It's time to pack away your jumpers and gloves – spring has officially sprung across the Northern Hemisphere. At precisely 14:46 GMT today, the vernal equinox occurred, marking the exact moment when the centre of the sun crossed the plane of Earth's equator.
What is the Vernal Equinox?
The vernal equinox – from Latin, meaning equal (equi) night (nox) – happens twice every year. In 2026, the equinoxes will occur on 20 March at exactly 14:46 UTC, and again on 23 September, at 00:05 UTC. This event signals the astronomical start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
How the Equinox Changes Our Skies
From today, observers anywhere on Earth will see the sun's path in the sky continue its movement further north every day. That will last until the summer solstice on 21 June, after which the sun begins travelling south. During the equinox, the sun shines equally on both the Northern and Southern Hemispheres.
For this reason, it's the only time of the year when the North and South Poles are simultaneously lit by sunlight!
NASA Explains the Seasonal Shift
'Equinoxes are associated with the changing seasons,' NASA explained. 'In March, Northern Hemisphere observers welcome the longer, warmer days heralded by their vernal, or spring, equinox. But Southern Hemisphere observers note the shorter days – and longer, cooler nights – signaled by their autumnal, or fall, equinox. Come September, the reverse is true.'
The Complication of Equal Day and Night
While you might assume that the length of day and night on the equinox is equal, this isn't actually the case. 'The date for that split depends on your latitude, and may occur a few days earlier or later than the equinox itself,' NASA explained. 'The complicating factors? Our Sun and atmosphere!'
Our sun is a sphere and not a point light source, which means its edge is refracted by our atmosphere as it rises and sets. This adds several minutes of light to every day. 'The Sun doesn't neatly wink on and off at sunrise and sunset like a light bulb, and so there isn't a perfect split of day and night on the equinox – but it's very close,' NASA added.
Meteorological vs Astronomical Spring
Some of you might be reading this story slightly confused, having thought that spring has already sprung. Well, it already has – that is, if you go by the meteorological definition. Rather than using the equinoxes, this method divides the year into four fixed seasons, each lasting three months, making it easier to track weather patterns and compare statistics.
'In the UK, meteorological spring always begins on 1 March and ends on 31 May,' the Met Office explains.
When Does Spring Start?
How the first day of spring is defined depends on whether you are referring to astronomical or meteorological spring.
Meteorological Spring
In the UK, meteorological spring always begins on 1 March and ends on 31 May. This method divides the year into four fixed seasons, each lasting three months, making it easier to track weather patterns and compare statistics.
Astronomical Spring
Astronomical spring starts on the vernal equinox, around 20 March in the Northern Hemisphere, when day and night are roughly equal in length. The exact dates can vary each year due to the Earth’s tilt and orbit around the Sun.
Source: Met Office
