A guide to the Moon’s Aristarchus Crater

Facts about Aristarchus Crater and images of this fascinating lunar feature.

Schroter's Valley by Julie Straayer, Albany Creek, Australia. Equipment: Skywatcher 150 Pro Maksutov, kywatcher AZEQ 5 mount, Starguider 12mm eyepiece, Orion Steadypix EZ smartphone adapter, Sony Xperia Z3 smartphone

Aristarchus is by far the brightest crater on the entire Moon and can always be seen whenever it is in sunlight.

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It also shows up when the Moon is lit by earthshine, and many astronomers have mistaken it for a volcano in eruption; even Sir William Herschel fell into this trap.

It lies in the Oceanus Procellarum but is not isolated by any means; Aristarchus lies close to Herodotus, a crater of much the same size but without Aristarchus’s brightness.

For more on lunar observing, read our guide on how to observe the Moon or how to photograph the Moon.

Aristarchus Crater on the Moon
Aristarchus is one of the Moon’s youngest craters, with an estimated age of 450 million years

Facts about Aristarchus Crater

  • Size: 40km
  • Age: 450 million years
  • Location: Latitude 23.7°N, longitude 47.4°W
  • Recommended observing equipment 4-inch telescope

Brightest crater on the Moon

Aristarchus is the brightest crater on the Moon, but why is it so bright? Simply because it is very young, formed at a late stage in the Moon’s evolution.

Aristarchus is thus one of the very youngest craters on the entire lunar surface. It is well formed, with high terraced walls and a central peak.

Its age is believed to be about 450 million years, which is very young by lunar standards.

Aristarchus and the Western Limb of the Moon by Mike Jennings, W. Yorkshire, UK. Equipment: Celestron C8 SCT, QHY5.
Aristarchus and the Western Limb of the Moon by Mike Jennings, W. Yorkshire, UK. Equipment: Celestron C8 SCT, QHY5.

Its position on the disc means that it can be seen for a good part of every lunation, and it is fascinating to draw or photograph it from night to night and note the apparent alterations due to changes in solar illumination.

The adjacent crater Herodotus is also well formed, but there is no marked central peak.

An image of Aristarchus Plateau, as seen by the Lunar Reconnaissance Orbiter. The patch lies northwest of the Aristarchus crater, seen in the bottom right. Credit: NASA (image by Lunar Reconnaissance Orbiter)
An image of Aristarchus Plateau, as seen by the Lunar Reconnaissance Orbiter. The patch lies northwest of the Aristarchus crater, seen in the bottom right. Credit: NASA (image by Lunar Reconnaissance Orbiter)

Also in this area is the longest sinuous valley on the Moon, named in honour of the German astronomer Johann Schröter.

In a way this is misleading because the crater named after Schröter is a long way away in an entirely different part of the Moon.

Aristarchus (c310-230 BC) himself, the Greek astronomer from Samos, was the first to maintain that Earth revolved around the Sun and rotates on its axis, while Herodotus (c485-425 BC) was a Greek historian.

Aristarchus by Amit Sharma, London, UK. Equipment: Celestron C8 AVX, Tru Technology L filter, QHY 5L-II mono
Aristarchus by Amit Sharma, London, UK. Equipment: Celestron C8 AVX, Tru Technology L filter, QHY 5L-II mono

Schröter’s Valley

Schröter’s Valley begins 25km north of Herodotus and gives the impression of a dry river bed.

Starting at a crater 6km in diameter, the valley widens to almost 10km, forming a shape some observers have nicknamed ‘The Cobra’s Head’.

From this it gradually narrows to a width of 55m, finally terminating in a 1km-high bank on the edge of an uplifted area.

Schroter's Valley and Ocean of Storms by John Brady, W. Lancashire, UK. Equipment: Skywatcher 200p, Mono DMK41 CCD, 3x Barlow.
Schroter’s Valley and Ocean of Storms by John Brady, W. Lancashire, UK. Equipment: Skywatcher 200p, Mono DMK41 CCD, 3x Barlow.

Under good seeing conditions a powerful telescope will show a delicate rill on the floor of the valley.

The total length of the valley is 160km with a maximum depth of 1km. Nothing else quite like it can be seen on the Moon.

A number of transient lunar phenomena (TLP) have been seen on or near Aristarchus, and it is well worth keeping a watch for them.

Schroter's Valley by Julie Straayer, Albany Creek, Australia. Equipment: Skywatcher 150 Pro Maksutov, kywatcher AZEQ 5 mount, Starguider 12mm eyepiece, Orion Steadypix EZ smartphone adapter, Sony Xperia Z3 smartphone
Schroter’s Valley by Julie Straayer, Albany Creek, Australia. Equipment: Skywatcher 150 Pro Maksutov, kywatcher AZEQ 5 mount, Starguider 12mm eyepiece, Orion Steadypix EZ smartphone adapter, Sony Xperia Z3 smartphone

Phenomena reported in the crater include periodical obscurations and cloud-like features, which do not persist for long.

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These have never been photographed, and their existence has never been definitely proved. However, looking back at lists of reported TLP, Aristarchus heads the list by a very long way.

Plateau of Aristarchus and the Vallis Schröteri by Fernando Oliveira De Menezes, Sao Paulo, Brazil. Equipment: C11 Edge HD, ASI 174MM, Powermate 4x.
Plateau of Aristarchus and the Vallis Schröteri by Fernando Oliveira De Menezes, Sao Paulo, Brazil. Equipment: C11 Edge HD, ASI 174MM, Powermate 4x.
Sharpening the Perception by Avani Soares, Parsec Observatory, Canoas, Brazil. Equipment: C14 Edge, ASI 224, PM 2X, L filter
Sharpening the Perception by Avani Soares, Parsec Observatory, Canoas, Brazil. Equipment: C14 Edge, ASI 224, PM 2X, L filter