The Earth axis changes tilt with a period of 41 000 years, and with an amplitude of 1.2 degrees. What does the spectrum look like? Is it a steady periodic motion, or rather some quasi-periodic phenomenon?
To clarify, I want information about frequency content of plots like this one:
Source: Wikipedia
The frequencies of orbital parameters are available directly from tables in the reference given on your wiki link
See:
https://journals.ametsoc.org/view/journals/atsc/35/12/1520-0469_1978_035_2362_ltvodi_2_0_co_2.xml
These values are sufficient for looking back 1-5M years
It's generally a combination of dominant fixed frequencies and then split frequencies, (ie. cos(a+delta) + cos(a-delta)). And then there is a long tail of smaller amplitude frequencies
Trying to go from the time domain to frequencies with things like Fourier Transform will give you artifacts (as your sampling window can't really be a multiple of all the frequencies of interest) - so avoid doing that :)
More info is available here: https://paleodyn.uni-bremen.de/gl/tmp/Orbital.html
If you want to look further back in time, then you need to use other more advanced systems b/c it needs to account for things like the mass of icesheets (mass moving poleward) and other details. Small errors over millions of years (and thousands of cycles) will lead to large errors
http://vo.imcce.fr/insola/earth/online/earth/online/index.php
But at those time scales you in effect have some frequency modulation going on, and looking at the spectrum won't make much sense
