Sun

Equinox and Solstice Dates

Exact UTC and local-time instants of the March equinox, June solstice, September equinox, and December solstice for any year from 1000 to 3000.

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Enter a year (or a range of up to 50 years), then select Calculate instants. Try This year for the current year's equinoxes and solstices.

About this calculator

Instants come from Jean Meeus, Astronomical Algorithms, chapter 27: the Table 27.B mean-instant polynomials for years 1000 to 3000, refined with the full 24-term periodic correction of Table 27.C. That series gives the moment in dynamical time (TT); Meeus quotes errors under about a minute (at most 51 seconds against numerical integration over 1951 to 2050), growing gradually toward the edges of the 1000 to 3000 range, which is why other years are not accepted. Dynamical time is converted to UTC with the Espenak and Meeus polynomial expressions for Delta T from the NASA eclipse pages, so overall accuracy is typically about one minute; all times are rounded to the nearest minute. The instants are geocentric and calendar-independent moments, the same everywhere on Earth.

Some honest caveats. Before 1972 there was no leap-second UTC, so earlier "UTC" times here really mean Universal Time (UT1, essentially Greenwich Mean Time), and for centuries far in the past Delta T itself is uncertain by minutes. For future years Delta T is a projection that can drift by tens of seconds. All dates use the proleptic Gregorian calendar, so before the 1582 calendar reform they will differ from Julian-calendar civil dates of the era. Local times use your device's time zone rules; for the September equinox especially, an instant just after midnight UTC can fall on the previous calendar date in western zones. Values compare to about a minute with published USNO and Astronomical Almanac tables, but they are approximations for planning and education, not official almanac records.