L44: Mersenius

Mersenius is located west of Mare Humorum not far from the moon’s western limb. It is of average size but still rich in detail. The crater walls are broad and terraced; the floor has been flooded with lava and bulges markedly upwards in the middle.

My observation was done under excellent conditions with steady, transparent skies and favorable illumination. The terraces were prominent, especially on the western side (right i sketch). The convex shape of the floor was indicated by a soft shadow tracing the walls in the northern half of the crater. Two lighter rays were also clearly visible on the floor. (After checking up on the observation it seems that the northern and thinner ray, is a rille rather than a ray.) Several secondary craters were also seen, most notably Mersenius H on the southern part of the rim, and Mersenius L adjacent to the crater on the northern side.

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Sketch made on 25 September 2015, UT 21:00, using a SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm. Seeing 4-5/5. South is up.
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L13: Gassendi & Mare Humorum

A rather quick sketch of Mare Humorum and a number of prominent craters, including Mersenius and Gassendi. The seeing for once was perfect, but after having finished several other sketches the same evening my endurance failed me.

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Sketch made on 4 October 2014 using a SkyWatcher 10″ and a TeleVue Nagler zoom 3-6 mm.

Below is an earlier sketch focusing on the Gassendi crater. This was my first try at a close up sketch of one of the larger craters. At the time seeing was perfect, but light clouds kept interfering.

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Sketch made on 10 February 2014 using a SkyWatcher 10″ and Baader Genuine Orthos 5 & 9 mm. North towards the bottom.