Reading this Wikipedia article and following the derivations (https://en.wikipedia.org/wiki/Solar_irradiance#Milankovitch_cycles), I have found an equation I can't see where it comes from. Perhaps it's simple but my positional astronomy is on its basics.
It says that if $\theta$ the conventional polar angle describing a planetary orbit ($\theta = 0$ at the vernal equinox), $\epsilon$ is the obliquity, the declination $\delta$ as function of the orbital position is $\delta = \epsilon \sin\theta$.
Could you please explain or point to some resource? Thx.