Moonwatch
Crater Fontenelle
THE 38KM-WIDE crater Fontenelle sits on the northern shore of Mare Frigoris, the Sea of Cold. The most familiar feature nearby is the darkfloored crater Plato (100km), which sits in the rough terrain that separates Frigoris from the massive Imbrium Basin to the south. Look north and slightly west of Plato, across the Sea of Cold, and you’ll arrive at Fontenelle.
The crater is circular with a flat floor, and a small and low mountain complex at its centre. The rim of the crater rises about 1.5km above the floor, and the southwest edge is interrupted by a line of three tiny craterlets that head southwest, ending close to a bright feature that juts into the mare.
Being relatively close to the lunar limb, Fontenelle’s appearance changes with the prevailing libration. When libration is favourable it may be possible to detect rilles, or cracks, in the crater’s floor, although you’ll need highmagnification and a steady atmosphere to see them visually. A small mountainous region can be seen outside the rim to the northwest.
Approximately 60km west of Fontenelle lies Fontenelle D (17km). This crater forms a pair with the slightly smaller Fontenelle B (14km), which sits immediately south. Fontenelle D is a tricky concentric crater – a feature that shows one rim concentrically positioned within another. In this case the second rim is not obvious at first and requires oblique lighting to see convincingly. The inner crater is extremely shallow and has half the diameter of Fontenelle D.
The region immediately to the north of Fontenelle includes a large expanse of flat lava. The boundaries of this region are quite high and at times when the Sun is low in the lunar sky it will cast dramatic shadows across the lava below. To the east of this region is Fontenelle A (21km). A line drawn from Fontenelle through Fontenelle A will eventually reach the crater Anaxagoras (51km).
A wrinkle ridge passing southeast-northwest across the floor of Frigoris comes to an abrupt end at the southeast wall of Fontenelle. Above this is a curious area of flat lava with several elevated mountains, hills and curved formations. The northwest and northeast boundaries of this region have an approximate linearity and it’s likely that they form two sides of an unofficial lunar feature known as Mädler’s Square. The largest elevated structure southeast of Fontenelle, formerly known as Fontenelle Epsilon, rises 0.6km above the surrounding lava floor and marks the square’s southern corner. Heavily eroded crater Birmingham (93km) sits east of Fontenelle, its southwestern rim forming the final side of the square.
“When libration is favourable it may be possible to spot rilles in the crater floor”