Moon Shadow

In which The Author digs out an old book

A couple of weeks ago, one of my Facebook pals shared a link about an eclipse in the UK this month. I hadn’t seen any mention of it myself, so I decided to look into it. There is in fact an eclipse due, on Friday 20 March, just two days after my birthday. I wondered why I hadn’t come across it in my old copy of The Guinness Book of Astronomy Facts and Feats (2nd edn) by Patrick Moore, published in 1979. (He was plain old ‘Mr Moore’ back then, by the way.)
The answer turned out to be more straightforward than I’d thought. Sir Patrick’s listings stopped at the total eclipse of 11 August 1999. It was logical enough, I suppose, to declare a cut-off point at the end of the century, rather than spend pages and pages listing all the forthcoming eclipses for decades to come.
Eclipses are more common than you might think. In fact, the maximum possible number in any one year is seven, made up of solar and lunar eclipses. As Sir Patrick himself pointed out, ‘in 1935 there were 5 solar and 2 lunar eclipses, and in 1982 there will be 4 solar and 3 lunar’.
Of course, whether you get to see any of them depends on a combination of factors. Your own location on the Earth’s surface is the key to how much you’ll get to witness. I vaguely remember standing in the yard of Comin School in Trecynon, looking into the sky through a piece of smoked glass. I think that must have been the partial solar eclipse of 11 May 1975, when I was nine years old.
Here in the UK we didn’t get any more Moon-on-Sun action until the summer of 1999. This was really exciting, because it would be a total eclipse – always assuming that you were right at the south-western tip of Cornwall at the time. Here in South Wales, we could look forward to about 95% totality.
Even though I knew I wouldn’t be anywhere near Lands End, I swapped a day off work (it was a Wednesday) for the occasion. I left the house in good time and took my little viewer up to the playground near the old Dare-Aman Line, where a gang of local kids had gathered to watch it for themselves. We spent our time passing the viewer around, taking turns to watch the eerie spectacle of the sun gradually being nibbled away. The birds stopped singing and it quickly became much cooler as the shadow of the moon advanced across the solar disc. I sketched out a quick diagram on a piece of paper to show what was happening, and the whole occasion turned into an impromptu science lesson.
Next Friday’s eclipse is also set for fairly early in the morning. Always assuming it doesn’t piss down, I’ll probably head for high ground and take my viewer with me again. I might even try and set up a camera obscura and photograph the solar disc at various stages. That had been my plan on the previous occasion, but it was far too breezy. We’ll have to see what happens on the day. Unlike eclipses, we still can’t predict the weather with any reasonable accuracy.
According to Sir Patrick,
The first known prediction was made by the Greek philosopher Thales, who forecast the eclipse of 25 May 585 BC. This occurred near sunset in the Mediterranean area, and is said to have put an end to a battle between the forces of King Alyattes of the Lydians and King Cyaxares of the Medes; the combatants were so alarmed by the sudden darkness that they concluded a hasty peace.
Here, for your entertainment and edification, are some more highlights from his book:
The longest possible duration of totality for a solar eclipse is 7m 31s. This has never been actually observed, but at the eclipse of 20 June 1955 totality over the Philippine Islands lasted for 7m 8s.
The shortest possible duration of totality may be a fraction of a second. This will happen at the eclipse of 3 October 1986, which will be annular among most of the central track, but will be total for about a tenth of a second over a restricted area in the North Atlantic Ocean.
The first recorded solar eclipse seems to have been that of 2136 BC (22 October), seen in China during the reign of the Emperor Chung K’ang. The Chinese believed that eclipses were due to an attack on the Sun by a hungry dragon, and they endeavoured to scare the dragon away by making as much noise as possible. (It always worked!) There is a story – probably apocryphal – that on this occasion the two Court Astronomers, Hi and Ho, were executed for their negligence in failing to predict the eclipse.
The first official American total eclipse expedition was that of 21 October 1790, when a party went to Penobscot, Maine; it was led by S. Williams of Harvard, and was given ‘free passage’ by the British forces, but unfortunately a mistake in the calculations meant that the party remained outside the track of totality!
The only emperor to have died of fright because of an eclipse was Louis of Bavaria, in 840 (his three sons then proceeded to engage in a ruinous war over the succession).
The only astronomer to have escaped from a besieged city in a balloon to study a total eclipse was Jules Janssen. The eclipse was that of 22 December 1870, and Janssen flew out of Paris, which was surrounded by the German forces. He made his way safely to Oran, but clouds prevented him from making any observations.
The longest totality ever recorded was during the eclipse of 30 June 1973. A Concorde aircraft, specially equipped for the purpose, flew underneath the Moon’s shadow and kept pace with it, so that the scientists on board (including the British astronomer John Beckman) saw a totality lasting for 72 minutes! They were carrying out observations at millimetre wavelengths, and at their height of 55 000 feet were above most of the water vapour in our atmosphere, which normally hampers such observations. They were also able to see definite changes in the corona and prominences over the full period. The Moon’s shadow moves over the Earth at over 3000 km/h.
The first attempt to show a total eclipse on television from several stations along the track was made by the BBC at the eclipse of 15 February 1961. The track passed from France into Italy and Jugoslavia, and thence into Russia. The attempt was successful; totality was shown from St Michel in France (commentator, Dr Hugh Butler); from Florence in Italy (C. A. Ronan); and from the top of Mount Jastrebec in Jugoslavia (myself). This must also have been the most peculiar way in which a television commentator has spoken to the technical crew. I talked French to a Belgian astronomer, who relayed it in German to the senior Jugoslav, who passed it on to his companions in Serbo-Croat. This was no doubt why, at one stage, we showed pictures of mountain oxen chewing the cud rather than the eclipsed Sun!
I doubt whether next week’s eclipse will produce any stories as interesting or bizarre as those.
But you never know.
On the morning of 11 August 1999, I bumped into an old hippy mate of mine from the Carpenters days – a casualty of heavy alcohol and drug abuse during his younger days – walking his dog Poppy along the line. Later that same morning I saw him wandering through Aberdare – on his own.
My first thought was, ‘Oh, no! He’s sacrificed Poppy to bring back the warm yellow god in the sky!’
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