On Monday April 8, 2024, a total solar eclipse, which the media is calling the “Great American Eclipse,” will be crossing the central eastern U.S. from Texas through New Hampshire. Although on average two solar eclipses (total or annular) occur somewhere on Earth each year, the location of path of totality varies on a periodic cycle and the orbital tilt of the moon, which means observing an eclipse in the same place on Earth can take decades or centuries to reoccur and thus, for many, witnessing an eclipse is a once in a lifetime event. Some of you may have witnessed the total solar eclipse of August 21, 2017, which was seen by an estimated over 10 million Americans (including this author!), or the annular solar eclipse we experienced just last year on October 14, 2023. However, the upcoming total solar eclipse in April is the last of this saros cycle, which means that this is your last chance to see a total solar eclipse in the continental United States until August 2044!

Timeline for the partial solar eclipse as viewed from the Niels Bohr Library in College Park, MD 20740 from NASA’s Eclipse Explorer.

Although College Park, MD where the Niels Bohr Library & Archives is located will not fall into the path of totality, we are looking forward to observing the partial (87%) eclipse here. You can see how close you are to the path of totality and tips from NASA for viewing the eclipse safely here and for tips on how to take photos of both partial and total eclipses safely check out this guide from the AAS, which are both linked in our new eclipse resource page.

Be sure to also check out the rest of our new LibGuide: Solar Eclipse Resources at NBLA for other eclipse related resources from the Niels Bohr Library & Archives, including this interview from our Oral History Collection with life-long eclipse chaser and Williams College Astronomy Professor Jay Pasachoff, who witnessed 74 solar eclipses in his lifetime (likely more than anyone else in human history!) between 1959 and his death in 2022.

Introduction:

Total solar eclipses have been a subject of human and scientific fascination for millennia. However, it wasn’t until the 19th century and the advent of photography and spectroscopy, which significantly changed the nature and prospect of solar observations, that eclipses became a major scientific focus. Total solar eclipses provide a unique opportunity to study the sun’s coronasphere, a part of the sun’s atmosphere only observable during eclipses. The study of eclipses has also led to a number important scientific discoveries including the element Helium (named after the Greek sun god “Helios”) and the confirmation and popularization of Einstein’s Theory of General Relativity through Arthur Eddington’s observation of gravitational lensing during a total solar eclipse in 1919.

Expeditions to observe eclipses, often organized by observatories, universities or scientific societies, became quite common in the 19th century, with parties of astronomers being sent to locales around the world with bulky telescopic equipment to observe and record data from the event. The Victorian Era also dawned the age of “eclipse tourism” with amateur astronomers and wealthy society also taking part in expeditions, traveling in relative luxury to remote locales in the British Empire to witness the spectacle (for more on this phenomenon see Alex Soojung-Kim Pang’s 1993 article in Isis  “The Social Event of the Season: Solar Eclipse Expeditions and Victorian Culture.” )

Whether you are staying put or mounting your own expedition to see the April 8th, 2024 total solar eclipse, for this Photos of the Month, we are going to explore what went into the Solar Eclipse Expeditions of the late 19th and early 20th century using the Emilio Segré Visual Archives!  

How to mount a Solar Eclipse Expedition -- Victorian Style!

Part 1: Planning

Timeline: Years to months in advance

Organizing a solar eclipse expedition is no mean feat. Details would be meticulously planned months to years in advance including carefully identifying the path of totality, planning an observation program, securing funding, diplomatic passports, and transportation for large, fragile equipment and lodging for big groups of people. Getting everything in place in time for an event lasting only minutes was (and still is) a massive scientific and logistical undertaking. Despite this, the reward was worth it, not only for the scientific data but also for the human and social experience of viewing one of nature’s most amazing spectacles (although weather always risked disappointment). Astronomers would travel to get the chance to observe solar phenomena such as the coronasphere and families, patrons, and friends would tag along to make it a vacation. Below is a photograph of the 1923 Eclipse Expedition to Santa Catalina Island organized by Yerkes Observatory of Chicago, which included several notable astronomers (including Annie Jump Cannon and Donald Menzel) and their families.

On the Yerkes Observatory expedition to Santa Catalina Island, California (Camp Wrigley) to record the total solar eclipse of September 10, 1923. Yerkes Observatory E9 (Catalog ID) Credit Line: Photograph by B. W. Harris, Yerkes Observatory, University of Chicago, courtesy of AIP Emilio Segrè Visual Archives, Yerkes Observatory Collection. 

But what actually went into planning an eclipse expedition?

Predicting the Eclipse and the Path of Totality:

First scientists needed to calculate the path of totality. To get any meaningful data on an eclipse, astronomers need to be in the path of totality, or the area darkened by the moon’s shadow on earth, to observe the sun’s corona. Predicting this path can be done through an understanding of the orbital dynamics of the sun, earth and moon to determine when and where an eclipse will occur decades and centuries in advance. This would be narrowed down working with maps and tables from national authorities, to identify where in the world the eclipse would be visible, down to the latitude, longitude, and time, accurate to within a few hundred yards, which could be the matter of success or failure for an expedition. 

Smithsonian Astronomical Observatory astronomer Brian Marsden recollected in his 2005 Oral History Interview that his interest in astronomy stemmed from predicting the path of solar eclipses as a child, one of which he got the chance to observe nearly 50 years later:

You have to wait a very long time. Some things I knew we’d have to wait a long time. When I was playing around with that perpetual calendar in elementary school, showing the students, one date I knew was August the 11th, 1999, which was quite a long time in the future then, and I knew that was the next eclipse visible from England. So I did make a point going back to England around that time to experience it. I didn’t see it because it was cloudy, but we certainly experienced it because we were on a cliff in Devon, and you could see the shadow very nicely.

… It was a west-facing cliff. It would be nicer to see the eclipse, but in the meantime, I had seen two other total eclipses of the sun, so I didn’t need to see this one. But I wanted to experience it, going back to those much earlier dates when I’d tried my own prediction for it. There were people at the time saying, “Well, the eclipse may not be visible in England. It may be off the coast.” I remember doing a beautiful map for my own calculations, and I wish I could find it….My prediction was in the early 1950s. At that time there was some uncertainty due to all the irregular rotation of the Earth, one couldn’t predict forward the ?T [Terrestrial Time] too well. People were very uncertain about that. And there was a rumor going around that it might not be visible unless you were right on the coast. I mean, you’d only see it if the tide was out. [Laughs]...I remember people joking about — I think it was a joke. I did a calculation, and I wish I could find it; it obviously was destroyed long ago. I would always have liked to have compared it to what was calculated much later when we knew what the ?T [Universal Time] was. But my recollection is that it was about right, because quite a lot of southwestern England was in that total path.

Left to right: George Hale, Arthur Noyes and Harry Goodwin.; Solar Eclipse, Wadesboro, North Carolina; May 28, 1900. Hale George C6 (Catalog ID) Credit Line: Photograph taken by Jean Wilson, Smithsonian Institution, courtesy AIP Emilio Segrè Visual Archives. 

Choosing an Observation Spot:

Next, an observation spot would be chosen for an expedition within the path of totality, taking several factors into account. Seasonal weather maps and forecasts would be meticulously consulted with anticipation, knowing that months of planning could be ruined by just one moment of bad weather. A good observation point needed to be close to railroad stations or ports (for transporting sensitive and increasingly large telescopic equipment and accommodating party travelers), but far enough away from civilization to have low haze from dust and smog. There needed to be clean water (for developing photographs) and relatively smooth terrain (for leveling equipment) and access to communication lines for reporting data.

For example, in the May 28th, 1900 Eclipse in the southern United States, a 3-year study was commissioned from the US Weather Bureau in preparation for the eclipse, which was then used to determine the best spots for observing. Based on the weather results and proximity to rail and communication lines, several American Astronomers determined that Wadesboro, North Carolina would be the best spot to observe totality, resulting in sizable teams from the Smithsonian Institution (led by Samuel P. Langley), Princeton University (led by Charles A. Young), Yerkes Observatory (led by George Hale (see photo above)), and the British Astronomical Association along with many others. (For more on the 1900 Solar Eclipse Expeditions in Wadesboro see the May 2023 This Month in Astronomy History from the Historical Astronomy Division of the American Astronomical Society).

International Considerations:

If traveling internationally, political tensions and diplomatic logistics also had to be taken into account. In preparation for the 1965 solar eclipse in the South Pacific, Frank Beaston recalls undertaking a massive diplomatic effort to convince the Cook Islands to allow international scientists to visit the country to observe the eclipse, which they were reluctant to do for fear of an international incident; a previous expedition to the region had resulted in English and New Zealand scientists coming to blows, which gave international astronomers a bad reputation. Eventually,

...the expedition was a great success. Unfortunately a huge black cloud came over at the wrong moment. Radio people got good results, the optical people didn’t. But it was a wonderful example of international cooperation in astronomy. There was no hitch whatsoever from the word go.

Below is a photo of an eclipse team with former AIP Center for History of Physics director Spencer R. Weart, observing this same 1965 Total Solar Eclipse in the South Pacific, although his party was based on an uninhabited island in French Polynesia.

Group at Bellingshausen (Motu One) in the South Pacific for the 1965 Total Solar Eclipse. Weart Spencer D7 (Catalog ID) Credit Line: AIP Emilio Segrè Visual Archives, Jefferies Collection 

Observation Program and Equipment:

After a spot was chosen, an observation program would be developed determining what methods and equipment would be needed or was feasible given risks transporting equipment long distances and for payout. Funding also needed to be secured to make equipment and fund transport and travel arrangements. In the late 19th and early 20th century, observations of the sun’s coronasphere were highly sought after since they were only observable during an eclipse. Later expeditions different features were studied: radio observers were fine cloud or shine, while optical observers were dependent on clear weather. 

These observation plans would vary according to the skills, resources, and abilities of the astronomers on the expedition. In January 1900, in advance of his Eclipse Expedition to Wadesboro, NC, George Hale published in the Astrophysical Journal a list of instructions for suggested observation methods at increasing levels of complexity for amateurs and newcomers in solar work with limited equipment or practical experience to consider. This observation program included:

1. Naked-eye drawings of the corona
2. Drawings at the telescope
3. Color of the corona and prominences
4. Small-scale photographs of the corona
5. Photographs of the corona during the partial phase
6. Photographic search for possible intra-Mercurial planets
7. Large-scale photographs of the corona and prominences
8. Distribution of “coronium”
9. Position of the green coronal line
10. Photographs of the spectrum of the chromosphere
11. Photographs of the spectrum of the corona
12. Heat radiation of the corona

From Hale, George “Solar Eclipse Problems” ApJ vol. 11, p. 47 January 1900 DOI: 10.1086/140667

Part 2: Preparing the Observation Site

Timeline: Weeks before the Eclipse

Charles Abbot with the bolometric apparatus during the Astrophysical Observatory Solar Eclipse Expedition, 1900. Abbot Charles F2 (Catalog ID) Credit Line: Smithsonian Institution, courtesy AIP Emilio Segrè Visual Archives

Preparing an observation site for the eclipse was a challenge all on its own. Expeditions with equipment were sent down weeks in advance to prepare the camps for observations, building tents and telescopes so that on the day all the observations could go smoothly. In May 1900, the weeks leading up to the eclipse were abuzz with activity in Wadesboro, North Carolina.

The Smithsonian Institution, led by Samuel P. Langley, sent down several trains full of equipment from DC to Wadesboro in advance of the eclipse. In the photo above, you can see astrophysicist Charles Abbott inspecting and demonstrating a bolometric apparatus among crates from the train.

The Yerkes Observatory from Chicago built a photographic house and a photoheliograph for the occasion, with workers out over a week in advance of the eclipse to get it ready. In the photo below, men are building a long tubular chamber that will connect a mirror (on the left) to a dark photography room on the right, which will direct the sun’s image onto photoheliographic plates, which will be developed in the onsite dark room. 

 It was only through incessant work from morning till night for 2 weeks…for the four minutes of darkness, so precious to science" (Herbert Hall Turner, 1886 as quoted in Empire and the Sun, p. 66)

Four unidentified men surround the tube of a photoheliograph and photographic house at the Wadesboro, North Carolina solar eclipse camp, May 19, 1900. Yerkes Observatory H19 (Catalog ID) Credit Line: Yerkes Observatory, University of Chicago, courtesy of AIP Emilio Segrè Visual Archives, Yerkes Observatory Collection. 

For more recent eclipses, equipment for observing has evolved, allowing for new ways of observing eclipses through radio, infrared, and x-ray, but also for some new complications in setting up equipment on site! 

In the first of the photos below, we see the preparation of dewars (cryogenic storage chambers) which will be used to cool down far-infrared detectors using liquid helium, so they can be used to make observations of a solar eclipse in Guam. After that is a photo of a group of astronomers setting up a shade for sensitive equipment from the joint Solar Eclipse Expedition of the High Altitude Observatory, Sacramento Peak Observatory and the National Bureau of Standards to the February 1962 solar eclipse in Lae, New Guinea.

Tom Roellig (NASA Ames) and Stanford graduate student Greg Kopp, 1988, emptying liquid nitrogen from the detector dewars prior to cooling them with liquid helium. They would use the detectors to make far-infrared observations of a solar eclipse. The expedition was based at Anderson Air Force Base on Guam, where this picture was taken. Roellig Thomas C1 (Catalog ID). Credit Line: NASA, courtesy of AIP Emilio Segrè Visual Archives, Erickson Collection.

Bob Lee (cap), John Jefferies (hat), Dick Dunn (bareheaded) at the Lae New Guinea total solar eclipse. February 1962. Jefferies John F1 (Catalog ID) Credit Line: AIP Emilio Segrè Visual Archives, Jefferies Collection

Part 3: Last minute inspections

Timeline: Day of the eclipse

The day of the eclipse has finally arrived and the final preparations begin. Eclipse parties arrive to inspect the equipment set up prior to their arrival and telescopes and measuring instruments are carefully calibrated, with communication lines set up to local chronometers and measuring stations.

In the photographs below, we see American astronomer Charles August Young (1834-1908), a noted professor of astronomy at Princeton University who led several solar eclipse expeditions, inspecting equipment on the day of an eclipse. Young was an early pioneer in solar spectroscopy and studied multiple eclipses in his lifetime, taking him as far as Spain (1870) and Russia (1887). These two photographs show Young on an expedition during his student Henry Norris Russell’s time at Princeton, circa 1897 or 1898. In the first photo, Young is standing in front of a wide-field astrograph loaded with photographic plates and in the second, a multi-lens spectrograph.

Charles Young (foreground), stands with a wide-field astrograph during a solar eclipse expedition circa 1897-1898. Young Charles F4 (Catalog ID) Credit Line: AIP Emilio Segrè Visual Archives, Margaret Russell Edmondson Collection

Charles Young (right)  and an unidentified man  with spectroscopic equipment, circa 1897-1898 Young Charles F1 (Catalog ID) Credit Line: AIP Emilio Segrè Visual Archives, Margaret Russell Edmondson Collection.

Final moments waiting for the eclipse to start:

The last few minutes before the eclipse starts, after all equipment has been calibrated, is the calm before the storm.

Prior to the total solar eclipse of May 28, 1900: S. A. Mitchell, late Prof. of Astronomy, Univ. of Va.; Schneider, a skillful technician from Johns Hopkins University physics laboratory; S. J. Brown, then astronomical director of U.S. Naval Observatory; Henry Crew, Head, Dept. of Physics, Northwestern University at Griffin, Georgia, Crew Henry H1 (Catalog ID) AIP Emilio Segrè Visual Archives, Henry Crew Collection 

Part 4: The Eclipse Begins

Observations begin being recorded:

Once the first sliver of the moon passes into the sun’s path and the eclipse begins, so do observations. Chronometers are synced with local authorities and observations are sent live between sites and home observatories through local telegraph and radio offices.

In the photo below, we see Joseph Horton timing the 1925 solar eclipse. During the solar eclipse, a number of observation posts in the United States and in the North Atlantic were connected by telephone lines and radio to the Bell Laboratory in New York. Signals marking the transit of the moon's shadow were recorded on a moving tape together with time marks from the standard frequency tuning fork. The times of these transits were recorded with an accuracy of better than 0.01 second.
 

Joseph Horton times a 1925 eclipse. Horton Joseph F4 (Catalog ID) Credit Line: Bell Laboratories / Alcatel-Lucent USA Inc., courtesy AIP Emilio Segrè Visual Archives, Physics Today Collection

Part 5: The Moment of Totality!

After hours of slowly watching the moon pass in front of the sun, the sky suddenly darkens and the moment that is the source of months of anticipation has arrived!

If the expedition is lucky, the weather is fair, and the party is able to witness the spectacular solar corona and other atmospheric effects. Below is an image taken of the solar corona during the 1922 total solar eclipse by Lick Observatory.

Photo from the 1922 eclipse taken at Lick Observatory. The astronomer Arthur Eddington said it was the greatest moment of his life when he measured the image of a star and found that the sun's gravity warped the space through which the light had traveled. This photo taken at Lick Observatory is from the 1922 eclipse where the effect was reconfirmed. (The stars are not visible in this reproduction. What you see are circles drawn around them.) Lick Observatory H1 (Catalog ID). Credit Line: Lick Observatory Archives, courtesy of AIP Emilio Segrè Visual Archives. 

To see more images of the solar corona and give an idea of the type of data collected at these eclipse expeditions, check out this eclipse archive from the High Altitude Observatory which has photographic data of eclipses going back to 1869! 

Not every eclipse expedition is a success though. Cloud cover, foul weather, technical problems, equipment malfunctions, all can ruin the precious few minutes of data taking during totality. It is a risk every expedition must take, that for all the work and resources of planning, there is an equal chance of failure as there is for success. Even under cloud cover however, there is some consolation, since even without the ability to take good data or see the corona, the eerie effect of the sudden darkness is still impressive. To get a sense of what witnessing such a “failed” solar eclipse is like, we have in our collections a silent home movie from National Bureau of Standards spectroscopist William F. Meggers from his solar eclipse expedition to Lund, Sweden on June 30, 1954.

Megger’s commentary of this footage (edited for clarity) paints a vivid picture of the anticipation, disappointment, and silver linings of an eclipse party foiled by clouds:

Thumbnail Image: National Bureau of standards spectroscopists Carl Kiess, Charlotte Sitterly, and William F. Meggers (wearing an eclipse necktie) pose after the solar eclipse, June 30, 1954.

30 June. Eclipse expedition, Lund to Lyckas (86 people in the party). The eclipse party leaves the train at Jankoping (K.W. Meissner of Purdue wears a beret) and then boards buses for Lyckas (0:21). After the bus ride, the party then walks two kilometers over hills to the center of the eclipse (Julian Mack of Madison visible) (0:27). There is a long procession to eclipse (deBruin and Kiess visible at 0:36). A sign in Swedish reads “To the press - photography with flash light during eclipse absolutely forbidden" (0:38). Now at 1 PM, standing on the exact center of the eclipse path they wait for the total eclipse (0:42). It gradually gets darker and then blackness comes suddenly and lasts 137 seconds (dense clouds obscures all) (0:55). Ten minutes after totality William F. Meggers poses with the NBS spectroscopists Carl Kiess and Charlotte Moore Sitterly, displaying his eclipse necktie (1:09). A professor lectures to a disappointed crowd (1:11) but then some wild roses cheer them up (1:26). The party then tramps down the hill and passes foiled eclipse observers from above (1:32). They return to buses and to grass-covered "Gyllene Uttern"  (Golden Otter) Restaurant for supper (free) and presents. (1:51). At last, bright sun breaks through clouds, albeit four hours after the eclipse! (2:12)

We hope that your April 8, 2024 viewing of the eclipse will be a success! We would love to hear your stories of the 2024 eclipse (or past eclipse expeditions you have been on)! Share them in the comments or on our social media pages! And even if clouds or rain damper the occasion, you can always watch the NSF livestream of the eclipse from your own home here: https://new.nsf.gov/events/solar-eclipse-2024

Bibliography and Further Reading:

Bartusiak, Marcia. Archives of the Universe : a treasury of astronomy's historic works of discovery edited and with introductions by Marcia Bartusiak. Pantheon Books: New York, 2004. KF ARC

English, Thomas. ““The Best Place on the Face of the Earth:” Wadesboro and the 1900 Total Solar Eclipse” AAS: This Month in Astronomical History, AAS Historical Astronomy Division, May 2023 https://aas.org/posts/news/2023/05/month-astronomical-history-may-2023

Hale, George E. “Solar Eclipse Problems.” Astrophysical Journal, vol. 11, January 1900, pg. 47 DOI: 10.1086/140667

Interview of Frank Bateson by Stephen Dick on 1985 May 16, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA www.aip.org/history-programs/niels-bohr-library/oral-histories/4497

Pang, Alex Soojung-Kim. “The Social Event of the Season: Solar Eclipse Expeditions and Victorian Culture.” Isis, vol. 84, no. 2, 1993, pp. 252–77. JSTOR, http://www.jstor.org/stable/236234. Accessed 12 Feb. 2024.

Pang, Alex Soojung-Kim. Empire and the sun : Victorian solar eclipse expeditions Stanford University Press, 2002. H8:19 PAN

William F. Meggers home movies [motion picture], 1927-1959. AV 2017-2578; AR-614; AV V-1998 (15-24). American Institute of Physics. Niels Bohr Library & Archives. One Physics Ellipse, College Park, MD 20740, USA