Solstices and equinoxes: astronomy, 2026-2027 dates and history
Solstices and equinoxes explained simply: Earth's tilt, unequal seasons, length of the day, exact dates in 2026 and 2027, ancient festivals and the wheel of the year.
Key points
| Cause of the seasons | The tilt of Earth's axis, about 23.44 degrees, and not the distance to the Sun |
|---|---|
| Solstices | Moments when the Sun is at its furthest north or south: around 21 June and 21 December |
| Equinoxes | Moments when the Sun is directly over the equator: around 20 March and 23 September |
| 2026 | 20 March, 21 June, 23 September, 21 December (times in the table below) |
| Length of the seasons in 2026 | Spring 92.7 days; summer 93.7 days; autumn 89.9 days; winter 89.0 days |
| Southern hemisphere | Seasons reversed: the June solstice there is the winter solstice |
What a solstice and an equinox are
A solstice is the moment when the Sun reaches its northernmost point (around 21 June) or its southernmost point (around 21 December) relative to the celestial equator. The word comes from Latin sol (the Sun) and sistere (to stand still): for a few days, its height at noon seems not to change. An equinox is the moment when the Sun passes exactly overhead the Earth's equator (around 20 March and 22 or 23 September). These are therefore precise instants, given to the minute, and not whole days, even though everyday usage speaks of the “equinox day”.
These four moments divide the year into four astronomical seasons. Astronomy and meteorology do not use the same division: in meteorology, the seasons begin on 1 March, 1 June, 1 September and 1 December, which makes statistics easier.
Why the seasons exist
The cause of the seasons is the tilt of Earth's axis, about 23.44 degrees relative to the plane of its orbit. When the northern hemisphere leans towards the Sun, the rays arrive more vertically, the days are long and the heat received increases: that is summer. Six months later, it is the reverse. Distance from the Sun has nothing to do with it: Earth is closest to the Sun (perihelion) around 3 January, in the depths of the northern winter, and farthest (aphelion) around 5 July. The difference in distance is about 3%.
In the southern hemisphere, everything is reversed: the June solstice is the winter solstice, and the December one is the summer solstice. Neopagans in the southern hemisphere, moreover, shift their festivals by six months.
The exact dates in 2026 and 2027
These moments do not fall at the same time, nor always on the same day. Here are our values for mainland France (Paris legal time), calculated with Jean Meeus's formulas and compared with those of Wikipedia (a difference of one minute):
| Moment | 2026 | 2027 |
|---|---|---|
| March equinox | 20 March, 3:45 p.m. | 20 March, 9:24 p.m. |
| June solstice | 21 June, 10:24 a.m. | 21 June, 4:10 p.m. |
| September equinox | 23 September, 2:05 a.m. | 23 September, 8:01 a.m. |
| December solstice | 21 December, 9:50 p.m. | 22 December, 3:42 a.m. |
Check these values against an official ephemeris (IMCCE, Paris Observatory) before using them to organise a ceremony.
Seasons of unequal length
The four seasons are not all the same length. Earth's orbit is an ellipse, and Earth moves faster when it is closer to the Sun. As a result, in the northern hemisphere, summer is the longest season and winter the shortest.
| Astronomical season (northern hemisphere) | Length in 2026 |
|---|---|
| Spring (20 March–21 June) | 92.7 days |
| Summer (21 June–23 September) | 93.7 days |
| Autumn (23 September–21 December) | 89.9 days |
| Winter (21 December–20 March 2027) | 89.0 days |
Another consequence: the mid-season points do not fall on the traditional dates. The four astronomical mid-seasons of 2026 are around 4 February, 5 May, 7 August and 6 November, whereas the festivals of Imbolc, Beltane, Lughnasadh and Samhain are celebrated by convention on 1 February, 1 May, 1 August and 31 October or 1 November.
The length of the day
In Paris, the day lasts about 16 hours 10 minutes at the June solstice and about 8 hours 15 minutes at the December one (calculated with standard atmospheric refraction). In Marseille, the gap is smaller (about 15 hours 25 minutes and 9 hours); in London, it is larger (about 16 hours 40 minutes and 7 hours 50 minutes). North of the Arctic Circle (66.56 degrees north latitude), the Sun does not set at the June solstice: this is the midnight sun.
The shortest day is not the one on which the sun sets earliest: at our latitudes, the earliest sunset occurs around 10 December and the latest sunrise in early January, because of the equation of time (the offset between solar noon and clock noon). Another point: at the equinox, the day lasts a little longer than the night (about 12 hours 10 minutes in Paris), because refraction raises the Sun and the upper edge of the disc is counted. The “equilux”, the day when day and night are truly equal, falls a few days before the March equinox and after the September one.
Why the dates change
The tropical year (the year of the seasons) lasts about 365.2422 days, while the Gregorian calendar averages 365.2425 days, thanks to its leap years. The drift of about a quarter of a day per year explains why the March equinox moves between 19 and 21 March in the 21st century: earliest on 19 March 2096, latest on 21 March 2003, according to Wikipedia. The equinox was long the reference point for Easter: the Julian calendar had fallen behind the Sun, and the 1582 reform under Pope Gregory XIII restored the March equinox to the date it had at the Council of Nicaea in 325.
Monuments, festivals and traditions
Solstices and equinoxes have marked peoples since prehistoric times. At Newgrange, in Ireland, a monument built around 3200 BCE, the rising sun of the winter solstice enters the chamber for about 17 minutes through an opening above the door, according to the Irish Office of Public Works. At Stonehenge, in England, the main axis is aligned with the sunrise at the summer solstice (and the sunset at the winter solstice), according to most archaeologists. The Iranian calendar begins at the March equinox (Norouz). In East Asia, the Dongzhi festival marks the winter solstice. Among the Aymara, the New Year is celebrated around 21 June. In France, the Fête de la musique takes place on 21 June, and Saint John's Day, on the 24th, was marked by bonfires. Christmas, on 25 December, was the solstice day in the Roman calendar, which is one of the explanations proposed for this choice (see Celtic festivals and Christian festivals).
The modern “wheel of the year” makes the four solstices and equinoxes its “lesser sabbats”: Yule, Ostara, Litha and Mabon. This organisation is a 20th-century choice (see history of Wicca).
A simple and safe experiment
Plant a straight stick firmly in the ground, on flat terrain, and mark the tip of its shadow at solar noon, when it is shortest. Repeat this each season: the shadow is longest in December and shortest in June. Never look at the Sun, even through sunglasses: the shadow is enough.
Frequently asked questions
What is the difference between a solstice and an equinox?
At the solstice, the Sun is at its furthest point north or south: it is the longest or shortest day. At the equinox, it is directly over the equator: day and night are roughly equal.
Why is the equinox not always 21 March?
Because the year of the seasons does not contain a whole number of days. In the 21st century the equinox moves between 19 and 21 March.
Are day and night equal at the equinox?
Nearly. The day lasts a little longer than the night because of atmospheric refraction. Exact equality happens a few days before the March equinox and after the September one.
Why is it hotter in summer?
Because of the tilt of Earth's axis, not the distance to the Sun. Earth is even farther from the Sun in July than in January.
Are solstices Celtic festivals?
The four Irish festivals attested in the Middle Ages fall halfway between the solstices and equinoxes, not on them; the modern “lesser sabbats” date from the 20th century. Peoples of very different cultures have nonetheless marked these moments.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to The Wheel of the Year.