It is said that the earth axis changes its tilt with a period of 41 000 years. So used the image
https://upload.wikimedia.org/wikipedia/commons/1/17/Obliquity_berger_0_to_1000000.png
removed the grid so it became like this
Then I used the following script
function rasterwave(imagefile)
data=imread(imagefile);
x=[1:size(data,1)]';
X=repmat(x, 1, size(data,2));
colsum=sum(data);
y=sum(data(:, [1:size(data,2)]').*X)./colsum;
Y=abs(fft(y));
plot(Y(2:length(Y)/2), '.-')
end
To extract a spectrum (Frequency and intensity in arbitrary units):
It looks like there are two dominant frequencies in the spectrum, or maybe there is one peak followed by a band. Can these frequencies somehow be derived from the orbital periods of other planets?
Update:
Since the original image marks the timescale, it is actually possible to compute a sample rate, and plot the period on the x axis:
function rasterwave(imagefile, max_duration)
data=imread(imagefile);
x=[1:size(data,1)]';
X=repmat(x, 1, size(data,2));
colsum=sum(data);
y=sum(data(:, [1:size(data,2)]').*X)./colsum;
Y=abs(fft(y));
fs=length(Y)/max_duration;
f=linspace(0, fs, length(Y));
plot(1.0./f(2:length(f)/2), Y(2:length(Y)/2), '.-')
end
Now we see the 41 000 year period together with some 53 000 year cycle.