The two occasions each year when the position of the sun at a given time of day does not seem to change direction. In the Northern Hemisphere, the summer solstice occurs around June 21 and is the longest day of the year. The sun stops getting higher in the sky, and the days begin to grow shorter. The winter solstice, which occurs around December 21, is the shortest day. The sun stops getting lower in the sky, and the days begin to grow longer.