The week of April 5-11 takes us from Lunar Day 24 to New Moon, so you’ll have to do early morning viewing. This week we will highlight Rimae Ramsden and the Milichius domes in the SW quadrant of the Field Map, SE of Mare Humorum, viewable early Tuesday morning.

Rimae Ramsden, a network of rilles just east of the crater RamsdenRimae Ramsden: [SW/N6-7] If you follows Rima Hesiodus to the southwest it will point to Rimae Ramsden, a network of rilles just east of the crater Ramsden. Like the Triesnecker rilles [Day 6/J10], scientists have no explanation of how they got there.

Milichius is one of the more significant domes on the MoonMilichius domes: [NW/J7; L=31°W] After visiting Rimae Ramsden, go straight north to the crater Milichius (it’s about two Copernicus-crater-diameters to the west of Copernicus). To its immediate west you will find a few domes, chief of which is Milichius Π (Pi), one of the more significant domes on the Moon. Milichius Π is about 5 miles wide and has a summit crater a little over 1 mile in diameter. Because it is steeper than the average dome, it is a little more prominent and will cast a longer shadow. (At the average distance of the Moon the summit pit would be about 0.9 arc-seconds in diameter, so it will be a challenge but keep trying.)

About 60 miles north of Milichius Π you will run into another dome field just south of the 20-mile crater T. Mayer [H7]. This entire area, from Hortensius to T. Mayer, is chock-a-block full of domes and will reward close scrutiny.


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
Rimae Ramsden and the Milichius Domes on the Moon
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