Equinoxes and solstices

A year on Earth can be split into four as we complete our orbit of the Sun. Each of these are marked by an equinox or solstice.

What is the vernal (or Spring) equinox?

The vernal equinox occurs in March, and in the Northern Hemisphere this date marks the end of Winter and beginning of Spring when the days will start getting longer and the nights shorter.

When is the spring Equinox?

In 2019 the spring equinox will occur on 20 March at 9.58pm. 

What is the autumnal equinox?

The autumnal equinox occurs in September, and in the Northern Hemisphere this date marks the end of Summer and beginning of Autumn when the days will start getting shorter and the nights longer. Find out more about the autumnal equinox

When is the autumnal equinox?

In 2019 it will occur on 23 September at 7.50am

What are the solstices and equinoxes?

The Earth’s axis is tilted by 23.4 degrees and so the plane of the Earth’s equator is tilted with respect to the plane of the Earth’s orbit around the Sun – sometimes referred to as the ecliptic.

Diagram of the seasons

This means that during the Northern Hemisphere summer, the Sun illuminates the Northern Hemisphere more than the Southern Hemisphere. During this time we receive more hours of sunlight and the longest day is known as the summer solstice. During the winter, the Sun illuminates the Southern Hemisphere more than the Northern Hemisphere because the North Pole is titled away from the Sun. During this time we receive fewer hours of sunlight and the shortest day (and longest night) is known as the winter solstice.

But at two points in the year the Sun will illuminate the Northern and Southern Hemispheres equally – these are known as the equinoxes: the autumnal equinox in October and vernal equinox in March. It’s the moment in which the plane of Earth's equator passes through the centre of the Sun's disk or the moment that the Sun passes the celestial equator from the Northern to the Southern Hemisphere or vice a versa. On these dates, there are approximately equal hours of daylight and darkness.

The ecliptic: the plane in which the Earth and most of the other planets orbit around the Sun over a year.

The celestial equator: an imaginary projection of the Earth's equator onto the sky.

Image of equinox diagram
Creative Commons - Earth lighting equinox

When do the equinoxes occur?

The table below shows the dates and times of both the vernal (spring) and autumnal equinoxes:


Vernal equinox

Autumnal equinox

Leap year


20 March, 9.58pm

23 September, 7.50am



20 March, 3.50am

22 September, 1.31pm


All times are UTC (GMT)

What is the winter solstice?

The winter solstice occurs in December and marks midwinter with the shortest day and longest night. Find out more about the winter solstice

In 2019 it will occur on 22 December

What is the summer solstice?

The summer solstice occurs in June and marks midsummer with the longest day and shortest night.

In 2019 it will occur on 21 June

When do the solstices occur?

The times when the Sun is at its furthest from the celestial equator are called the summer and winter solstices. These occur at midsummer and midwinter.

The world 'solstice' comes from the Latin solstitium meaning 'Sun stands still', because the apparent movement of the Sun's path north or south stops before changing direction.




Leap year


21 June, 3.54pm

22 December, 4.19am



20 June, 9.44pm

21 December, 10.02am


All times are UTC (GMT)

Where does the word 'equinox' come from?

The word equinox comes from the Latin aequinoctium meaning 'equal night'.

Where does the word 'solstice' come from?

The world 'solstice' comes from the Latin solstitium meaning 'Sun stands still' because the apparent movement of the Sun's path north or south stops before changing direction.

Why don't the solstices and equinoxes occur on the same days annually?

The Earth takes approximately 365¼ days to go around the Sun. This is why we have a leap year every four years to add another day to our calendar; and so that there is not a gradual drift of date through the seasons.

For the same reason the precise time of the equinoxes are not the same each year, and generally will occur about six hours later each year, with a jump of a day (backwards) on leap years.

The path of the sun

Kelly Barfoot explains how the solstices inspired her photo, 'Solargraph – Newton’s Apple Tree'. Her image was shortlisted in the Insight Astronomy Photographer of the Year Award 2017

Find out more about the largest international competition of its kind

Image of path of sun with Newton's apple tree
Solargraph – Newton’s Apple Tree (c) Kelly Barfoot | Our Sun, Insight Astronomy Photographer of the Year Award 2017

“This is a solargraph image of Sir Isaac Newton’s apple tree at Woolsthorpe Manor, Lincolnshire, where many of his great discoveries were made.

The aim was to capture the path of the sun each day between the winter and summer solstices. As the photographic exposure of six months was so long, the result was not processed using usual dark room methods, instead it was processed digitally." - Kelly Barfoot

What is the difference between Midsummer Day and the summer solstice?

Midsummer Day occurs annually on 24 June and is one of the four Quarter Days in the UK Legal Calendar. The other Quarter Days are Lady Day (25 March), Michaelmas (29 September) and Christmas Day (25 December).

The Royal Observatory is open daily from 10am.

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