What is the cause of variations in lunar eccentricity?

  • Thread starter fizzy
  • Start date
187
13
I just tried the sim on the laptop : older Fedora , older FFx; ten times quicker !! One orbit in about 6s.

I'll have to look into what is wrong with the desktop PC's firefox.
 
Last edited:

tony873004

Science Advisor
Gold Member
1,749
141
The sim you provided shows target body : Earth and barycentre is checked
That checkbox is only for the display. Now that you've got the sim running faster, you'll notice that Earth isn't stationary. It wobbles as the Moon orbits it. Uncheck the barycenter box and the the Earth will be locked to the center of the screen.
 
187
13
Thanks for the explanation.

I've realised that the peak shift is probably due to the non integer days of print out. I've just got a new JPL sequence using 399 ref frame and am doing a sim run with 128 sample step ( which is an integer submulitiple of 86400 ) , using the 'per iteration 'option rather than 'per update'. The non interger steps would also occasionally skip a day which would broaden the peaks. It should be more consistent this time.

Hopefully this will give apples to apples comparison.

OK, you will pleased to hear it is damn near identical to JPL output, to judge by visual inspection. I'll post if I see anything in the spectra but I doubt it.
 
Last edited:
187
13
OK, I have got oeECC for the moon from JPL and done a frequency analysis. It is dominated by two peaks 31.8122 and 205.888 days.

The latter is due to the alignment of the lunar apside ( or its major axis ) with the earth-sun direction. It is half that period since alignments at either end of the ellipse have very similar effects. The first figure is the temporal coincidence of the new moon ( syzygy ) and the 205.9d cycle :

1/(1/31.8122 -1/29.5305888 ) = 411.74 = 1/(1/365.25 -1/3232. )

So the variability is fundamentally solar and due to the obvious alignments.
That gives quite a lot on insight about the variations but does not provide an analytic description of the underlying torque that produces the steady net precession.

That's what I was looking for with the original question, but maybe this is not the right place to get such a technical explanation.



There are some also-rans at 27.5546, 365.2, 411.6 , 1094.20 (2.996a),
14.7645 = 29.53/2 , though no 29.53
a couple of small peaks that appear to be sub-multiples ( odd harmonics ) of 2 years:
31.8119 = 365.25/11.48 = 2a / 22.96
34.8474 = 365.25/10.48 = 2a / 20.96

So most of the change in eccentricity is due to the sun elongating the orbit when its long axis aligns with the sun. It is interesting to note how the periods get changed.

I would not have associated 31.81d with any lunar period.

plus
37.63d and 9.61d ( which I can't see any reason for ).
 
Last edited:

Related Threads for: What is the cause of variations in lunar eccentricity?

Replies
3
Views
6K
Replies
35
Views
9K
  • Posted
Replies
0
Views
1K
Replies
3
Views
3K
Replies
19
Views
6K
Replies
10
Views
3K
Replies
16
Views
6K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top