The week of September 17-23 takes us from Day 8 through Day 13. This week we will highlight Catena Davy and Imbrium wrinkle ridges.

Day 8

At the beginning of Day 8 the terminator will have just cleared Plato, Eratosthenes, and Tycho--a profitable time to observe all three craters.The Moon has now entered its gibbous phase and the terminator has become convex toward the west1. Days 7 and 8 present the observer with a cornucopia of detail! At the beginning of Day 8 the terminator will have just cleared Plato, Eratosthenes, and Tycho – a profitable time to observe all three craters. This is also a good opportunity to observe wrinkle ridges that you can see around the eastern side of Mare Imbrium running from Archimedes toward Plato. Many of these wrinkle ridges reveal the presence of hidden mountain ranges, now almost completely buried by lava flows, which formed the inner ring surrounding the impact zone when the Imbrium basin was formed.

This explanation of the origin of catenas was once a controversial idea, but in 1994 Comet Shoemaker-Levy silenced the critics when it slammed into Jupiter leaving the very same type of markingsCatena DavyCatena Davy: [SW/L9] This fascinating crater chain was made when a comet or asteroid was torn into pieces by the gravitational pull of the Earth or the Moon. The alignment of smaller pieces flying through space then slammed into the Moon in machine-gun fashion, leaving a trail of small craters in a straight line. The largest of these craterlets is only a few miles wide and requires high magnification and good seeing.

1 Gibbous: more than half but less than full.


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
Day 8 for the #Moon: Profitable Time to Observe Three Craters

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