RISING MOON
I Building by pounding
SECOND ON LISTS of lunar valleys is Rheita. The more famous Alpine Valley was created when the crust pulled apart, allowing the land to collapse. In contrast, the Rheita Valley is understood to be a nice line of overlapping craters where each impactor fell in rapid succession, obliterating the standard central peaks and rims of the ones formed just before.
Around any young and large impact feature you can find several crater chains pointing radially away from its center, formed as debris from the excavation shoots out in linear sprays like a spoke on a bicycle wheel. The Rheita Valley is the widest such chain, implying that the original impact must have been rather large. It was: Mare Nectaris lies not far to the north.
With a bit of practice and an eye for detail, you can tell that the Rheita Valley is neither the freshest nor oldest feature in the southeastern quadrant of the Moon. On the northeastern flank, note a couple of chopped-off circles. Those must have come before — an idea confirmed by the worn-down appearance of their rims and floors, a consequence of longterm pounding. And Rheita Crater to the northeast and Young D at the south end obviously arrived later because their forms are sharper and
lie on top of the valley, reshaping their parts of it.
Sunrise over the Rheita Valley has occurred by the 11th, but the view on the 12th will be closer to that in the accompanying image. Take another look on the 24th and 25th, when the lighting will be reversed under a setting Sun. This is when you can readily see that the valley points right back to its origin at Mare Nectaris, the Sea of Nectar — a fanciful name for a lake of lava!