# WEM | Water Engineering

Applied Ecohydrology

### Sidebar

hydro:distance-sun-earth

# 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 extraterrestrial solar radiation.