L14 - Sinus Iridum
Although Sinus Iridum (Bay of Rainbows) does indeed appear to be a bay on the northeast shore of Mare Imbrium, it is actually a crater that is tilted into the Imbrium impact basin, then later filled with mare material. The "horns" of the bay are Promontorium Heraclides and Promontorium Laplace.
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Images © Doug Anderson
This image was taken on 10-Jan-2006 through a 203mm Celestron C-8 Schmidt-Cassegrain reflector with a Canon Digital Rebel XT (350D) camera using eyepiece projection through a 26mm eyepiece.