'BUSY old fool, unruly Sun,
Why dost thou thus,
Through windows, and through curtains, call on us?
Must to thy motions lovers' seasons run?'
From The Sun Rising John Donne
Today is Midsummer's Eve and for days the local newspapers have carried advertisements from country hotels inviting us to bonfire parties in their gardens. In true Scottish tradition the thunderclouds have been brooding all day but no doubt the venues are well prepared with marquees from which spectators can enjoy their rib roast and solstice-themed cocktails while staying dry.'Experience all the excitement of a real Celtic fire festival!' one advertisement enticed. I suppose in these challenging times they can't be blamed for trying but it was tempting to let them know that Midsummer bonfires have little to do with the Celts. While undoubtedly pagan, the parts of Britain with the strongest traditions of bonfires in June are Norse or Anglian, not Celtic.
So Midsummer is upon us, that curious time after the solstice when the sun, at the extreme limit of its station, appears to hover unmoving and undecided in the sky, rising and setting at almost the same time each day. It is, after all, what the word solstice means, from the Latin solstitium, or 'sun-halting'. Like its counterpart at the other end of the year, 24 June has been conveniently commandeered by the Christian calendar as the Feast of John the Baptist who, the Gospel of St Luke tells us, was born six months before Christ and 'jumped in the womb' on learning of the Virgin's conception.
At school we learned that the summer solstice occurs each 21 June and like much else we learned at school, while generally true it is not universally so. In fact the solstice may fall on 20 June (as it last did in 2008) and may be as late as 22 June (although this last occurred in 1971 and won't happen again in any of our lifetimes). This year, in Britain, it fell a little after 6.16pm on the date my school approved of, although those of us living in the northern half of the country could be forgiven for not noticing as it poured with rain and barely seemed to get light all day.
The mathematics behind the precise calculation of the solstice is complex, so perhaps my school should be excused for wanting to keep things simple. But I can't help thinking the lack of punctuality exhibited by something as big as the sun would have been a cause for some consternation among my teachers. It was hardly setting the right example!
With the mixed blessing of hindsight, it seems now that much of my schooling was a sequence of learning and unlearning in this way. We were taught absolute truths only to have them dismantled a term or two later once we were deemed ready for subtler lessons. Thus we learned that electrons orbit around the nucleus of an atom in distinct 'shells', so many electrons to each. Our calculations of valency and compound formation relied on this certainty. Well, no actually, it's not like that at all.
Anyway, I digress. To get back to the solstice, the problem (if indeed that's how we choose to see it) of the unreliable timing isn't anything to do with the sun. The Earth wobbles on its axis like a spinning top, its orbit is disturbed by the gravity of other planets and, above all, our calendar is just not clever enough. An average orbital year is 365.242199 days. Our Gregorian calendar gets as close as it can. Its sophisticated cycle of leap (intercalary) days in years divisible by four, but not if they are divisible by 100 unless they are also divisible by 400 (still with me?) is a big improvement on its Julian predecessor. But it still means we'll be about a day awry every 3,300 years. Further refinements have been proposed but never adopted, perhaps because a further consideration then comes into play, the spinning of our Earth is slowing down so days are set to get longer!