Solstice corresponds to two days of the year when the inequality between day and night is maximum. One is in June and the other in December. These two days also mark the beginning of two seasons, summer and winter. The first day of summer will be the longest day and the first day of winter will be the shortest day.

It should be noted that this is reversed in both hemispheres. Thus the June solstice will be the longest day in the northern hemisphere and the first day of summer in this hemisphere, but for the southern hemisphere the June solstice will be the shortest day and thus the first day of winter. This will be reversed for the December solstice.

The closer we get to the equator, the more the variations of days and nights are attenuated to finally have all year long only equinoxes at the level of the equator where the climate will also be almost always the same throughout the year.