Solstices

Solstices are two annual astronomical events that mark the times when the Sun reaches its greatest distance north or south of the celestial equator as seen from Earth. They correspond to the Sun's maximum or minimum apparent height in the sky at noon. The term solstice comes from Latin solstitium, from sol sun and stat- to stand, describing the moment when the Sun appears to stand still at the end of its northern or southern journey along the horizon before reversing direction.

The events are caused by the tilt of Earth's axis relative to its orbit around the Sun, about 23.44 degrees. Because of this obliquity, the Sun's declination reaches approximately +23.44 degrees at the summer solstice and −23.44 degrees at the winter solstice. In the Northern Hemisphere, the summer solstice occurs around June 20–22, producing the longest day of the year, while the winter solstice occurs around December 20–23, producing the shortest day. In the Southern Hemisphere, the seasons are opposite, so the winter solstice occurs around June 20–22, and the summer solstice around December 20–23.

The solstices influence daylight duration most strongly at northern or southern high latitudes; near the poles, they produce the midnight sun or polar night for extended periods. In most inhabited latitudes, the days around the solstices show the greatest difference in daylight compared with the equinox periods.

Culturally, solstices have long featured in calendars and festivals in many cultures, reflecting changes in day length and the turning of the year. They are related to the equinoxes, which mark equal day and night.