January’s top lunar feature to observe
Nasireddin
Type: Crater
Size: 53km
Longitude/Latitude: 0.1o E, 41.0o S
Age: Approximately 3.8–3.9 billion years
Best time to see: First quarter (10 January) or six days after full Moon (24 and 25 January)
Minimum equipment: 50mm refractor
Nasireddin is a 53km crater located in the rough textured southern badlands area of the Moon. It is a great example of how some lunar features overlap others. When this happens, it’s logical to conclude that the overlapping feature is younger than the feature overlapped, a technique used to determine the relative age of surface features.
In this case, Nasireddin overlaps 65km Huggins, the western edge of Nasireddin’s rim stretching onethird of the way across the larger crater’s diameter. Being the overlapped crater, the age of Huggins is estimated to be greater than 3.9 billion years.
To the north lies Miller, a 75km crater that presents more of a problem. If you look carefully at Miller and Nasireddin, they appear to touch, but it’s not obvious whether an overlap has occurred. If anything, the curving edge of Miller looks subtly dominant in that its natural curve persists along the co-joined section. Consequently, Miller’s age is estimated to be in the same range as Nasireddin, about 3.8–3.9 billion years.
Nasireddin has a sharp rim edge exhibiting plenty of terracing. Compare Nasireddin’s rim with that of Huggins. The latter looks much smoother and rounded without much obvious terracing. Miller looks like a larger version of Nasireddin.
Nasireddin’s central floor area is very rough, its texture appearing richly detailed when the Sun’s angle is low. There are a number of small craterlets visible here, along with many hill bumps. The crater is described as having a central mountain complex, but it’s not immediately obvious where this starts and the surrounding hills end. Again, compare Nasireddin to Miller to the north. Miller’s central complex is much better defined, with smaller peaks surrounding a main peak.
Nasireddin has an unusual rim illumination around co-longitude 2.6˚. Lunar co-longitude is a value which indicates the location of the morning terminator; that’s the one which creeps across the Moon’s face from new Moon, through the waxing phases until full Moon. It’s measured in degrees from when the terminator touches the Moon’s line of zero longitude, the lunar equivalent of Earth’s Greenwich meridian.
At first-quarter Moon, the co-longitude value is close to 0˚. It then increases to approximately 90˚ at full Moon, 180˚ at last quarter and 270˚ at new Moon. The ‘approximately’ label is due to lunar libration,
which causes the Moon’s prime meridian to shift relative to the more geometrically defined phase positions. At colongitude 2.6˚, the Moon’s early morning light catches regions around Nasireddin’s edge, causing the rim outline to appear as a series of short dashes, a clair-obscur effect we’ve called the ‘broken arc’.
Nasireddin lies 270km east of the 86km ray crater Tycho. The rugged nature of Nasireddin doesn’t allow ejecta debris from the much younger Tycho to stand out, and this is evident on the dark floor of the 126km walled plain of Stofler, east of Nasireddin.
