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Astronomy: An all-American eclipse

Nature volume 545, pages 409410 (25 May 2017) | Download Citation

Jay Pasachoff enjoys four books heralding this summer's US total solar eclipse.

American Eclipse: A Nation's Epic Race to Catch the Shadow of the Moon and Win the Glory of the World

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Liveright: 2017. 9781631490163

The progress of an eclipse seen from Australia in 2012. Image: Stocktrek Images/National Geographic Creative

On 21 August 2017, the United States will experience its first all-American total solar eclipse. The path of totality's full shadow — some 100 kilometres wide — will for the first time make landfall only in the United States, passing over the homes of 12 million people in 14 states, from Oregon to the Carolinas. Heliophysicists and umbraphiles from around the world are preparing for it, along with Department of Transportation officials. The former are still pondering the results of the 1999 eclipse, whose path crossed Europe from Cornwall to Romania and beyond, and of total eclipses since. The latter are doing their best to ensure that millions of drivers get safely into and out of the path.

“A total solar eclipse is the most stupendous sight in nature.”

The fuss is understandable. A total solar eclipse is the most stupendous sight in nature: the abruptly darkening sky; Baily's beads, glints of sunlight shining through lunar valleys; the dazzling diamond-ring effect; the spiky, pearly solar corona. Then, a couple of minutes later, the whole show in reverse. Equally compelling is the knowledge that you are witnessing a syzygy, an alignment of Earth, Moon and Sun that darkens the sky by an additional factor of 10,000 in the last minute alone. Now, four books all anticipate the coming celestial event in different ways.

In American Eclipse, journalist David Baron harks back to the total eclipse visible in the United States in July 1878. (I read this book in draft and provided a blurb.) A group of eminent scientists, including astronomer Henry Draper and his wife, Anna (see S. Nelson Nature 539, 491–492; 2016), travelled to Rawlins, Wyoming, to witness it. But, as Baron relates, 31-year-old whizz-kid inventor Thomas Edison gained the lion's share of publicity, even though he was just tagging along. Edison brought one of his devices, a tasimeter, to measure minute shifts in heat from the Sun's corona during the eclipse. He was unprepared for the strength of the signal, however, and his instrument's needle pinned at its maximum reading. It wasn't until around 1940 that physicists Walter Grotrian, Bengt Edlén and Hannes Alfvén found the solar corona to have a temperature of at least 1 million °C. Had the tasimeter worked, the scattering of sunlight that we see as the inner corona would have misleadingly given Edison the Sun's surface temperature, 6,000 °C.

Baron's stories are good ones, well told. The pioneering US astronomer Maria Mitchell — the first professor hired at Vassar College in Poughkeepsie, New York — took a group of alumnae, although they weren't offered free rail travel like their male counterparts. Astronomer and inventor Samuel Pierpont Langley, meteorologist Cleveland Abbe and solar spectroscopist-astronomer Charles Young also witnessed the eclipse. Nine years before, Young had co-discovered the green line in the spectrum of the corona that proved key in understanding coronal temperature; in the 1940s, it was found to come from iron gas so hot that many of its atoms have lost half their electrons.

In the Shadow of the Moon: The Science, Magic, and Mystery of Solar Eclipses

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Yale University Press: 2017. 9780300223194

The history of eclipses is global and long. Astronomer and science historian Anthony Aveni's In the Shadow of the Moon mines observations from five millennia. We learn about eclipses in ancient Babylonia, such as those recorded on a tablet fragment from 280 BC. Aveni analyses the story that the Greek philosopher Thales of Miletus predicted the eclipse of 28 May 585 BC, which supposedly halted a battle between the Lydians and Medes; he is sceptical of links between these ancient dates and actual eclipses.

He also delves into total eclipses seen in the United States, such as New York City's in 1925: people sat on roofs along the Hudson River to mark the shadow's lower edge on 96th Street, and the 'diamond-ring effect' was mentioned in the US media for the first time. Aveni concludes that neither rainbows, comets, meteors nor the aurora borealis surpass “the transient, exquisite beauty” of a total solar eclipse.

Eclipse: Journeys to the Dark Side of the Moon

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Oxford University Press: 2017. 9780198795490

Particle physicist Frank Close tells more-personal stories in Eclipse. In 1954, aged eight, Close viewed a partial solar eclipse; it inspired him to become a scientist. Although clouds all but foiled Close's attempt to see the totality from Cornwall in 1999, he managed to catch subsequent events from Zambia, Libya, Tahiti and, in 2013, a ship off the west coast of Africa. As he notes, “Like druids, who gather to greet equinoxes at Stonehenge, I had joined an international cult whose members worship the death and rebirth of the sun at moveable Meccas, about half a dozen times every decade”. Although he weaves in a modicum of history and science, this is essentially a travel book.

Mask of the Sun: The Science, History, and Forgotten Lore of Eclipses

By

Pegasus: 2017. 9781681773308

Like Close, astronomer John Dvorak hopscotches through eclipses in Mask of the Sun, but this is science history rather than anecdote. The quotes he interweaves reveal the extraordinary pull the events have had on the human imagination. The writer Virginia Woolf, for instance, who had witnessed the 1927 total solar eclipse in the north of England, wrote of it in her essay 'The sun and the fish' the following year: “Show me the eclipse, we say to the eye; let us see that strange spectacle again.”

It's a rich chronicle. Dvorak notes, for instance, how in 1684 Increase Mather, the president of Harvard College in Cambridge, Massachusetts, delayed the graduation ceremony by ten days so that faculty members and students could reach Martha's Vineyard off the state's south coast to see a total eclipse. (Mather, a Puritan minister, was less enlightened about the Salem witch trials less than a decade later, refusing to condemn them.) We see how astronomer Edmond Halley predicted the eclipse that crossed England in 1715, and gathered public observations to improve prediction of the 1724 event that traversed the country to Europe. And we are reminded of the part an eclipse played in Albert Einstein's rise to prominence. In his 1916 elaboration of his general theory of relativity, Einstein had predicted a deviation in the positions of stars near the Sun during an eclipse; three years later, English astronomer Arthur Eddington successfully measured it.

Along with other recent studies — such as astronomer Tyler Nordgren's fine Sun Moon Earth (Basic, 2016) and Mark Littmann and Fred Espenak's excellent and thorough Totality (Oxford, 2017) — these books should enrich the understanding of anyone interested in eclipses. They provide a worthy shelf-full for those gearing up for the big US event in August. (I will be viewing it — on my 34th total-solar-eclipse expedition — near the path's US start in Salem, Oregon.) And I hope they convince many others to view it live. If you're not in the zone of totality, just remember to wake up early enough to dodge the traffic jams.

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  1. Jay Pasachoff is Field Memorial Professor of Astronomy at Williams College, Williamstown, Massachusetts, and chair of the International Astronomical Union's Working Group on Solar Eclipses.

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Correspondence to Jay Pasachoff.

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