science

Spring does not officially arrive in the Northern Hemisphere this year until March 20 at 16.47 GMT, the Spring Equinox – but when does Spring start for you?

The Sun FINALLY came out this week. It was a long, long winter and we all needed to feel a little of its warmth. To most of us in Ireland it has been spring since the 1^st of February but this new boost has sent the conversations about spring into overdrive at the school gate. We are all more than ready to embrace it but no one wants to hear that, to some, it is not even spring yet! Here in Ireland we seem to live in a bubble when it comes to the seasons as much of the rest of the Northern Hemisphere will tell you it is not Spring until the Equinox, which this year will occur at 16.57 (GMT) on March 20th.

In Ireland spring usually means people abandon their clothing in a rapid and frenzied manner.Or, to be more accurate, it means the sighting of a lot of tee shirts and shorts and the accumulated exposure of acres of alabaster skin. It’s a wonder the glow cannot be seen from space.

A SHORT GEOGRAPHICAL LOOK AT HOW WE DEFINE SPRING

To be honest I was a little surprised to learn that most of the World is celebrating the start of a season while we Irish are smack bang in the middle of it! I took to twitter and Facebook to find out what people really thought and was delighted with the variety of responses we got.

• In Ireland we learn at school that spring starts 1^st February. Many people said the biggest problem they had with this was that it pushes August into autumn so most Irish seem to either amend the seasons to a four month summer or they mentally move the seasons on a month. We Irish are not afraid to bend the rules to suit ourselves!
• Many Irish people follow the Celtic calendar which also says spring starts on the 1st of February. This coincides with the arrival of certain seasonal plants and the spring lamb.

• Once we move outside of Ireland it would seem that the rest of the Northern Hemisphere shift the seasons on a little. Our nearest neighbours in the UK start spring on 1^st March.

• If we move further West into France and the rest of Europe it seems the Spring Equinox is generally held as the beginning of the season.

• In the USA the Spring Equinox is the official start of spring although many will hold the 1^st March as an acceptable alternative.

• My favourite response to the question of “When does spring start for you?” was this one…

 My husband says it’s Spring when we stop making stew once a week!

SOME OFFICIAL DEFINITIONS OF SPRING

The national meteorological body in Ireland defines March 1^st as the first day of spring.

The Old Farmer’s Almanac defines the spring equinox as the start of the season.

WHAT IS AN EQUINOX?

An equinox is an astronomical phenomenon – a time on Earth when we experience almost equal day and night. There are two equinoxes in our calendar year, one in March (between 19th and 21st) and one in September (between 20th and 23rd). The March one is referred to as the Spring (vernal) equinox in the Northern hemisphere and the September one is the Autumn equinox.

These are reversed in the Southern hemisphere.

The word Equinox literally means equal night derived from the Latin words “equi” (equal) and “nox” (night).

HOW DOES IT WORK EXACTLY?

The equinox refers to a time when there is almost equal day and night in most parts of the World. On the Equinox the centre of the Sun will be directly above the Earth’s equator at noon.

The Northern and Southern hemispheres will be equally illuminates at this moment. http://en.wikipedia.org/wiki/Equinox

A LITTLE MORE DETAIL…

To better understand the seasons we need to look at the movement of the Earth within its celestial space.

Firstly, the Earth rotates on its own (Polar) axis every 24 hours. Thus different parts of the Earth are facing towards the Sun at different stages of the day – this is what makes day and night.

The Earth also travels around the Sun once every 365.25 days (or 365.24219 days to be more exact) – that explains a complete year on Earth.

I hope all this isn’t making you dizzy as there is a third factor to take into account and this is the factor that accounts for the seasons; The Earth is actually tilted on its own axis by 23.5 degrees. This tilt remains constant as the Earth orbits the Sun. Therefore at different times during this orbit the Northern or Southern hemispheres will gain more Sunlight as they are tilted more towards the Sun.

The Equinoxes (Spring and Autumnal) are the only times during the year when the Earth’s 23.5 degree axis is not tilted towards or away from the Sun. At these times in the year the Sun sits exactly over the equator.

WHY DOES THE EXACT TIME OF THE EQUINOX DIFFER EACH YEAR?

Our year is governed by how long it takes the Earth to orbit the Sun. By the Gregorian calendar there are 365 days in a year. However this is not quite true as mentioned above, a year is actually 365.25 days in length (the actual duration of a full orbit of the Sun by the Earth). We fix the error by adding a Leap Year in every four years.

This does not completely fix the timing for the equinoxes however which will occur six hours later every year. The Gregorian calendar does manage to confine the timing of the equinox to within the same few days. By this calendar the equinox will occur at the exact same time every 400 years.

SOME COOL PLACES TO BE ON THE EQUINOX…

If you are standing at the North Pole on the Spring Equinox you will see the Sun start to peep over the horizon, signalling the end of six months or darkness and marking the start of six months of daylight.

If you are standing at the South Pole on the Spring Equinox the opposite is true.

If you are standing on the Equator at noon on the Equinox you will observe the Sun exactly overhead.

WHAT DOES MOTHER NATURE HAVE TO SAY ABOUT ALL THIS?

If, like me you find this scientific definition of spring hard to take in, don’t worry, Nature seems to have its own definition of spring. I do not think the emerging buds or the territorial birds are too bothered about when the Sun might sit exactly over the Equator.

To them spring is in full throttle and to me it is too!

So what is your definition of spring?