Whether it’s a yellow sprinkling of daffodils lining your favourite park or opening up your window for some fresh air, it’s clear that the vernal equinox - the signalling of the start of spring - has firmly arrived.
The vernal equinox, also known as the spring equinox, occurs exactly at 11.06pm eastern time on Tuesday 18 March 2024. But why do we celebrate the spring equinox?
Here’s everything you need to know about the official beginning of spring.
When is spring?
Depending on which definition of spring you use, there are two different dates that mark the first day of the season. The first day of the meteorological spring occurred at the start of the month on 1 March. However, if you go by the astronomical definition of the seasons, the first day is marked on Tuesday 19 March.
What is meteorological spring?
Meteorological seasons are based on splitting the seasons into four fixed periods, each made up of three months.
These seasons coincide with the Gregorian calendar, which is the most widely used civil calendar in the world and based on a 365-day common year divided into 12 months of irregular lengths.
Meteorological spring ends on Friday 31 May this year, preceding summer which begins on Saturday 1 June.
What is astronomical spring?
The astronomical calendar determines the seasons depending on the 23.5 degree tilt of the Earth’s rotational axis in relation to its orbit around the sun.
Astronomical spring depends on the date of the spring equinox, also known as the vernal equinox, which varies year-to-year.
The spring equinox consists of four days - two equinoxes and two solstices - during the year that mark the beginning of a new season. For the Northern Hemisphere, the spring equinox is the moment when winter ends and spring begins.
The astronomical spring will then last until the summer solstice, which this year lands on Thursday 20 June 2024 at 4.50pm eastern time.
How do the equinoxes and solstices work?
The word “equinox” derives its name from the Latin term “eqi” which means “equal” and “nox” which means “night”.
According to the astronomical calendar, there are two equinoxes each year in March and September, when the day and night are approximately 12 hours each everywhere on Earth.
This happens when the celestial equator - an imaginary projection of the Earth’s equator onto the sky - is the closest part of the Earth to the sun.
Meanwhile, the world “solstice” comes from the Latin word “solstitium” meaning “sun stands still”.
The summer and winter solstices occur when the sun is at its furthest from the celestial equator.
