John Dvorak. Mask of the Sun: The Science, History and Forgotten Lore of Eclipses. Pegasus Books, 2017.

On 21 August 2017 a total solar eclipse will track across the United States, passing over twelves states, including five state capitals. As the day approaches, and 'eclipse fever' builds up, millions of Americans and visitors from around the world will make plans to see the awesome spectacle, hoping that the skies will be clear. Mask of the Sun has been published in good time for this great event and provides a thoroughly comprehensive guide to the science and history of eclipses, both solar and lunar.

John Dvorak, having trained as a lunar scientist, spent twenty years operating a large telescope at Mauna Kea, a dormant volcano whose peak is the highest point in the state of Hawaii. It is one of the best sites in the world for astronomical observation. Dvorak's hands-on experience is evident in his ability to explain the most complex scientific theories in an uncomplicated way to a general readership. He honed his writing skills with many articles for magazines such as Scientific American, and has already published two books on earthquakes and volcanoes.

There is only one sentence where an editor might have suggested a revision, where, after discussing the development of Stonehenge and its possible use as an astronomical observatory, he says: "At no time other than the present has Stonehenge ever looked the way it does today."

He might also like to ask his proof-reader how he missed a glaring error on page 69. Describing a British mission to Hudson Bay that departed from Bristol on 13 May 1631, on the same page he tells us that on the same voyage an eclipse of the Moon was recorded in the ship's log on 8 November 1831. I know those voyages could be lengthy, but 200 years?

At the beginning of the book is a map of the United States with symbols showing the path of totality, with exact timings of the start and duration of the eclipse on 21 August 2017 (already dubbed 'The Great Total Solar Eclipse') at various points across the continent. That feature alone will be of great value to anyone thinking of travelling to, or within, the USA for this rare opportunity. The next total eclipse over the USA will not be until 8 April 2024, and the one after that on 12 August 2045.

For many people it is a 'once-in-a-lifetime' experience to have a clear view of a total eclipse for a few minutes, and almost all of those will say it filled them with a sense of wonder that is never forgotten. I can certainly vouch for that myself, having witnessed the perfect total eclipse on the morning of 22 July 2009 from a boat on the river Ganges in the holy city of Varanasi, India. The headline of the English language newspaper in our hotel the next day read "God's Eye Shines over Varanasi". It was that kind of experience.

The fact that solar and lunar eclipses can be predicted with such pinpoint accuracy as to time and place is in itself a wonder. We may easily take it for granted in this computer age, but just a little consideration shows how extremely complex are the observations, measurements and variables in making those calculations. Dvorak guides the reader effortlessly from the earliest eclipse predictions of the Babylonians, and the methods they used, right up to the present day in which predictions are shown to be accurate to within one second. Along the way are many entertaining anecdotes and insights about the progress of human understanding through the ages.


In fact, rather than diving straight into ancient history, Dvorak starts his book with an entertaining Prologue about the observation of the total solar eclipse over the USA on 24 January 1925 from a giant airship the 'Los Angeles'. This vessel was the largest craft of its kind in the world at the time. It had been manufactured by the Zeppelin company in Germany and given to the United States after the First World War as part of the war reparations agreed in the Versailles Treaty. A cameraman stood on top of the airship cranking a manual movie camera to record the eclipse and suffered severe frostbite. This Prologue sets the tone of Dvorak's book.

Human emotions and sacrifices in search of knowledge are as important as the knowledge itself. He describes the effect of that 1925 eclipse on the city of New York, for example. The whole city came to a standstill for the eclipse. During totality there was at first silence, then spontaneous applause broke out. Some people stood and wept, others began to spin or wave their arms. People were leaning out of buildings, shouting and banging metal pans, or anything else that came to hand. It will be interesting to see what mass effects the forthcoming eclipse on 21 August 2017 will have.

That eclipse of 1925 was the first total solar eclipse to pass over a broad region of the world that was connected by telegraph links, so providing the first opportunity to measure the speed of the Moon's advancing shadow. Telegraphic operators were stationed at key points along the path of totality with an unobstructed view of the sun. At the moment when the last ray of sunshine was hidden by the moon, indicating the arrival of the shadow, that particular operator was to press a special key connected to a recording station. Bell Telephone engineers had devised a new mechanism that would record the arrival of each signal to within a tenth of a second. The result? The average speed of the moon's shadow was about 3,500 miles per hour, or nearly one mile per second. That explains why totality arrives so suddenly. Even if the moon's coverage of the sun is 99% there is still enough light to make everything look normal. But at totality there is a sudden unearthly darkness, a cooling effect and a sense of silence.

Birds in particular are confused by the onset of darkness in a total solar eclipse. Dvorak gives some amusing examples of various animals' reactions at such times and the most memorable of these concerns Thomas Edison. For the solar eclipse of 1878 he had invented a new type of scientific instrument to measure the temperature of the sun's corona. It was a delicate instrument so he sought a quiet sheltered place to set it up. On the day of the eclipse he found a vacant shed with a doorway that would give an unobstructed view of the coming phenomenon. Just as darkness descended and he began to take the first measurement a flock of chickens rushed into the shed, taking him totally by surprise and disrupting his experiment as they flapped all around him. He had unwittingly chosen a chicken coop, and the chickens had come home to roost!

Dvorak entertainingly tells all you need to know about eclipses. He explains how and why they were viewed as bad omens before the scientific age, and how kings and even popes took steps to protect themselves from an untimely death. In some cases they did die near to the time of an eclipse, adding to the mystique and fear. He gives examples of how foreknowledge of an eclipse might be used to impress superstitious native peoples, such as the case of Christopher Columbus in Jamaica in the year 1503. Using an almanac he was able to predict a lunar eclipse and, having called the local leaders to a meeting he persuaded them that God was angry with them for not providing enough food to him and his men. The rising of a blood-red Full Moon did the trick.

This is a book about human endeavour to understand the heavens above us, and the meaning of celestial events. To understand eclipses is to have knowledge about planetary motion, orbits, forces of gravity and cycles of time. The Babylonians were the first to record cycles of planetary and lunar alignments. Newton taught the world about gravity and the laws of motion. Einstein revolutionised the understanding of the space-time continuum and the effect of the sun's gravity on rays of light from distant stars. It was through studying eclipses that much of this knowledge was gleaned, often through extreme trial and error and much disappointment. Mask of the Sun tells the whole tale superbly. -- Kevin Murphy

For a curious social and moral panic that is building up about this eclipse, see http://www.wdrb.com/story/35850973/hopkinsville-on-high-alert-for-sex-trafficking-around-next-months-solar-eclipse

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