Reiner Gamma on the moonThe week of August 22-28 takes us from Lunar Day 25 to Day 1. This week we will highlight Reiner Gamma, lunar swirl on the moon, viewable early Tuesday morning.

Reiner on the moonReiner 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 mascons1. All three of the swirls on the Moon (there are two on the far side) are associated with strong magnetic anomalies.



On Saturday, Mercury will be at its greatest elongation east of the Sun.

1 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
Reiner Gamma – Lunar Swirl on the Moon

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