Solstice Calculator

A solstice is one of the two moments each year when Earth's rotational axis is tilted most directly toward or away from the Sun, causing that hemisphere to experience its longest or shortest day of the year. The word comes from the Latin solstitium — sol (sun) + sistere (to stop) — referring to the sun's apparent pause at its extreme northern or southern position before reversing direction.

The June solstice (typically June 20–21) marks the moment when the Northern Hemisphere is tilted most directly toward the Sun. The North Pole experiences 24 hours of sunlight; locations above the Arctic Circle (66.5°N) see the midnight sun. For the Northern Hemisphere, this is the summer solstice — the longest day of the year. For the Southern Hemisphere, it is the winter solstice.

The December solstice (typically December 21–22) is the reverse: the Southern Hemisphere tilts toward the Sun, creating the Northern Hemisphere's winter solstice (shortest day) and the Southern Hemisphere's summer solstice (longest day). The South Pole experiences continuous sunlight while regions north of the Arctic Circle are in polar night.

This calculator uses the Meeus polynomial algorithm to compute precise Julian Day Ephemeris (JDE) values for both solstices in any year from 1 CE to 9999, then converts to Gregorian calendar dates and UTC times.

The solstice dates are computed using polynomial expressions that approximate the Julian Day of each solstice, based on Jean Meeus's Astronomical Algorithms.

The four astronomical seasons are defined by the equinoxes and solstices, but they are not equal in length. Earth moves faster through its orbit when closer to the Sun (perihelion, early January) and slower when farther away (aphelion, early July). This causes Northern Hemisphere summer (spring equinox to autumn equinox, ~186 days) to be longer than Northern Hemisphere winter (~179 days).

1. Enter a Year: Type any year from 1 to 9999.
2. View Solstice Dates: Both the June and December solstice dates are shown with their exact UTC times.
3. Use Navigation: Previous/Next buttons step through years for quick multi-year comparison.

Solstices have been central to human culture for millennia. Stonehenge is precisely aligned with the midsummer sunrise; Newgrange in Ireland with the midwinter sunrise. The ancient Egyptians, Maya, Inca, Chinese, and virtually every agricultural civilization marked solstices with festivals, rituals, and calendrical records because they provided reliable anchors for planting and harvest seasons.

In solar energy engineering, the December solstice determines the worst-case solar angle for Northern Hemisphere installations — the day with the lowest sun angle and minimum energy collection. Solar panel tilt angles and seasonal energy forecasts are calculated from solstice geometry.

The June solstice marks the beginning of astronomical summer and the Persian New Year in some traditional calendars. The December solstice is the astronomical beginning of winter and influenced the placement of Christmas and many mid-winter festivals across cultures.