Much before the word “corona” struck panic and fear in people owing to its association with the virus and the disease, it was more popularly used elsewhere… in eclipses. For the corona seen around the moon during a solar eclipse is certainly a sight to behold.
The origin question
While we now know almost all about it, one of the greatest astronomical questions of the 19th Century concerned these mysterious prominences that appeared beyond the edge of the moon during the solar eclipse. While the bright red flames around the moon forming the prominence had been observed, the question remained as to what were its origins. Was the phenomenon terrestrial, lunar or solar?
It was seeking answers to this question that English astronomer and chemist Warren de la Rue set sail from Plymouth Harbour in England aboard the HMS Himalaya , borrowed from the Royal Navy for the purpose. Knowing that the important solar eclipse was scheduled for July 18, 1860, de la Rue set out on his mission with his team to observe it from a particular place 11 days earlier.
De la Rue, born in Guernsey (an island in the English Channel) in 1815 and educated in Paris, France, began his journey in astronomy by producing detailed pictures of nearby celestial bodies. Apart from his observation of detail that led to brilliant drawings of the sun and the moon, his real talent came out when he started applying photography to astronomy.
Telescope meets camera
His exertions towards bringing together two important technologies resulted in the Kew photoheliograph. This powerful new tool designed by de la Rue combined a telescope and a camera and was the first such instrument built for the specific purpose of photographing celestial objects.
Equipped with his photoheliograph, de la Rue took along with him an entire photographic laboratory aboard the HMS Himalaya . Sailing through the Bay of Biscay to Bilbao in Spain, de la Rue and his party of four assistants, interpreters and porters were accompanied by their families for this adventure. They set up their observatory in the small village of Rivabellosa.
On the morning of July 18, cloudy skies threatened to derail the expedition, but the weather cleared just in time for the eclipse. Even before the sun began to hide behind the moon, de la Rue and his crew were training the photoheliograph, which was positioned for the task.
Totality captured
Even though they were unsure of capturing an image of totality, in the end they managed two such shots. With a total of over 40 photographs, they were able to see the solar eclipse (of 1860) with greater detail than ever before. In de la Rue’s own words, these images “depicted the luminous prominences with a precision as to contour and position impossible of attainment by eye observations”.
To determine the origins of the red flames visible at the edges of the moon during the eclipse, de la Rue devised a simple idea. If these features were Earth (terrestrial) or moon-based, observations from different places of the same event should be different. If, on the other hand, these were solar in origin, then the observation site shouldn’t impact the results.
Photography for astronomy
By comparing photographs of the eclipses from two different places, de la Rue was able to firmly establish that these flames were indeed of solar origin. The origin question about these features, now known as prominences, had finally been solved.
De la Rue was able to show that photography could be employed to resolve a scientific problem in astronomy. Thus, apart from answering an important astronomical question, de la Rue’s method set the tone for the future as photography continues to play a pivotal role in unravelling the secrets of celestial bodies.
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The many hues of de la Rue
De la Rue might be best known for his famous eclipse expedition of 1860, but there was more to the man than just that.
After returning from Paris and joining his father’s print business, de la Rue developed one of the first envelope-folding machines along with English engineer Edwin Hill. This mechanical system to make envelopes was displayed at London’s Great Exhibition of 1851.
While U.S. inventor Thomas Edison is often credited for the incandescent lamp, de la Rue had in fact solved the scientific challenge confronting the problem nearly 40 years before him. By using thin, high-resistance platinum (high melting point) filaments that were sealed in a vacuum, de la Rue was able to achieve brightness and delay burnout in his light bulbs. His choice of expensive platinum (as opposed to Edison’s cheaper carbon filament) and the inability to achieve good vacuum paved the way for Edison’s success.
