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Column When does spring really start? Let's clear this is up once and for all.

Is spring the start of February… or the start of March? If you ask me, there’s only one proper answer, and it involves astronomy. But there are a couple of reasons behind different dates, writes Conor Farrell.

IF YOU’RE ONE of those charlatans who thinks it starts in March, I can only assume you are generally untrustworthy and probably like Barry’s Tea.

But really. What qualifies as the ‘first day’ of spring can often be a point of argument between people. Is it the start of February? Or the start of March? If you ask me, there’s only one proper answer, and it involves astronomy. But there are a couple of different reasons behind different dates.

When does Midsummer’s Day fall? I’ll give you a hint: it’s not in the middle of spring, autumn, or winter. Midsummer’s Day is based around the summer solstice, the longest day of the year. As Midsummer’s Day and the solstice fall in the middle of summer, and because each season lasts three months, we can deduce that summer lasts from 1.5 months before to 1.5 months after Midsummer’s Day/solstice.

The summer solstice in the Northern Hemisphere occurs around 21 June, and is opposed by the winter solstice, which takes place in December (again, usually the 21st, six months later). So, if the summer begins one and a half months before this, then we find that summer begins about a week into May, in astronomical terms. We know that each season lasts three months, so therefore, spring starts at the beginning of February.

The year and its seasons can be divided out along a circle, which resembles the Earth’s orbit around the Sun. Earth’s rotational axis is tilted slightly, so the point where the northern hemisphere is tilted most towards the Sun is the summer solstice, and where it’s tilted away is the winter solstice.

image

The Quarter days, from NASA

So why do some people say that spring starts in March?

The above diagram shows the quarter days (two solstices and two equinoxes) as positions of the Earth along its orbit around the Sun. Four more points – each located halfway between each Earth in the diagram – are called cross-quarter days, and were particularly important in pre-Christian and Celtic Ireland. If the Quarter days above marked the middle of the season, then the cross-quarter days marked the beginning of the season.

It makes astronomical sense to use the equinoxes and solstices as markers for the middle of the seasons, as it means that spring and autumn will receive the same amount of solar radiation over three months, where summer and winter will be “opposite”, each one receiving a maximum or minimum of solar radiation. It’s nice and symmetric, and symmetry is good in science.

So why do some people say that spring starts in March? This is where meteorology comes in. Because of the way climate works, weather and temperature experiences a ‘lag’ of about six weeks. This means that the three warmest months of the year, ie meteorological summer, arrive about six weeks after astronomical summer.

imageAverage temperatures, from Met Éireann

As you can see above, the warmest months from a meteorological perspective are June, July, and August, whereas we have found earlier that maximum solar radiation from the Sun occurs on May, June, and July.

There you have it. If you’re a meteorologist, spring begins on 1 March. If you’re an astronomer, it’s 1 February (or a week-ish later if you’re particularly pedantic). I’m an astronomer, so I have no doubt that spring has well and truly sprung and the lambs are frolicking in the fields as we speak. Ahem.

Conor Farrell is an avid science enthusiast and studied physics with astronomy at Dublin City University. He now works with Astronomy Ireland to promote all things space-related to a wider audience. In his spare time he writes about science and current affairs, and can be followed on Twitter at @conorsthoughts. Read more of Conor’s columns here.

Read: 6 Irish things you’ll see the minute spring arrives

Space: Ashes to Ashes, Stardust to Stardust

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    Mute Gowanoutathat
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    Feb 18th 2014, 11:19 PM

    Jazuz journal! You’re makin it out to be a very sinister .”body found in car”

    The lad died when his jeep left the road this afternoon .

    RiP

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    Mute The Polar Bear
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    Feb 18th 2014, 11:58 PM

    You read what you wanted to read in tha headline

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    Mute pat James buchannan
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    Feb 19th 2014, 3:31 AM

    “30 men with large crowd of followers kicked pigs liver for over an hour “……. Real headline …….. Football game on down the road

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    Mute Kieran Monaghan
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    Feb 19th 2014, 5:11 AM

    A pigs bladder works better than a pigs liver.

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    Mute pat James buchannan
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    Feb 19th 2014, 5:53 AM

    It was a test to see who actually reads the comments …. First used in ireland and the captains son in Co Tipp brought the idea back to England , and william Ellis wrote the rules even though we we using it for a thousand years playing a different game

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    Mute pat James buchannan
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    Feb 19th 2014, 5:58 AM

    And lived in a then village called Rugby if only had stayed in his post it would still be called Gaelic football and ball could go forward …….. Love both games and never miss one

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    Mute pat James buchannan
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    Feb 19th 2014, 6:45 AM

    And in the USA they still call on the “pigskin”

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    Mute pat James buchannan
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    Feb 19th 2014, 6:46 AM

    On = it

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    Mute pat James buchannan
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    Feb 20th 2014, 7:36 AM

    Come on Michelle …… Why did you pull my comment ?…… It was green thumbed at over 20 /1 , which means the public liked it …… Is it not the job of a journalist to let everyone have their say ….. We can stop clicking on your stories and see where it ends too.

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    Mute Butter bean
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    Feb 18th 2014, 11:32 PM

    Journal is really going down the toilet with this click bait type of story.
    May the man who lost his life rest in peace.

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    Mute Joan Featherstone
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    Feb 19th 2014, 7:08 AM

    Agree Butter Bean, theJournal started out great, but seems to have descended into Daily Mail status, this headline being a prime example. Pity. RIP to this road traffic victim.

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    Mute Eileen Rushe
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    Feb 18th 2014, 11:16 PM

    Rip thoughts are with his family

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    Mute Dave Dson
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    Feb 19th 2014, 12:28 AM

    The headline is a terrible abuse of the English language.
    RiP to the poor man.

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    Mute Angela Barrett
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    Feb 19th 2014, 12:30 AM

    Dont bother commenting much anymore because of above reasons. Used to enjoy journal. Now it annoys me. No need whatso ever to have a headline like that. Rip to the poor man and condolences to his family.

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    Mute Colin Howell
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    Feb 19th 2014, 5:58 PM
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