The week of August 12-18 takes us from Day 12 to the end of Day 17. This week we will highlight Mons Rümker and Reiner Gamma.

In spite of its name, Mons Rümker is not really a mountain, it's an extensive complex of domesMons Rümker: [NW/E4] Unfortunately this feature is too close to the Moon’s limb to see it very clearly, so coordinate your viewing with a favorable libration, which will be the case on Monday night. In spite of its name, Mons Rümker is not really a mountain, it’s an extensive complex of domes. The diameter of the formation is over 40 miles. Although there are about a dozen domes here1, through a telescope it looks like a mound with a bumpy surface. Several of the domes have summit pits. Can you make any of them out?

Reiner Gamma: [NW/J4] Lunar swirls are absolutely flat features that cast no shadows but leave enigmatic whorl-like markings on the lunar surface. No known geological process could have created them, and to heighten the mystery, instruments on Apollo spacecraft measured strong magnetic fields directly over the swirls. For the fanciful, they are eerily reminiscent of crop circles. Of the three swirls on the Moon, two have been found to be antipodal features of major impact zones and mascons2. All three of the swirls on the Moon (there are two on the far side) are associated with strong magnetic anomalies.

1 Some sources say 30; how many can you see?

2 Mascons: Areas of the Moon’s surface that were discovered to have unusually strong local gravitational effects due to concentrations of dense, thick lunar material [formed from mas(s) + con(centration)]. Mascons are prevalent around lunar swirls.


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

Andrew Planck

Author and Astronomer Andrew Planck shepherds you to the moon and its mysteries of intrigue and surprise. Learn about the moon’s most fascinating objects, understand how the moon was formed and the names of many of the craters … and why they honor individuals who have changed the course of history.
Andrew Planck
Mons Rümker and Reiner Gamma: Complex of Domes and Lunar Swirls on the Moon

One thought on “Mons Rümker and Reiner Gamma: Complex of Domes and Lunar Swirls on the Moon

  • August 18, 2019 at 1:44 pm

    Really nice blog site, Andrew!
    Don and Judy


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