* Summer Solstice: This occurs when the sun reaches its highest point in the sky, resulting in the longest day of the year. It usually happens around June 20-22 in the Northern Hemisphere and December 21-23 in the Southern Hemisphere.
* Winter Solstice: This occurs when the sun reaches its lowest point in the sky, resulting in the shortest day of the year. It usually happens around December 21-23 in the Northern Hemisphere and June 20-22 in the Southern Hemisphere.
The solstices are caused by the tilt of the Earth's axis of rotation. During the summer solstice, the hemisphere tilted towards the sun experiences the longest daylight hours and the shortest nighttime hours. During the winter solstice, the opposite hemisphere is tilted away from the sun, resulting in the shortest daylight hours and the longest nighttime hours.