====== Distance Sun-Earth ======

The relative distance between sun and earth varies as a function of the Julian day $J$:

$$d_{se} = 1+0.033*cos \left ( \frac {2*\pi}{365} * J \right ) $$.

The value $d_{se}$ is needed to calculate the [[en:hydro:extraterrestrial-radiation|extraterrestrial solar radiation]].