The Triesnecker Rilles

Jay Albert - April 23, 2013

I’ve always enjoyed observing the moon and did so on the night of February 17, 2013. I was mainly checking certain features which that night experienced illumination and libration conditions very close to those which existed when observers reported lunar transient phenomena. These lunar transient phenomena, or LTP’s, were catalogued by NASA and in two additional catalogues by the British Astronomical Association (BAA). Observing the repeat illuminations of these phenomena is a joint project of the BAA and the Association of Lunar and Planetary Observers (ALPO) in which I participate as a member of ALPO. The main reason to view these repeat illuminations is to be able to explain them and to determine which are normal, which are due to atmospherics here on earth or optical flaws and which might be real anomalous lunar activity. I was also looking for a target to photograph with my Celestron Neximage 5 Solar System camera. I’m still learning how to use this camera and its related software and wanted to experiment with different settings in the image capture software. The night was clear and cold, but the seeing was rather good.

While observing a feature in Sinus Medii, a relatively smooth, 32,000+ square mile plain in the middle of the moon, I noticed that I had a pretty good view of the Triesnecker Rilles, a popular target for lunar observers. The Triesnecker Rilles lie in the Sinus Medii plain next to the crater Triesnecker. These rilles are mentioned in a number of observing guides as the most extensive and intricate rille system on the lunar surface. The photo below was taken through my Celestron 11” SCT with the Neximage 5 camera and processed first in Registax 6, then “tidied up” a bit in Photoshop Elements.


The Triesnecker Rilles run north to south for over 120 miles and are roughly centered near the crater Triesnecker, which is about 16 miles wide and around 8,500 feet deep. You can see the sunlight hitting the upper inner rim of the crater’s west wall, which bulges out of round to its west. The sun is rising on the crater and the shadow from its elevated east wall fills the crater’s interior so that its terraced slopes and central peak cannot yet be seen. This low sun angle also helps to bring the rille system into sharper relief, making it easier to see the fine lines than if the sun were overhead. The rilles are the result of surface fracturing due to subsurface tectonic forces. These forces may be related to the deposition of the volcanic material which created the Medii plain. A good time to view the Triesnecker Rilles is around the first and third quarter moons.

Jay Albert