Moonwatch
Macrobius is a 65km-wide crater situated northwest of the distinctive dark oval of the Mare Crisium. It lies in the complex region of bright highland features interspersed by dark lava ‘lakes’ that sits between Crisium and the eastern region of the Mare Tranquillitatis. It’s a distinctive feature with sharply defined walls. These terrace down to the floor, some 4km below. There appears to have been a significant slippage of material from the walls in towards the centre of the crater as the relatively flat inner floor has half the outer diameter of the crater’s rim.
A small complex of peaks can be seen in the centre of Macrobius, which rise to fairly unimpressive heights of around 800m. As with all lunar features with physical height, the presence of a low Sun causes the central complex to have more prominence. At such times the terraced walls of the crater really come alive, showing intricate shadow detail that is fascinating to try and decode with higher magnifications. The rim is interrupted to the west by 10km Macrobius C, a feature that should be visible using a 4-inch or larger scope.
Crater Tisserand (36km) lies just to the east of Macrobius and is of similar age. Both are
quite elderly compared to dramatic crater Proclus (28km), some 160km south of Macrobius and close to the western edge of the Mare Crisium. Proclus is a bright ray crater, estimated to have formed sometime over the past 1.1 billion years. Its rays spread across the dark lava floor of the Mare Crisium to the east, as well as covering some of the highland terrain to its northwest and north up towards Macrobius.
The flat dark feature to the northwest of Macrobius is the Lacus Bonitatis, the Lake of Goodness, and immediately to its north is Macrobius W (26km). There’s not much of this crater left to see, its insides having been flooded with lava. All that remains is a rather irregular outline, best defined to the north and west. A similar fate appears to have befallen Macrobius S (26km) and T (29km) both east of the main crater and north of Tisserand.
The impact basin of the Mare Crisium is more complex than it looks, with four concentric rings associated with the impact. The inner ring can be seen when the illumination is low over the mare surface. At such times it’s possible to see wrinkle ridges defining this 375kmdiameter feature. The next one, the 500km-diameter Crisium Ring, is defined by the visible edge of the mare itself. Outside of this are two additional rings, but these are very ill-defined and tricky to see.
The outermost is the 1,075km Geminus Ring, which passes through 86kmwide crater Geminus. In between is the vague form of the Cleomedes Ring, which passes through 126km-wide crater Cleomedes. The Cleomedes Ring arcs around the Mare Crisium, passing through Macrobius – though we have to emphasise that the outer rings are extremely difficult to make out.
“When the Sun is low the terraced walls of the crater really come alive, showing intricate shadow detail”