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Why isn’t the Precession of the Lunar Nodes Uniform with Time?

9 Nov 2014, 14:18 UTC
Why isn’t the Precession of the Lunar Nodes Uniform with Time?
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Question: I am an amateur naked eye astronomer. I teach astronomy to 6th graders, I read a lot on the subject, and I do a lot of experiments and observations to better understand the movements of the sun, moon, etc.
I have been looking at the precession/regression of the lunar nodes and I am a bit confused. I know the nodes are just imaginary lines where the titled orbit of the moon crosses the ecliptic and that they move westward, opposite the direction the earth spins and the moon orbits the earth and the earth orbits the sun and that this takes 18.6 years. I have found vague references to the fact that this is not a steady movement but just moves in that direction on the average to complete one rotation relative to the fixed stars in 18.6 years. I have made some simple models to test this with ephemeris listings of moon phases and when it is in the ascending or descending node, and if checked over long periods of time it does indeed seem to be working its way westward, but if checked over the short term, the position of the moon in the nodes seems to ...

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