Equinox and solstice calculator
Enter a year from 1900 to 2100 to get the date and time of the March equinox, June solstice, September equinox and December solstice. Times show in UTC unless you enter another time zone, and the lengths of the four seasons follow.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter a year between 1900 and 2100.
- Leave the time zone as
UTC, or enter a zone name to see local clock times.
- Read the four moments and the length of each season.
How it works
For each of the four events the tool takes the mean time from a polynomial in the year, then adds a correction made of 24 periodic terms (Meeus, chapter 27). The result is in Terrestrial Time, which is then shifted to UTC by subtracting ΔT, the difference between Terrestrial Time and Universal Time. ΔT is about 69 seconds in the 2020s.
Worked examples
- 2024: the March equinox is on 20 March at about 03:06 UTC.
- 2026: the tool gives 20 March 14:45 UTC, 21 June 08:24 UTC, 23 September 00:05 UTC and 21 December 20:50 UTC.
Good to know
An equinox or solstice is a single instant, not a whole day. In your time zone it may fall on the day before or after the UTC date.
Frequently asked questions
How accurate are the times?
The tool uses the series from Jean Meeus's Astronomical Algorithms, plus a correction for the difference between Earth's rotation time and uniform time. For recent years it should agree with published tables to about a minute or two. Future years depend on an estimate of Earth's slowing rotation.
Why does the equinox date change from year to year?
A calendar year is not a whole number of days, so the moment drifts about six hours later each year and jumps back on leap years. The March equinox falls on 19, 20 or 21 March, depending on the year and the time zone.
Are the seasons the same in the southern hemisphere?
The moments are the same worldwide, but the seasons are swapped. The March equinox starts autumn in the south, and the December solstice starts summer. The season lengths here are labelled for the northern hemisphere.
Why are the seasons different lengths?
Earth moves faster in its orbit when it is closest to the Sun, around early January, so northern winter is the shortest season and summer the longest.