The Shadow Rule
It is a grey morning on school sports day and every parent has decided sunscreen is for sunny days. The school's assistant disagrees, and has only a ruler's worth of arithmetic and a shadow to argue with. A short story about cloud, midsummer sun at 52 degrees north, and how much of a bottle actually gets on a child.
Mairéad Foley had four hundred paper cups, forty-two sets of egg-and-spoon, and a sky the colour of a wet slate, and she was not in the mood.
"The forecast says dry," said the school assistant, from the tablet taped to the side of the tea urn. "It says cloud until two."
"Good. Then nobody needs the lotion." She had a clipboard under one arm and a crate of bibs under the other. Half the parents had written the same thing on the permission slip, in the same tone, in the box marked sun protection: Not needed, it's overcast. One had underlined it.
"May I say something about that, before the first race?"
"If it's quick."
"The cloud and the sun are two different questions," said the assistant. "I would like to check the second one with you, and it needs a child and ten seconds."
It asked her to send out the smallest Junior Infant, which was Oisín Kavanagh, who was five and a metre and a bit tall and was at that moment trying to eat a cone from the cone-and-bean-bag course. It asked Mairéad to stand him on the tarmac, face the way the light was coming, and look at his shadow.
There was a shadow. It was faint, but it was there, a soft grey smear, and it ran out behind Oisín for about half his own height.
"Shorter than he is," said Mairéad.
"Yes. That is the whole rule. When your shadow is shorter than you are, the sun is more than forty-five degrees up the sky, and in Ireland that is the time of day when the burning part of the sunlight, the ultraviolet, is strong enough to matter. When the shadow is longer than you, the sun is low and most of that light is spent getting through the air to you. It is not exact. It is a rule for a school yard."
"It's cloudy."
"It is. I have looked at the cloud, as far as I can from a tablet in a kitchen. This morning it is thin and broken, and some of the sky is brighter than the rest, which is why Oisín has a shadow at all. Thin cloud lets through a great deal of ultraviolet. I have seen figures of more than half for light cloud and a good deal less for heavy, dark cloud, and I do not trust any figure to better than a rough sense. What I do trust is that you cannot feel it. Ultraviolet is not heat. The warm on your face is another kind of light. On a cool grey day you stay out longer because you feel fine, and the burn arrives afterwards, at tea-time, when the child says her shoulders are sore."
Mairéad looked at the shadow. It did not do anything.
"So how long is the dangerous bit?"
"Today, in Dungarvan, the sun is highest at about half past one," said the assistant. "It is the thirteenth of June, nine days from the longest day. At that hour it stands about sixty-one degrees up, which puts a one-metre-twenty child's shadow at about two-thirds of a metre. The shadow is as long as the child, forty-five degrees, at about half past ten in the morning, and again at about half past four. Sports day is eleven to three."
"All of it."
"All of it, and the children are warming up from ten."
"Fine," said Mairéad. "It's cloudy, it's Ireland, it's June, and you're telling me to cover forty-two children in lotion." She said lotion the way the committee said paperwork. "They put it on at home. Nine o'clock. I know that, because I sent a note home."
"That is where I would like to be wrong," said the assistant, "and I would like you to check me, because I'm guessing. Can you ask three of them what they put on, and when, and how?"
She asked six. Oisín had a stripe on one cheek, applied by his father in the car. Two girls from Fifth had put it on at breakfast, "like, on my face", and had washed their arms since. Cian Whelan said he had put it on "in the shower", which was a thing the assistant decided to leave. One boy said his mother had said it was all right to skip it, as it was a Thursday, which seemed to be a rule of the household.
"The number on the bottle," said the assistant, when she came back. "Thirty, or fifty. It is measured in a laboratory with a thick, even layer, two milligrams to each square centimetre of skin, which is more than most of us ever spread. People who have been watched doing it put on about a half of that, or less, and a half of the amount does not give half the protection; it gives much less than half. A thirty on a thin layer is, on a bad day, nearer a five. And nine o'clock to eleven o'clock is two hours of play and a run through a hosepipe. It sweats off, and rubs off, and it is the reason the label says every two hours."
"We haven't got a budget for lotion."
"I know. The school has a shade tent, a gazebo for the hall and four sun hats left in lost property. It has the wall of the prefab on the east side, which has shade from midday. I have not got a better answer. It is not much, but it is better than the lotion alone."
"Which is what?"
"Shade for the waiting, which is most of a sports day," said the assistant. "A hat that has a brim or a flap, for anyone who has one. And lotion on the shoulders and the back of the neck, where a hat does not reach, by two o'clock, put on by an adult who can see it. A child hardly ever feels the back of their own neck. And the tent where the Infants line up, because they are the ones who will stand still."
Mairéad did not like it. She wrote the plan on the back of the clipboard, in the margin of the egg-and-spoon heats, and she said so: "I don't like it." But she wrote it.
The principal came out at ten to eleven, Mr Quinlan, in his good jacket, and stopped at the gazebo.
"Is this for the weather?"
"It's for the shadows, Seán," said Mairéad.
"There's a rule against pitching it on the track."
"It's not on the track. It's by the start."
"We'll look as if we expect rain."
"No," she said, and for the first time that morning she was not annoyed, only tired, and she realised she was about to win an argument she did not entirely believe in. "Seán. Look at the Junior Infants' shadows. I'd like you to look at them before you decide we're fools."
He looked. A line of five-year-olds stood behind a rope, in bibs, and each of them had a small grey patch on the ground at their feet, short as a dropped glove.
"I'll hold the other end of the gazebo," said Mr Quinlan.
It went well, which was the trouble with it: nothing happened. The cloud thickened at noon and thinned again by one, and the tent filled up with small people eating orange segments. At a quarter to two the assistant, which had no way to see the yard but a camera pointed at the gate, said only, "Back of the neck, please, before the relay," and Mairéad went round with a tube and a tissue, and did two dozen children in ten minutes, and was told by Cian Whelan that it was freezing.
There was a pink ear. There was one pink ear, on one boy who had been on the hill after the high jump, and who did not mind.
Late in the afternoon Mairéad stood on the empty yard with the cups in a sack and looked at her own shadow, which had lengthened, and which fell across the white lines of the track, and across the chalked circle where the egg-and-spoon heats had been. It reached the far wall.
"Four forty," said the assistant. "It's longer than you are now."
"I know," said Mairéad, and went in to ring the parents, and tell them that the permission slips were wrong, and that she was sorry, and that it was a very good rule.
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This story was written by an AI and is fiction. Scoil Naomh Eoin, Mairéad Foley, Seán Quinlan, Oisín Kavanagh and Cian Whelan are invented; County Waterford and Dungarvan are real, and no real school or person is described. The numbers are estimates for a kitchen table. At latitude about 52.1 degrees north on 13 June the sun's declination is about 23.1 degrees, so its noon elevation is 90 − 52.1 + 23.1, about 61 degrees; a shadow equals the person's height at 45 degrees, which for this place and date works out at roughly three hours either side of solar noon (taken here as about half past one in the afternoon, clock time in Ireland in summer). The shadow rule is a widely taught rule of thumb, not a measurement. How much ultraviolet light passes through cloud varies a great deal with the cloud; thin cloud can pass most of it, and the story claims no exact figure. The SPF on a bottle is measured at 2 mg of product per square centimetre; studies of real use commonly find people apply considerably less, so the protection is lower than the label; reapplying about every two hours, and after swimming or sweating, is standard advice. Sunscreen is a second line after shade, clothing and a hat. This is not medical advice; for skin that has burned badly, or a mole that changes, ask a doctor. A school sports day is ordinary school life; nothing here is Church teaching.