands to the west of Mare Undarum and northeast of the Sinus Successus on the Mare Fecunditatis. It was named after Greek mathematician Apollonius of Perga. It is southwest of the crater Firmicus, and north of Condon.

The outer rim of Apollonius is somewhat worn and is overlain by a pair of small craters (including Apollonius E) across the western wall. The nearly flat interior floor has a low albedo and has been covered by lava. It lacks a central peak or notable small craters across the bottom.

Firmicus is a lunar impact crater that lies in the eastern part of the Moon's near side, so that from Earth it appears oval in shape due to foreshortening. It is, however, very nearly circular. The crater is located to the west of the Mare Undarum, and northeast of the similar-sized crater Apollonius. To the north of Firmicus are the craters van Albada and Auzout. Attached to its northwest rim is the Lacus Perseverantiae, a miniature lunar mare.

The crater is named after 4th century Roman astrologer Julius Firmicus Maternus. The name was formally adopted by the IAU in 1935.

Mare Spumans /ˈspjuːmənz/ (Latin spūmāns, the "foaming sea") is a lunar mare located just south of Mare Undarum on the lunar near side. It is one of the many elevated lakes contained in the Crisium basin, surrounding Mare Crisium. The surrounding basin material is of the Nectarian epoch, while the mare basalt being of the Upper Imbrian epoch. The crater Petit (formerly Apollonius W) is located on the western rim of the mare. This crater is white and surrounded by a well-defined ray system.

Dubyago is a lunar impact crater that lies in the eastern limb of the Moon. It was named after Russian astronomers Dmitry Dubyago and Alexander Dubyago. It appears significantly foreshortened when viewed from the Earth. It lies along the southern shore of the Mare Undarum, to the southeast of the crater Firmicus.

This crater has a somewhat worn outer rim which dips down to a low point along the northern rim, and has its maximum altitude along the eastern side. The most notable aspect of this crater, however, is the dark hue of the interior floor which matches the albedo of the lunar mare to the northwest. This darker shading makes the crater stand out somewhat from its surroundings.