Seasons Calculator
When the equinoxes and solstices actually fall — to the minute, in your time zone.
How it works
The equinoxes and solstices are computed from the Sun's apparent position using the periodic terms in Meeus's Astronomical Algorithms, with a correction for the difference between dynamical time and universal time. That gives the instant each season begins to within about a minute.
An equinox is the moment the Sun crosses the celestial equator, when day and night are close to equal everywhere. A solstice is the moment it reaches its greatest declination north or south, giving the longest and shortest days. All four are instants rather than days, which is why the calendar date they fall on depends on your time zone and why published dates differ by a day between sources.
The dates drift because the tropical year is roughly 365.2422 days. Each equinox falls about six hours later than the previous one until a leap day pulls it back, which is why the March equinox moves between the 19th and the 21st.
These are astronomical seasons. Meteorological seasons begin on the first of March, June, September and December, keeping whole months together so climate records compare cleanly — a different convention rather than a competing answer.
Examples
This year's dates. The equinoxes and solstices are listed with the exact instant, so you can see which calendar date they fall on in your own zone.
Why the date moves. The tropical year is not a whole number of days, so the March equinox drifts between the 19th and the 21st and is pulled back by leap years.
The southern hemisphere. The June solstice is the longest day in Oslo and the shortest in Sydney — one instant, opposite meanings.
Practical notes
These are astronomical seasons, defined by the equinoxes and solstices — the instants the sun crosses the celestial equator or reaches its extreme declination. Meteorological seasons are different: they start on the first of March, June, September and December, which keeps whole months together for statistical purposes.
Because they are instants, the calendar date depends on your zone. An equinox late on the 20th in one place is the 21st in another, which is why published dates differ by a day between sources.
The seasons are reversed in the southern hemisphere: the June solstice is midwinter in Sydney and midsummer in Oslo. The same instant, opposite meaning.
Frequently asked questions
Why does the solstice change date each year?
A tropical year is about 365.2422 days, so the event slips roughly six hours later each year until a leap day resets it. That drift is what moves the date between the 20th and the 21st.
Are the seasons the same length?
No. Earth's orbit is elliptical and it moves faster when closer to the sun, so the period after the December solstice is the shortest by several days. The table shows the length of each.
Is the first day of spring the equinox?
Astronomically yes; meteorologically no. Meteorological spring starts on 1 March in the northern hemisphere so that seasons align with whole months.
Why does the equinox date change from year to year?
The tropical year is about a quarter of a day longer than 365 days, so each equinox falls roughly six hours later than the last until a leap day pulls it back.
Are meteorological seasons different?
Yes. They begin on the first of March, June, September and December, keeping whole months together so that climate statistics compare like with like.
Is the solstice the hottest day of the year?
No. The solstice is the longest day, but land and sea keep absorbing heat for weeks afterwards, so peak temperatures usually lag it by a month or more.
Which season is it in the southern hemisphere?
The opposite one. The June solstice is midsummer in Europe and midwinter in Australia — the same instant, reversed meaning.
Why are the seasons not equal in length?
Because the Earth's orbit is elliptical and its speed varies. Northern summer runs a few days longer than northern winter.
Why is the first day of spring not fixed?
Because the equinox is an instant determined by the Earth's orbit, not by the calendar. It drifts between the 19th and 21st of March and is pulled back by leap years.
Do the equinoxes have exactly equal day and night?
Not quite. Refraction and the fact that sunrise is measured to the sun's upper edge add several minutes of daylight, so equal day and night falls a few days either side of the equinox itself.
When does astronomical summer actually begin?
At the June solstice in the northern hemisphere and the December solstice in the southern. Meteorological summer starts weeks earlier, on the first of June or December respectively.
Why are there four seasons?
Because the axial tilt produces two extremes and two midpoints in the year. Not every culture divides the year that way: several traditional calendars use six seasons, or two defined by rainfall rather than sunlight.