Astronomy Now - January 2021

Highlights: Mountains on the Moon

When: evenings of 20 and 21 January

What’s special: Everybody loves mountains, whether as mountain ranges such as the magnicent
Himalayas, home of Mount Everest, the highest peak on Earth, or isolated structures such as Mount
Kilimanjaro, the tallest such mountain (actually it’s an extinct volcano).

e Moon has plenty of eye-opening mountains of its own, with several spectacular ranges that are
superbly seen through a pair of binoculars or a small telescope, and numerous isolated tall peaks, or
massifs, some of which are readily accessible in amateur instrumentation.

How to observe: Montes Apenninus (the lunar Apennines) majestically guard the south-eastern
shore of Mare Imbrium (Sea of Rains). is mountain range is the largest and most striking on our
satellite, ranging for 600 kilometres from Promontorium Fresnel in the north to the peaks east of
crater Eratosthenes.

Montes Apenninus’ highest peaks include the impressive Mons Huygens (5,500 metres), the highest
peak on the Moon, and Mons Hadley (4,600 metres), lying close to its eastern extremities. It was
near the latter, alongside Hadley Rille in the shadow of the Apennines, that Apollo 15 landed in
July 1971. To pinpoint Montes Apenninus’ location, look to the south of the prominent triangle of
craters Aristillus, Autolycus and Archimedes. Sunrise over the extreme eastern end of Montes
Apenninus occurs on 20 January at rst quarter phase, barely illuminating Mons Hadley and Hadley
Rille but not all the aforementioned craters. Under good seeing, a 150mm (six-inch) telescope can
reveal the snake-like Hadley Rille, though it can get obscured by the westwards-cast shadow of
towering Mons Hadley at this time.

After following in Apollo 15’s deep footprints, look to Montes Caucasus, another prominent chain
that forms a continuation of Montes Apenninus to the north-east (to crater Eudoxus) on the north-
western shore of Mare Serenitatis (Sea of Serenity).

By the following evening, 21 January, the lunar morning terminator on a 8.5-day-old Moon (phase
58.2 per cent) has advanced westwards to reveal Montes Apenninus in their entirety, yielding a great
sight through any size telescope as the morning illumination casts shadows westwards. A 150–200m
(six- to eight-inch) telescope, operating at a power of around 150× to 200×, zooms in nicely on
Mons Huygens and just to its west Mons Ampère (3,000 metres). ese peaks lie to the east and
south-east, respectively, of the diminutive (4km-wide) crater Huxley.

Moving north along the terminator brings us to the smooth and dark-oored crater Plato. Just to its
south lies the isolated peak of Mons Pico, which towers 2,400 metres or so above the northern plain
of Mare Imbrium. Look out for its spectacular, westwards-cast shadow extending to the lunar
terminator. Close by to the south-east is Mons Piton (2,300 metres), another stand-alone massif
that’s well worth observing; it lies just south-east of the crater Piazzi Smyth.

Montes Apenninus are a magnicent mountain range seen to the left centre below the prominent triangle of craters Aristillus,
Autolycus and Archimedes. Montes Caucasus, seen in the top right corner, curve away to the north-west.

Mons Huygens in the Montes Apenninus is the tallest peak on the Moon.

Mons Pico, Pico b and Mons Piton are isolated peaks on the plain of Mare Imbrium, south of crater Plato.

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Highlights: Mountains on the Moon

January 2021

Astronomy Now