Sinus Iridum lying on the northwest periphery of Mare Imbrium is an impressive bay in the form of a half-crater measuring approximately 400x260 km and representing an area of approximately 237,000 square kilometers. It is dominated to the north by the Montus Jura mountain range whereas to the south it blends into Mare Imbrium by sinking by about 600 meters lower than the mare floor at its intersection point, thus suggesting a later lava flow from the latter towards the former (also note the differential color on either side in the image below). Sinus Iridum is characterized with 1700-meter tall Promontorium Heraclides to the west and the 2600-meter tall Promontorium Laplace to the east. The crater gracing the northern bank and slightly east of center is Bianchini measuring approximately 38 km in diameter. To the north of Sinus Iridum we have Mare Frigoris and the 39-km impact crater Harpalus.

Note: The Bay of Rainbows was host to the Soviet probe Luna 17 which soft-landed on Nov 10, 1970 and released the mobile laboratory Lunakhod 1. A complete enumeration of all landing sites for Apollo, Luna and Surveyor craft is available elsewhere on this site.