Photography’s contribution to the science of Astronomy
170 years ago, Sir John Herschel exposed the first glass plate photograph. The subject was the 40 foot telescope used by his father, William Herschel. The elder Herschel discovered Uranus in 1781. And in collaboration with his sister, Caroline, he observed numerous comets and thousands of nebulae and star clusters. To make his photograph, John Herschel used a silver chloride solution. But the processing method was so time-consuming and tedious that it wasn’t widely adopted.
In the 1800’s, the idea of using glass plates to take pictures was under development by many pioneers of photography. Louis Daguerre accidentally discovered a method that used a thin layer of silver on a copper base. In 1840, John W. Draper took the first photograph of a celestial object, a daguerrotype image of the Moon. As his technique improved, Draper was able to capture more detail of craters and other features on the lunar surface.
It became clear that photography could revolutionize the science of Astronomy. Instead of relying on their hand-drawn sketches and log notes, astronomers could use photographs to collect precise records of the position, brightness, spectra and features of celestial objects. In 1850, director of the Harvard College Observatory, William Bond and photographer J. A. Whipple took the first picture of a star, Vega. But, as wonderful as daguerrotypes were, their application was limited because they lacked the sensitivity needed to capture fainter objects.
Frederick Scott-Archer introduced a new method to photograph dim objects in 1851. But, it was based upon a wet plate process that after preparation had to be used immediately. Although more sensitive, wet plates proved to be an obstacle. Before beginning a night of imaging, astronomers had to wait for wet plates to be readied. The hours of delay and potentially explosive mix of chemicals needed to use wet plates made them impractical.
While daguerrotypes and wet plates were successfully used to photograph the 1874 transit of Venus, the need for a new kind of photographic medium wasn’t met until a solution was offered by Richard Leach Maddox. His process used a dry gelatin silver-bromide preparation on glass plates. The dry plates offered many advantages. They didn’t have to be prepared on the spot or used immediately. Further improvements by Charles Bennett and George Eastman made dry plates more sensitive and easy to inexpensively mass produce. In 1880 Henry Draper, son of John W. Draper used dry plate technology to make a 51 minute exposure of the Orion Nebula.
While studying exposed glass plates at the Harvard College Observatory in the early 1900’s, Henrietta Swan Leavitt noticed that some stars pulsed with regular changes in brightness. By plotting a matrix of these stars and their brightness cycles she realized that they could be used to make distance estimates to remote celestial objects. These stars became known as the Cepheid variables.
Working at Mt. Wilson Observatory, Edwin Hubble recorded glass plate images of a spiral nebula in the constellation Andromeda. He located 13 Cepheid variable stars within the nebula. In 1924, using formulas based upon Leavitt’s work, he announced his landmark discovery that the Andromeda nebula is actually a separate galaxy far beyond the Milky Way.
A few years later, at the Lowell Observatory, Clyde Tombaugh used glass plates to conduct his photographic survey of remote areas beyond the orbit of Neptune. This effort lead to his 1930 discovery of Pluto.
Today astronomers use sophisticated electronic sensors like CCD arrays to record images of celestial objects. Along with X-ray, infrared, ultraviolet and radio telescopes, we are now able to peer beyond visible light into other parts of the electromagnetic spectrum. But, without the earlier contributions of glass plate photography many important breakthroughs in astronomy would not have been possible.
