The week of July 17-23 takes us from Day 23 to New Moon. The Moon does not rise until around 1:00 AM on Monday morning, so this week is reserved for intrepid viewers. This week we will highlight the Pytheas secondary craters and the ghost crater Lambert R.

Pytheas secondary cratersPytheas secondary craters: [NW/G7-8] The best place to see secondary craters that have landed within a splash ray is just 25 miles east of the crater Pytheas. There is an alignment of seven or more secondary craters that are obviously confined within a long ray extending from Copernicus, 160 miles to the south. Tonight it is difficult to observe the connection with Copernicus because the craters are visible on Days 9 and 23, but the ray can be more clearly seen later at higher sun angles. So draw the alignment of craters tonight, then come back closer to full Moon on August 7 and fill in the splash ray. (This information will be repeated in the July 31st blog, as few people will be observing at 2:00 A.M.)

Lambert R: [NW/G7; L=21°W] Immediately south of the crater Lambert you will see what is called a “ghost crater”– a circular wrinkle ridge formation indicating an underlying crater that had been completely inundated by the Imbrium lava flows. As the lava cooled, it shrank and the outline of the original crater rim percolated to the top, leaving a ghostly imprint of the original crater.


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
Secondary and Ghost Craters on the #Moon

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