A solstice is an astronomical event that occurs twice a year when the Earth's axis is tilted the most toward or away from the Sun. This happens every year on June 20-21 (Northern summer solstice) and December 21-22 (Northern winter solstice) when one part of the earth tilts to receive the sun directly overhead the Tropic of Cancer and Tropic of Capricorn, respectively
When are the solstices?
The first occurs around June 20 or 21 in the Northern Hemisphere and December 22 or 23 in the Southern Hemisphere; this is called the summer solstice.
The other occurs around December 21 or 22 in the Northern Hemisphere and June 20 or 21 in the Southern Hemisphere; this is called the winter solstice.