At the moment, night races seem to be in wax, orbiting around the running calendar in a reassuringly predictable fashion. But how much thought goes in to the cycle of the moon, when planning these events? When I started organizing night races with my second cousin Ben three years ago, we didn’t pay much heed to the moon’s influence. Watching a train of runners disappear over the horizon on Dartmoor was special enough.
Then we received an email from another organizer who likes to do things by the light of a full moon. He seemed to have a bit to say about the moon’s proper role in all of this, and so we did some research. Our correspondent turned out to be none other than Professor Emeritus of Observational Astronomy and a researcher into stellar radial velocities and binary-star orbit determination at the Institute of Astronomy, Cambridge University.
Although he’s now 79, professor Roger Griffin is a keen runner, and runs almost every day – he’s a member of the University Hare and Hounds. For several years now, he has staged a somewhat spontaneous Midnight Moonlit Meadows Run, which starts just as the moon is about to hit its highest point in the night’s sky, on the Meridian.
He even abandons his post to take part in the annual flit across Grantchester meadows to the church, starting at 23.38. No head-torches are needed, and the idea is to reach Grantchester
church, about 2.5 miles away, just in time to hear the clock strike midnight, before turning around and running for home. It is a spontaneous affair, with an email simply going out a few hours before the event to confirm proceedings.
No ordinary observer of the skies, prof Griffin makes a majority of his observations on-site with his 36 inch telescope. More binary-star orbits have been determined by him than by any other observatory in the world. So when he contacted us to suggest we stage our run two days before the full moon, we were all ears. We had hoped to stage our off-road half marathon night race, The Moonlit Flit, under the light of a full moon. But given a crowded race calendar, this isn’t always possible.
A full moon near the winter solstice, on 21 December, occupies the same place in the sky as the sun does at the summer solstice on 21 June. It is high in the sky, and is highest at midnight. In open landscapes, this is enough light to run by.
Because the full moon is roughly ten times brighter than the half phase, you can’t afford to go too far away from full if you want to have enough light to see by. At the same time you need to have it reasonably high in the sky, which means waiting until late in the evening. While midnight on the night of full moon is ideal for prof Griffin, it wasn’t right for us – it would have significantly affected turnout.
But next time, we won’t have to wait until midnight. As prof Griffin explains: “The moon moves among the stars from right to left, and the amount that it moves between one night and the next is about equivalent to how far it moves in the ordinary course of rising and setting in one hour. So the night previous to a full moon, the moon will rise about an hour before sunset, two nights previously it will rise two hours before – and so would then be at a reasonable altitude by the time the sky was dark.
“Then, you do not need to wait until it is exactly on the meridian, ie due south, where it reaches its highest altitude – it is nearly as high for the hour or two on either side of that time. On the actual night of full moon, it will be on the meridian very near midnight, but on the previous night it will reach the meridian around 11pm, and on the one before that 10pm. So it could be satisfactorily bright by about 9pm on the night before it is full and at 8pm on the night before that.
This only applies in the winter half of the year. In the summer the full moon is always low down in the sky, being in the part of the sky where the sun is in winter.
So if you come across a bunch of runners running across a field at midnight close to the solstice, you’ll know there is method to their madness.
As for prof Griffin’s motivation: An act of defiance perhaps? He told us: “I still get a kick out of organizing something that some of the young like to do but haven’t thought of organizing for themselves, whereas I am old.”
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source: The Guardian by Ceri Rees