Eddington is a large feature which appears very close to the Moon’s western limb as seen from Earth. This means it’s affected by the Moon’s libration state, the apparent rock-and-roll motion which allows us to actually see 59% of the Moon’s surface over time.
It’s a crater that has been flooded by lava, resulting in a lunar feature known as a walled plain. Its vast 134km diameter is ringed by highland material, most obvious to the north and west. The eastern rim becomes quite thin, making it tricky to see visually. Towards the southeast, the rim all but disappears into the lava of the Oceanus Procellarum.
As you view Eddington, marvel at the fact that it has a diameter equal to the distance from Birmingham to Cardiff. Under the correct lighting conditions, when you move your gaze closer to the limb it becomes evident that although large, Eddington is dwarfed by the less distinct form of 171km
Struve to its immediate west. Struve is so massive that the former designation of Eddington was Struve A.
Unlike Eddington’s dark and fairly distinctive floor, Struve is harder to discern because it’s covered in lighter material disguising its appearance. There are several small but distinctive craters within Struve that stand out. These include Struve C (11km),
Struve G (14km), Struve L (15km) and Struve M (15km).
Struve F (9km) and Struve K (6km) sit on the rim wall which divides Struve from Eddington. Thereafter, passing into the area bounded by Eddington’s rim, there’s a distinct lack of features. A number of really small craterlets pockmark Eddington’s floor but these are difficult to see with smaller instruments. The largest and most identifiable crater within Eddington’s rim is 12km
Eddington P but it is dark, like its primary, and easily overlooked. All that remains of Eddington P are two sections of rim, one to the east and one to the west. If we could view the crater from above, it would appear like a pair of brackets.
Immediately to the east of Eddington lies the distinctive 43km Seleucus. This is a lovely circular crater with a wide, terraced rim, a flat floor and a central mountain complex. A narrow outline of ejecta frames the crater, which suggests that Seleucus existed before its surroundings were flooded with lava. The Soviet craft Luna 13 touched down on the Moon on Christmas Eve 1966 and its landing site is located approximately 50km to the southeast of Seleucus.
The best view of Eddington occurs – as is the case with many lunar features – when the Sun is low in its sky. This is typically when the phase is approaching full Moon or new Moon. At this time of year, early risers are rewarded with a decent view of the waning crescent, which results in a lovely pre-new Moon view. This coincides with the northern hemisphere’s autumn placing the early morning, waning crescent Moon higher in the sky than at any other time of the year.
“A crater with a diameter the distance of Cardiff to Birmingham”
Eddington pictured with its neighbours, Seleucus and Struve