Boundary of <a href="https://en.wikipedia.org/wiki/Mare_Serenitatis" class="extiw" title="en:Mare Serenitatis">Mare Serenitatis</a> (at the top) and Mare Tranquillitatis (at the bottom). Lava of different albedo is seen. The brighter lava is younger. Photo by <a href="https://en.wikipedia.org/wiki/Apollo_17" class="extiw" title="en:Apollo 17">Apollo 17</a> (1972). Width of the photo is approximately 100 km, north is approximately up.
NASA (photo by Apollo 17)
cropped version of <a href="//commons.wikimedia.org/wiki/File:Mare_Serenitatis_AS17-150-23069.jpg" title="File:Mare Serenitatis AS17-150-23069.jpg">File:Mare Serenitatis AS17-150-23069.jpg</a>