Solstice
A solstice is one of the two yearly moments when the Sun reaches its greatest north or south position in the sky.
What a solstice is
A solstice is a precise moment when the Sun's apparent path reaches its farthest north or south point in the sky. It happens twice each year because Earth's axis is tilted as the planet orbits the Sun. The word is also used for the calendar date near that moment.
June and December
The June solstice occurs when the Sun is farthest north on the celestial sphere. It is the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. The December solstice reverses the pattern: the Sun is farthest south, giving the Northern Hemisphere winter and the Southern Hemisphere summer.
Why solstices happen
Earth's rotation axis is tilted relative to the plane of its orbit. As Earth travels around the Sun, one hemisphere leans more toward the Sun for part of the year and more away from it six months later. Solstices are the endpoints of that yearly swing in sunlight angle and day length.
Longest and shortest days
Near a summer solstice, daylight lasts longer and the Sun takes a higher path across the sky. Near a winter solstice, daylight is shorter and the Sun stays lower. The exact daylight length depends strongly on latitude: polar regions can have 24-hour daylight or darkness around a solstice.
The Sun seems to stand still
The name solstice comes from the impression that the Sun's north-south motion pauses before reversing. Around the solstice, the Sun's daily rising and setting positions change only slowly. The pause is apparent rather than literal, but it is noticeable to careful skywatchers.
Solstice and the ecliptic
In celestial-coordinate language, solstices occur where the Sun's position along the ecliptic reaches the greatest angular distance from the celestial equator. The ecliptic is tilted relative to the celestial equator, so the Sun's apparent path can move north and south through the year.
Calendars and culture
Solstices have long mattered to calendars, monuments, festivals, agriculture, and navigation. Sites such as Stonehenge are often discussed because of their alignments with solstice sunrise or sunset. Cultural meanings vary, but the sky event is the same: a seasonal extreme in the Sun's apparent path.
Why it matters
Solstices connect Earth's axial tilt to everyday experience. They explain extreme day lengths, anchor astronomical seasons, help people understand solar paths, and give calendars a visible link to the geometry of Earth and Sun.