Two solstices occur every year, one on June 21 and one on December 21. These are the two points on the ecliptic at which the distance from the celestial equator is maximized. As shown in this video , the summer solstice is the first day of summer and also the longest day of the year. This can be thought of as the day where the spot on the earth is tilted most towards the sun. Conversely, the shortest day of the year is called the winter solstice. The dates of the solstices and their seasonal names are flipped for the northern and southern hemispheres.