Spring equinox 2018: When is it, what is it and why is it important?

A guide to what the astronomical event is all about and how people around the world celebrate

It may still be frosty around the UK, but spring is officially about to start. The vernal equinox takes place tomorrow.

The astronomical event marks the start of spring in the northern hemisphere, which means longer days are on the way and people around the world will celebrate fresh starts.

When is the first day of spring?

The first day of spring in the northern hemisphere in 2018 is 20 March, according to the astronomical cycle.

This date is when day and night are around the same length, each lasting around 12 hours.

It usually takes place on 19, 20 or 21 March every year.

In the southern hemisphere, the opposite occurs, as autumn begins at the same time.

Spring starts in September south of the equator on the same day autumn starts north of the equator.

When do the clocks change?

In the UK, the clocks change soon after the start of spring.

This year they will go forward by one hour at 1am on 25 March, which is the final Sunday of the month.

This marks the start of British Summer Time – also known as Daylight Saving Time - which means there will be less sunlight in the morning and more in the evenings.

Why is it called the vernal equinox and what happens during it?

The word "vernal” comes from the Latin word for spring, while equinox literally means "equal night" (equi means equal and nox means night) as both night and day last for an equal amount of time.

Every year there are two equinoxes, one in March and another in September, the latter of which is known as the autumnal equinox.

They occur when the sun shines directly at the equator on the only day of the year the tilt of the Earth’s axis is perpendicular to the sun’s rays.

During the rest of the year, either day or night lasts a little longer, depending on where you are in the world, because of the Earth’s tilt.

This is why it starts getting darker earlier as winter progresses.

It is an event that can be contrasted with the summer and winter solstices, which happen in June and December and also mark the beginnings of new seasons.

The solstices mark the longest and shortest days of the year, which occur because the sun has reached either its highest or lowest point relative to the equator.

Astronomers use the spring equinox to measure the tropical year, which is the time it takes for the Earth to orbit the sun.

What is the meaning of the Spring Equinox and how is it celebrated around the world?

The vernal equinox marks the start of spring and a time for new beginnings, birth and fresh starts.

A number of festivals take place around this time all over the world, dating back to ancient times.

Ancient Christianity links the celebration with Easter when Jesus is believed to have died and then been reborn.

The link with the vernal equinox is clear as it coincided with pagan celebrations of rebirth and renewal.

The Mayan calendar is famed for its spring equinox rituals at the stone-stepped pyramid at Chichen Itza, Mexico.

The pyramid, where human sacrifices once took place, is made in a way that a “snake of sunlight” moves down the steps on the day of the equinox.

In Spain, the time around the start of spring has traditionally been the planting season as the ground thaws and the daylight hours become longer so crops can grow.

Japan celebrates both equinoxes with national holidays, as the days are seen as a time to worship ancestors.

The Indian tradition of bringing in spring is the festival of Holi – also known as the festival of colours.

Signifying the triumph of good over evil, people celebrate by throwing colourful powder at one another in a joyful celebration.

In Iran, the New Year begins on the day of the equinox and is marked with the festival of No Ruz.

It is all about rebirth and fresh starts so spring cleaning is done, houses are decorated and fresh flowers are gathered, before celebrating with a traditional picnic with loved ones.

In Lanark, Scotland, the start of spring is celebrated on 1 March with a festival called Whuppity Scoorie.

It involves local children running around a church swinging around paper balls on strings, before scrambling to pick up coins that are thrown down for them.