Triesnecker Rilles on the MoonThe week of September 11-17 takes us from Day 21 to Day 27. The Moon will not be in a good position for viewing until about 1:00 AM on Tuesday. This week we will highlight the Triesnecker rilles, visible early Tuesday morning.

Rimae Triesnecker: [NE/J10] What a great place to poke around with your telescope! This is such a complex system of rilles that it looks like a railway switchyard! Before looking at the footnote, which do you think came first, the crater or the rilles?

Rimae TriesneckerThe width of the rilles measures between one-half mile and one mile. The largest rilles can be seen in a three-inch refractor, but the whole system requires larger apertures and good seeing. There are at least nine rilles crisscrossing each other. Make a sketch of how many you can see, then come back later and try to improve on it.

Scientists are not sure how the Triesnecker rilles developed. Their origin still remains a mystery, but the consensus is they are not grabens (as the Ariadaeus rille is [NE/J11]). Enjoy them as one of the Moon’s many enigmas.


On Tuesday morning, just on the edge between nautical and civil twilight, the Moon will occult Aldebaran and will be visible before or during dawn in the west.

1 There is a rille approaching Triesnecker’s northeast rim that looks like it has been interrupted by the crater, suggesting that the rilles were there first.

2 graben: [German for ditch] an elongated depression between two parallel fault lines. These lines occasionally pull apart with such force that the ground between them drops. Rima Ariadaeus [Visible Monday morning & on Day 6; NE/J11] and the Alpine Valley [Visible tonight & Day 7; NE/E10] are excellent examples of grabens. Lunar grabens have their counterparts on Earth. Examples are Death Valley, parts of the Rhine Valley, and the Rift Valley in Africa.


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
Triesnecker Rilles on the Moon: Looks Like a Railway Switchyard
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