We visit a large semi-hexagonal crater in the Moon’s central highlands, Albategnius
There are many features on the
Moon that have acquired ‘celebrity’ status because they are genuinely impressive. Other features aren’t given the same credit or attention because they are overshadowed by their more impressive neighbours. One such feature is a walled plain called Albategnius, which can be found almost in the centre of the Moon’s face as we see it from Earth.
If you’re not familiar with this feature that’s no huge surprise. Albategnius is overshadowed by three huge and very famous features directly to its west: Ptolmaeus, Alphonsus and Arzachel. Linked together, and a striking sight in both a small pair of binoculars and a large telescope, these three craters are very popular observing targets, which is why poor Albategnius, just to their east, is usually overlooked. It’s a shame, because it is a fascinating and rewarding feature.
Having said that, not everyone has ignored Albategnius. In 1610
Galileo observed it through his first telescopes and was so impressed by its appearance that he drew it, including it on his famous sketches of the Moon. In modern times Albategnius has been observed and photographed in rather greater detail by many lunar probes, and in 1972 the crew of Apollo 16 took some beautiful images of it as they orbited the Moon on the fifth and penultimate Apollo mission to land on the surface of our planet’s fascinating natural satellite.
Although Albategnius looks like a large crater at first glance it is actually classed as a ‘walled plain’, so it is more like a small sea surrounded by high walls than a simple crater. It is approximately 130 kilometres (81 miles) across, surrounded by jagged walls that tower more than four kilometres (2.5 miles) above the lunar surface, and has lots of smaller craters spattered across its deep floor, around 40 of them.
To the north of the crater floor a tightly clustered trio of these craters runs from west to east, itself presenting a very interesting sight through a small telescope. Albategnius also has another major crater inside its walls. Look down to the southwest and you’ll see the crater Klein, a 43-kilometre (27-mile) steep-walled pit.
In common with many large craters, Albategnius has a central peak, a mountain that stabs up from its floor. Its summit is over 1.5 kilometres (0.9 miles) above the floor and topped with a small crater of its own. Some observers think the mountain range has the shape of a ghost or an angel – you’ll need to look at it through your own telescope to decide if you agree…
Albategnius’ walls are, like those of most large craters on the Moon, very complicated features in their own right, with multiple terraces and ledges breaking them up in every direction and criss-crossed and cut into by valleys and gorges here and there.
So, when can you see this intriguing if overlooked feature for yourself?
As our observing period opens Albategnius is invisible, still deep in shadow. It doesn’t emerge from the darkness until 16 September when the terminator sweeps over it, surrendering it to the sunlight. A day later the plain will be fully visible, its high walls standing out starkly against the surface with the Sun’s rays striking them at a low angle. By the time the Moon is full on 24 September, with the Sun blazing directly overhead, the plain will have been reduced to a mere dark patch. As the days pass and the terminator creeps back towards it from the east Albategnius will become more and more prominent again, until it is swallowed up by the darkness on 2 October and is lost from our view.
Why not take a look at Albategnius this month? True, there are larger and more dramatic features around it, but if you can drag your eyes away from those and dare to stray from the well-worn path you usually follow across the Moon, you’ll find Albategnius a very rewarding ‘off the beaten track’ destination.