The sun's rays reach their maximum straightness so the Irradiation solar we receive is maximum. ● The Declination is minimal. ● It is the longest day of the year.
On the equinoxes
The Irradiation is average. ● The Declination is zero. ● Day and night last the same (12 hours).
At the Wintersolstice (northern hemisphere).
The sun's rays reach their maximum obliquity so the solar irradiation we receive is minimal. ● The Declination is maximum. ● It is the shortest day of the year.
Notes:
The light received in the temperate zones is highlighted to make the irradiation difference between hemispheres in each case more evident.
The Declination is the angle formed by the Sun-Earth line and the plane that contains the equator.
The Sun-Earth Line is the imaginary line that joins the centers of the Sun and Earth.
The Irradiation is the amount of light that we receive per unit of surface.
Paradox: In the northern hemisphere it is summer when the Earth is farthest from the Sun and vice versa.