L41: Bessel Ray

When a lunar crater is formed by an impact, material from the depth of the crust is forced up and catapulted into the surrounding landscape, forming radial ejecta rays. The ejecta material has a higher albedo than the dark maria, making the rays plainly visible. Many lunar craters are associated with ray systems, most notably Copernicus, Kepler, Proclus and Tycho.

The Bessel Ray is a single ejecta ray running almost north-south through the middle of Mare Serenitatis. On it’s way it touches upon the Bessel crater (in the middle of the sketch), giving it it’s name.

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Sketched 26 April 2015, using a SkyWatcher 10″, and a TeleVue Nagler zoom 3-6 mm. North is down.

Apparently there is some debate concerning the originator of the Bessel Ray: some suggest that it is associated with the nearby crater Menelaus (at the top of the sketch), others that it is part of the extensive ray system emanating from Tycho, far down south.

In an image from the Galileo spacecraft, the ray systems of Copernicus (left), Kepler (far left), Proclus (right)  and Tycho (bottom) are prominent. Mare Serenitatis, with the Bessel Ray, can be seen near the center. Judging from the image the Bessel Ray seems to connect both with Menelaus (the bright spot on the southern shore of the mare) and with Tycho. I am not sure what to make of it, but if think I put my money on Tycho. 

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NASA/JPL
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L25: Messier & Messier A

Situated in the middle of Mare Fecunditatis, this crater couple was created from a very low angle impact, resulting in two distinct ejecta rays. The ray going north-south is associated with the Taruntius crater on the northern shores of the mare.

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Sketch made on 8 March 2014 using a SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm. North is towards the bottom.

L12: Proclus

Rather small but very bright crater on the western edge of Mare Crisum. At high sun Proclus displays a curious looking ejecta pattern. At the eyepiece the pattern resembles a cyclops with very big ears (or horns).

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Sketch made on 4 July 2014 with SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm. North is towards the bottom.

Below is a close up sketch of Proclus made two days earlier.

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Sketch made on 2 July 2014. Equipment as above.

Kepler rays

Observed near full moon Kepler shows an impressive ray pattern, stretching far over the surrounding mare, and blending on the eastern side (left in image) with ejecta rays from neighboring Copernicus.

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Sketch made on 13 March 2014 using a SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm.