Over 150 glass plate photographs of the moon, stars, and solar eclipses were recently rediscovered in the basement of the the Niels Bohr Institute (NBI) in Copenhagen. Astronomer Holger Pedersen described in a report from NBI that he’d gone down to the basement to make a cup of tea and “noticed some cardboard boxes from the Østervold Observatory. They had been moved there when the observatory was shut down many years ago. The boxes were full of cartons, so I took them up to the office to take a closer look at them.”
What he discovered was an essential forgotten resource of what he calls “astronomy archaeology.” When photography was established as a medium in the 19th century, it provided an objective way to record the night sky. In 1840, John W. Draper in New York took what is believed to be the first photograph of the moon from a rooftop observatory in Greenwich Village, and its use in astronomy expanded in the following decades. The NBI photographs date back to 1895, when the Østervold Observatory telescope was completed. Astronomers can look at a glass plate of a lunar eclipse, for instance, and compare the craters to the moon we see today.
“The plate collection may have been taken to the Niels Bohr Institute — more specifically: to the Rockefeller Building, part of NBI — when the Copenhagen Observatory staff was resettled in 1996, but we have no record of that,” Pedersen told Hyperallergic. Since then, the boxes sat in a basement storage room, until about six months ago when that space was needed for computer equipment. The boxes, as well as quite a bit of “junk,” as Pedersen describes it, moved to the tea kitchen.
“It was here, that some two months ago, I could not control my curiosity, and thus saved the boxes from a grim destiny,” he explained.
Mindy Weisberger, who reported the story for LiveScience, spoke to Michael Shara, a curator at the American Museum of Natural History (AMNH), who noted that photographs like these can sometimes be our only recording of the sky in a particular time and place. In a recent episode of Shelf Life, the AMNH’s behind-the-scenes video series, Shara discusses how the half a million glass plates at Harvard University, for instance, provide a valuable view of the night sky in the 19th century.
“Among the plates that I cherish the most is a series of photographs of the planets, from Mercury to Saturn,” Pedersen said of the NBI images. One is a 30-second exposure of Mercury from May 10, 1896, “taken the same day as a British amateur astronomer, Henry McEven, made one of the most detailed drawings of its surface features.”
Researchers are still sorting through and scanning the plates, which date back 120 years, all made by exposing emulsion to light. Discoveries so far include photographs of binary stars; a 1912 plate of the star Arcturus in the constellation Boötes; a 1921 plate of the star Deneb in the constellation Cygnus; and an April 26, 1957 plate of the Comet Arend-Roland. There are also plates from other telescopes, including a 1950 exposure from the large Schmidt telescope at Mt. Palomar (now the Samuel Oschin telescope) in California.
“But first prize goes to the copy-plate from the total solar eclipse expedition to Sobral, Brazil, in 1919,” Pedersen stated. The image by British astronomer Arthur Eddington provided important evidence for Albert Einstein’s theory of general relativity, something which was hard to prove. The bending of the sun’s light was visible in the eclipse, supporting Einstein’s description of gravitation from large objects. A few rare copies were made, of which the Copenhagen copy is one. “Come 2019, we will surely see it on exhibit,” Pedersen said. In the meantime, the NBI astronomers will continue to time travel to the past through the plates, and glimpse the sky captured a century ago.
Read more about the rediscovered glass plate photographs at the Niels Bohr Institute.