The Math Behind Our Solstice & Equinox Dates
The four turning points of the year — two solstices and two equinoxes — are precise astronomical instants, and the tool computes them to the minute without any lookup table.
Meeus's approximation
We use the method from Jean Meeus's Astronomical Algorithms: a polynomial gives the approximate instant for a given year, then a sum of 24 periodic correction terms refines it to account for the planets' gravitational tugs on Earth's orbit. The result is the exact moment the sun crosses the equator (equinox) or reaches its furthest declination (solstice), accurate to within minutes.
Shown in your time
Those instants are universal, but the tool renders them in your local time, so "the June solstice" shows when it actually happens for you. It is the same engine that powers the Moon and sun-time calculations: everything runs client-side, with no API and no tracking. For the meaning behind the dates, see our guide on solstice vs equinox.
See this year's solstices and equinoxes for your location.
Open the Sun Times tool