June 21st the longest day and shortest night of the year in the Northern Hemisphere. And ut is the shortest day in the Southern Hemisphere
Why the days are longer in Northern Hemisphere and shorter in Southern Hemisphere?
On the day of the June solstice, the north pole is tipped more directly toward the sun, and the south pole is tipped more directly away from the sun. Hence the days are longer in Northern Hemisphere and shorter in Southern Hemisphere.
Interesting facts:
The word "solstice" comes from the Latin words "sol" (i.e. sun) and "sistere" (i.e. stationary).
It occurs twice a year. In the Northern Hemisphere, it happens in June and in the Southern Hemisphere, it occurs in December.