Moonwatch
Life on the edge for crater Einstein.
Einstein
Type: Walled plain Diameter: 181km Longitude/latitude: 88.7º west, 16.6º north Age: Undetermined Best time to see: Immediately before full Moon or six days after last quarter with compatible libration. View from the early hours of 24-29 Oct Minimum equipment: 10x binoculars
A quick glance at Einstein’s longitude is enough to indicate that this is a tricky feature to view and image. At 88.7° west, it would usually sit right on the geometric limb as seen from Earth assuming the line of 0° longitude ran down the centre of the Moon all the time. In reality this is not the case as lunar libration – a rocking and rolling motion caused by the tilt and elliptical nature of the Moon’s orbit – regularly swings the position of the zero longitude line east and west slightly. As a consequence, libration rotates Einstein into view at certain times and out of view at others.
This means that features like Einstein in both the east and west libration zones are difficult to observe well. Visibility in these zones only works well when the lighting is oblique and the lunar terminator fairly nearby. In addition, despite Einstein’s vast 181km diameter, its proximity to the limb means we’re seeing it from an extreme angle, so it appears very thin.
Einstein is a large crater best described as a walled plain. From Earth we get to see the inner slopes of its western rim and the outer slopes of its eastern rim. A few details can be seen on its slightly domed floor. As well as a few smaller craters, there’s one whopping example known as Einstein A. This is fairly sizeable itself with a diameter of 51km. Like Einstein, we only get to see the inner slopes of Einstein A’s western rim and the outer slope leading up to its eastern wall. The outer slope of Einstein A is of course, the floor of Einstein.
Our foreshortened view of Einstein tends to give the impression that its rim is fairly intact but images from lunar orbit tell a different story. From a more overhead perspective, the rim is amazingly pockmarked with smaller impact craters. The concentration of the impacts here is so high, it’s quite astonishing how disguised they are under low angle viewing.
Einstein occupies an interesting region of the Moon that bears the brunt of ejecta fallout from the impact that formed Mare Orientale, a massive 300km diameter, concentric-ringed impact basin located further to the south. A lot of the fresh craters in the Einstein region were probably secondary impacts from that which formed Mare Orientale.
Our oblique view of Einstein should make identification of surrounding features challenging but many of its neighbours are substantial in their own right. Touching Einstein’s eastern rim is 61km
Dalton with 47km Balboa A immediately to the east again.
Balboa is the 70km crater located to the north of the midpoint between Dalton and Balboa A. South of Dalton sits the giant form of 94km Vasco
da Gama with 70km Bohr nestled between its southwest rim and the south-southeast rim of Einstein.
Another challenge you might like to take on is trying to make out the irregular and very battered form of 90km
Moseley, which is located immediately north of Einstein. With a lunar longitude of 90.2°, Moseley is even tougher to see than Einstein!
“Libration rotates Einstein into view at certain times and out of view at others”