By Joe Rao
Eclipse Bulletin: Total Solar Eclipse of 2017 August 21 by Fred Espenak and Jay Anderson
Astropixels Publishing, 2015. ISBN 978-1-941983-05-8 156 pages
Black and White or Color Editions can be ordered here at: http://astropixels.com/pubs/TSE2017.html
There can be no denying the value of this book. Fred Espenak – better known to eclipse chasers around the globe as “Mr. Eclipse” – is the established authority on eclipse calculations; before he retired from NASA/Goddard, from 1993 to 2008 he published 13 similar eclipse bulletins (with coauthor Jay Anderson). This latest bulletin was published sans NASA funding and is by far the biggest and most extensive eclipse circular that he has ever produced. Amateur astronomers even just vaguely interested in the subject of eclipses should have come across his work by now. If not, now is the time to start.
The title accurately describes the aims and objectives. Anybody who intends to witness firsthand the long-awaited 2017 “All American Eclipse” may have already given some thoughts as to where they intend to be on eclipse day, but I would regard this book as essential reading at any time. If, for example, on eclipse day I’m driving along an unfamiliar road within the path of totality, I would want this book within arm’s reach.
As a broadcast meteorologist and eclipse chaser with ten totalities under my belt, I always consider the first problem (apart from money), as to how to deal with the weather prospects. Few have the necessary expertise to make a balanced judgement, and that is where this book is particularly valuable. Jay Anderson, formerly with Environment Canada (Canada’s national meteorological service) has written extensively on the climatology of places along eclipse tracks for nearly four decades and is eminently suited to be your guide; as such, much space is devoted to the merits of each practical region along the totality path.
Each region is treated to a detailed critique, finishing with some specific recommendations. Mr. Anderson, however, goes further than that, to list statistics on the climate and then summarize them in the form of diagrams, maps, graphs and tables. I especially found the tables containing cloud-cover statistics most valuable.
Over the years, I’ve used a simple formula which provides a representative percentage value for the chance of seeing the Sun in a blue sky. For this I use the average percentage of total cloudiness, as well as the percentages of a clear and partly cloudy sky. Usually, I’ve had to dredge these statistics up on my own, but Mr. Anderson’s tables has saved me the work. Of the 38 locations within the totality path, my own subjective percentages ranged from a high of 85.1 for Ontario, Oregon to a low of 43.8 for Charleston, South Carolina.
Of course one must also remember that any statistical climate analysis is not absolute, as is evidenced by the oft-quoted axiom by the late Robert Heinlein: “Climate is what you expect; weather is what you get!” (As so many who headed to the Big Island of Hawaii in 1991 painfully learned!)
I particularly enjoyed the section dealing with the travelogue along the umbral path undertaken by Mr. Anderson and fellow Canadian, Stan Runge. I got a chuckle out of the anecdote concerning the owner of the farm closest to the point of greatest eclipse in Kentucky. According to the unnamed owner, he already is getting dozens of people who visit his property each week “looking for the eclipse track.” When Mr. Anderson told him that he’ll have “quite a crowd” on eclipse day, the owner replied: “Maybe I’ll let my grandkids set up a lemonade stand. Except the bureaucrats will want them to get a license.”
Here is something which should be looked upon not as a criticism but a suggestion:
The possibility of a tropical cyclone when speaking of weather prospects for South Carolina and its adjacent coastal waters was not considered. While the odds for a full-blown tropical storm or hurricane situated near the South Carolina coast exactly on August 21 is rather small, the prospects for any sort of tropical system does increase rapidly after August 1 and "E-day" comes only 20 days before the traditional peak of hurricane season in the Atlantic basin. Recent systems that have passed relatively close to South Carolina in late August/early September include "Irene" (8/27/11), "Hanna" (9/6/2008), "Ernesto" (8/31/2006), and "Gaston" (8/29/2004).
Of course, nobody in Charleston will ever forget Hurricane “Hugo" (a Category 3) which scored a direct hit there, but in late September (9/22/89). And even a tropical system that makes landfall hundreds of miles away (say, along the Gulf Coast), might adversely impact the totality zone by spreading clouds and remnant rains to the north and east into the eclipse path. Old-timers in southern New England, for instance, will recall the total eclipse of October 2, 1959 which was unfortunately ruined by the remnants of Hurricane “Gracie.”
The remainder of the book is crammed with tons of information on the 2017 eclipse and how to predict the shadow path, how the saros (#145) has changed over time and how it compares with other cycles, and much, much more. About three dozen maps depicting the totality path as well as the visibility zone of the entire eclipse are included. I love the stereographic projection map on page 13. Now if only concentric contours for the semi duration of the partial phases – a personal preference – could also be added. The United States Naval Observatory (USNO) has always used stereographic projection for their eclipse maps, but discontinued the practice of depicting semi durations in 1983.
Local circumstances for more than a thousand cities across North America, as well as northern South America, northwest Africa and Western Europe are provided with times for each phase of the eclipse along with the eclipse magnitude, obscuration value and Sun’s altitude. For any specific location that has not been listed, a good compromise can be obtained by means of simple interpolation. For those places inside the eclipse track, the duration of totality is provided as well as the umbral depth.
It is good that on page 32, Mr. Espenak explains the reason why the Bulletin departs from the International Astronomical Union (IAU) convention, adopted in August 1982, of using a slightly larger value for the mean lunar radius, noting that to employ it “. . . guarantees that some annular or annular-total eclipses will be misidentified as total” (A good case in point, would be the recent eclipse of 2013 Nov. 3). As such, the 2017 Bulletin adopts a smaller value (k = 0.272281) which produces a shorter central duration and a narrower path of totality. This explanation is important for those who decide to utilize the eclipse predictions by the USNO, which bases its computations on the IAU’s larger value.
The USNO has recently posted a web page which allows anyone to generate local circumstances for the 2017 eclipse (athttp://aa.usno.navy.mil/data/docs/Eclipse2017.php) and indeed, the duration of totality ends up slightly longer and the path width is somewhat wider. As an example, at the point of greatest eclipse duration, the Bulletin gives a value of 2m 40.3s compared to 2m 42.5s for the USNO, a difference of 2.2 seconds.
There is a section providing valuable tips on eclipse photography and perhaps most important of all for eclipse neophytes, a section concerning eye safety, written by Dr. B. Ralph Chou, Professor Emeritus, School of Optometry and Vision Science at the University of Waterloo, in Ontario, Canada, and Past President of the Toronto Centre of the Royal Astronomical Society of Canada. It was Dr. Chou’s pioneering research in the effects of solar radiation on the eye that confirmed that aluminized Mylar was safe and effective for use in observing solar eclipses and which helped lead to its widespread adoption by the astronomical community, and therefore, by the public at large. Notes Mr. Espenak: “Dr. Chou’s contribution should help dispel much of the fear and misinformation about safe eclipse viewing.”
The 2017 Bulletin finishes with a thorough bibliography as well as a chapter titled Eclipse Marketplace, which provides a listing of products for safely viewing the Sun and solar eclipses as well as companies who will be running eclipse tours for the March 2016 eclipse as well as the August 2017 event.
In any book of this detailed statistical nature, it is to be expected that there will be typographical errors. While there may be some who delight in finding such things, that effort should not be allowed to detract from the true value of this book.
I myself ran across a couple of very minor typos, but as Mr. Espenak recently commented on the Solar Eclipse Mailing List (SEML): “One of the great things about the print-on-demand process I'm using for the ‘2017 Eclipse Bulletin’ is that I can make corrections and updates to the manuscript whenever necessary.” So the typos I found in my copy are likely to be gone for anyone who now purchases their own copy.
In fact, to augment the plethora of data already provided, Mr. Espenak has just created a web page (http://www.eclipsewise.com/solar/SEnews/TSE2017/extra.html) which contains links to additional tables, information and yes . . . errata.
Lastly, I was happy that in the Acknowledgements, Mr. Espenak gave a “shout out” to the great Belgian celestial mechanic, Jean Meeus, who stimulated many of us into the world of eclipse calculations with his 1966 classic Canon of Solar Eclipses. Indeed, without Meeus’ incentive, the 2017 Eclipse Bulletin might not exist.
What more can I say? If you plan to “bask in the shadow of the Moon” in 2017, this book is for you!
News 12 Westchester/Hudson Valley