A honey sun

05 Aug


Total eclipse of the sun showing Baily’s Beads, solar flares and the sun’s corona (1860) by Warren de la Rue. [1]

This is an image I have been admiring for months now.  I admire it because in just the smallest amount of detail and delicious colour – a sphere of dark amber, sparkling at the edges, in a background field of honey gold – the photograph is serenely ablaze with a vast wealth of knowledge that spans many disciplines: science, invention, travel, astronomy, art, adventure, history, chemistry and photography. And to it we can now add printing, computer science, imaging, and social media. It is the very definition of succinct.

And this is its story.

Warren de la Rue and Father Secchi

Until the arrival of early afternoon, Wednesday of July 18th in 1860 was like any other weekday in Spain. As was the custom, the hot sun had driven Spaniards into their cool homes for siestas. But for Warren de la Rue, the midday sun was a ticking clock, counting down to the 2:36 pm endpoint to which his previous several days had been in aid of, when the Earth’s moon would slip across the face of the sun and obscure it in a rare total eclipse. He had traveled many miles from London to Rivabellosa near Miranda de Ebro in the North of Spain, complete with assistants and 2 tonnes of equipment: his newly designed photoheliograph camera, photographic lab with solutions and glass plates, drapes and lamps, [2] (and perhaps his comestibles[3]).

At the same time, Father Angelo Secchi, an Italian astronomer and Jesuit, was arranging his own telescope and camera to photograph the eclipse, 500 kilometers away in Desierto de las Palmas, a small town 2500 feet above sea level recommended by the the Spanish Anuario as a choice location for viewing. (Perhaps the prospect was further facilitated by the presence of a convent in the area offering accomodation and the mere 2 mile trek from the high road.) [2 p34]

“Above all, Father Secchi believed A caeli conspectu ad Deum via brevis ( Contemplation of the heavens is a short way to God. )” [6]

Secchi and de la Rue were in place to use the eclipse of 1860 to photographically capture the halo reported by observers of previous solar eclipses, and to solve a mystery: the nature and source of ‘Baily’s beads.’

Baily’s beads

“…a row of lucid points, like a string of bright beads.”

Baily’s beads were first noted by their namesake, British astronomer Francis Baily, during the 1836 annular solar eclipse. Baily was amazed to see tiny beads of light in the glowing outline of the sun behind the moon. These beads of light became known as Baily’s beads, and were the subject of intense speculation for the next quarter century. Although there were many observers of the next eclipse, reports were inconclusive, and in 1860 the perfect confluence of a total solar eclipse plus the photographic expertise to record what might be revealed allowed the true nature of Baily’s beads to be known.

The expeditions were illuminating.  Warren de la Rue captured stunning images with his heliograph camera including one of the total eclipse. The images captured proof of the beads Baily described, and together with Father Secchi’s images, confirmed Baily’s conjecture that the beads of light were caused by the sun’s light streaming through the irregularities of the moon’s edges, varied from complete roundness by mountains, valleys and craters. But the photographs didn’t show just the beads.They also showed the solar corona, a halo of sunlight around the darker moon that Baily had eloquenly described:

“…I was astounded by a tremendous burst of applause from the streets below, and at the same moment was electrified at the sight of one of the most brilliant and splendid phenomena that can well be imagined. For, at that instant the dark body of the moon was suddenly surrounded with a corona, or kind of bright glory, similar in shape and relative magnitude to that which painters draw round the heads of saints.” [4]

Solar flares burst into prominence

Secchi and de la Rue’s photographs showed us something else that had never before been recognised: strings and splashes of light matter streaming out from the sun’s surface. Through these photographs, only 156 short years ago, we first learned the sun sent out solar flares.  An important consequence of Secchi and de la Rue taking photographs so far apart from one another was that they could prove that the corona was a solar phenomenon and not a lunar one, because the features of the corona were identical despite the 500 kilometer separation of the two astronomers which would have meant differences in the images from the differing angles were the phenomenon to be lunar.

And now to the honey gold: lingering sulfides and age

You may know that the collodion photographs of the mid 19th century were achieved through the use of photo-sensitive qualities of silver, just as black & white film was in the 20th century. So how did this photograph, which must have been black with white flares when taken, become the golden-hued beauty it is today?

At first, I had thought someone had performed some global colour changes on photograph prior to printing it. But in recent months I have learned more about the chemistry of 19th century photography, and discovered it is more likely that the golden colour of the image is the result of a happy error.


B&W version of total solar eclipse, (1860) Rivabellosa, Spain.  Photo: Warren de la Rue [6]

The culprit is probably excess sulphur remaining on the print after insufficient washing of the print.  Fixing baths for collodion images were made with hyposulphite.  If any of the hyposulfite remains on the print after washing, the sulphur can fade black and white images to shades of gold and brown. In many cases this would be a pity; in this case it has created a thing of beauty. [5]

Within this photograph, below its surface, powerful forces are at work: the attraction of electrons from one molecule within an emulsion to another over long stretches of historic time, the mystery of a boiling sun incessantly compressing hydrogen into helium to warm our planet throughout geologic time, and the torch of knowledge held out to us by de la Rue and Secchi, to carry forward towards the unknown future.

This photograph is the celestial embodiment of lovely words by modern poet-philosopher Anthony Liccione:


Her complexity is a glorious fire that consumes, while her simplicity goes unapproachable. But if one takes time to understand her, there is something beautiful to find, something simple to be loved.



And so we come to the end of this brief consideration of an image that is a simplicity itself, but through the avenues of printing, computer science and social media speaks to us of science, invention, travel, astronomy, art, adventure, history, chemistry, and photography.       How poetic.




[1] This photograph is to be found in the book The Invention of Photography: The First Fifty Years (pp82-3), and is in the possession of the Royal Astronomical Society, London.  Public domain. Please note: I have been trying to work out the writing at the bottom; so far I have “2nd of totality shows the  ____ _____ after the ____, _____ had been ________. Not very enlightening.  If you know, please let me know!
[2] Charles Vignoles (1860). Observations to accompany the Map of the Shadow-path thrown by the Total Eclipse of the Sun on the 18th July, 1860, across the North-Eastern Part of Spain. London: Longman, Green, Longmans and Roberts.  p. 37
[2] There is a great photograph of Warren de la Rue and his team on Getty images.
[3] In 1860 there weren’t fast food restaurants on every corner: “…the traveller will do well to provide himself, before he leaves his hostelry in the morning, with some of the “provend” so much insisted upon by that experienced traveller in Spain; and the Englishman should take care not only to carry his tea, but his tea-pot and tea-kettle. Even at the best places people have to wait a terribly long time for their meals, unless ordered some hours beforehand.”[Vignoles p37]
[4] Littmann, Espenak and Wlcok (2008) Totality: Eclipses of the Sun. Oxford Press pp 71-2
[5] T. Frederick Hardwich (1861). A manual of photographic chemistry, including the practice of the collodion process. London: John Churchill, New Burlington Street.
[4] Used via copyright provisions of Encyclopedia Brittanica,
[6] Giorgio Abetti. (1960)  Father Angelo Secchi: A Noble Pioneer in Astrophysics. Osservatorio di Arcetri.….8..135A&defaultprint=YES&filetype=.pdf

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2 responses to “A honey sun

  1. Barbara Becker

    April 26, 2017 at 9:50 am

    Sabrina — I believe the handwritten caption to the first “golden” eclipse photo reads: “2nd of totality shows the second epoch after the telescope had been disturbed”. I confess that the online image of the handwriting does not have sufficient resolution to make out the writing with any certainty — if you have a higher resolution image of the caption, that would be helpful. But I base my suggestion on De la Rue’s description of the images in the text of his Bakerian Lecture. De la Rue commented that changing the photographic plates necessarily resulted in a period of vibration in the apparatus.

    • Sabrina Bleecker Caldwell

      April 27, 2017 at 9:13 am

      Hello Barbara,

      I was so pleased to get your comment – I have been puzzling over that caption and was keen to hear from others on the topic. Your thoughts are well reasoned and even referenced! Thanks!



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