Lunar Libration?

[Dawson]

In the time-lapse image I’ve composed of Jupiter’s apparent movement in relation to the Moon during last nights conjunction, there appears to be some very minor libration of the Moon; Mare Humorum appears to rotate away from us as the clip cycles and starts again. The time lapse is only 1.5 hours worth of observation and I’m surprised libration is detected in such a short space of time. Is it really libration or is it some artefact?

http://www.dawson.me.uk/MoonJupiter.gif

Capture details: A time lapse of Jupiter passing by The Moon imaged between 22:54 and 00:33 7-8 May 2017, Harlech, North Wales; imaged with Canon 6D with 70-300 lens at 300mm, ISO 100, f/7.1, 1/50th, 100 frames, tracked on equatorial mount, imaged cropped in PIPP and animated gif made in PIPP.

James

[Bill Leatherbarrow]

Hi James,

I’m not sure I can detect what you describe, but I would not expect the effects of libration to be discernible over such a short period. However, the movement of the terminator might be, even at this image scale. Might that be creating the impression of a  shift in the position of Humorum?

Bill

[Dawson]

Bill, that is it of course; zooming right in I can see there is slight movement in the position of the terminator from the start of the clip to the end, moving in a westward direction. That makes much more sense; I will pay more attention next time I’m in one of your talks 🙂

James

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