Summer solstice is the first day of summer each year and it occurs around June 21st in the Northern Hemisphere(December 21st in the Southern Hemisphere). The winter solstice is the first day of winter and occurs around December 21 in the Northern Hemisphere. (June 21 in the Southern Hemisphere).
Starting at winter solstice to summer solstice, days increase in daylight. In other words, the Sun rises earlier and sets later making the daylight period of each day longer. From summer solstice to winter solstice, days decrease in daylight. Even though the days preceding and following summer solstice (as well as the winter solstice) may all be exactly the same length, the summer solstice is the marking point for the change in daylight length and as such is called the longest day of the year. Actually, to be more scientifically correct it should be called the longest day of daylight. The same is true for the winter solstice with it being the shortest day of daylight each year.
For more information about the movements of the Earth, including rotation and revolution, and how they affect seasons, see Janice VanCleave’s Geography for Every Kid.
Geography for Every Kid
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