The week of October 16-22 takes us from Day 2 to Day 8. This week we will highlight a series of rilles on the moon called Rimae Triesnecker, viewable on Saturday evening.

Triesnecker rillesTriesnecker Rilles: [NE/J10; L=5°E] 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! Which do you think came first, the crater or the rilles?

The 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 above Ariadaeus rille is). Enjoy them as one of the Moon’s many enigmas.


The Orionid meteors will be viewable on Saturday night/Sunday morning.


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 Triesnecker – Series of Rilles on the Moon

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