Lunar libration

[Dawson]

I was asked if the lunar libration is exactly the same each lunar cycle – I said I didn’t know, but I knew somewhere where I’m sure we could find the answer…

I explained about the changes in apparent size of the Moon as it’s distance from the Earth varies, but I am totally ignorant on the similarity of the wobble between lunar cycles.

Thanks for any help.

James

[Bill Leatherbarrow]

Hi James,

Good question!

The short answer is that because of the combination of various librations (libration in longitude, libration in latitude, and diurnal libration) the cycle of librations does not map onto the Moon’s monthly cycle. A more detailed explanation will require someone with a greater grasp of celestial mechanics and maths than I possess. Perhaps someone such will be along soon!

Bill

[Author]

Posts