Altai Scarp moon craterThe week of November 30 – December 6 takes us from Lunar Day 15 to Day 21. This week we will highlight the crater Piccolomini and the Altai Scarp, viewable on Friday evening, Day 19.

The moon crater Rupes Altai is a beautiful and conspicuous fragment of the original ringsAltai Scarp (Rupes Altai): [SE/M12] Viewable even through small telescopes, the Altai Scarp is a spectacular example of how shock waves from a major impact can compress the surrounding terrain into a series of outwardly expanding rings. Nearly 3.9 billion years ago a large asteroid or comet slammed into the Moon and dug out the Nectaris Basin. Shock waves rapidly expanded through the surrounding terrain and became frozen in place, producing a classic multi-ring basin. Rupes Altai is a beautiful and conspicuous fragment of the original rings. In truth, it is a circular mountain range whose highest peaks rise to 13,000 feet! But you must catch the scarp under a low Sun, it’s majesty fades quickly. View it Friday evening, then revisit the area around Day 5 at lunar sunrise when the face of the scarp is fully illuminated. Which day, do you think, shows the scarp to its best advantage?

Piccolomini moon craterPiccolomini: [SE/M13] The Altai Scarp terminates on its southern end at Piccolomini (55 mi. in diameter.), a beautiful and complex crater with a substantial central mountain peak, terraces, and a smooth convex floor. Notice how there is a great deal more turmoil around the southern rim of Piccolomini. Can you see the tiny craterlet just touching the northwest base of the central mountain?


It is highly recommended that you get a copy of Sky and Telescope’s Field Map of the Moon, the very finest Moon map available for use at the telescope. It is available for $10.95 at and on Amazon. All features mentioned in this blog will be keyed to the grid on the Field Map and will look like this: Plato: [NW/D9]

Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission

Andrew Planck
Moon Craters Piccolomini and Altai Scarp

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