AAS 205th Meeting, 9-13 January 2005
Session 44 HAD III: Catalogs, Surveys and Ancient Observations
Oral, Monday, January 10, 2005, 2:00-3:30pm, Pacific Salon 1

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[44.03] Vacancies in the Heavens: Caroline Herschel and the Discovery of Dark Nebulae.

C.J. Lada (CfA)

Late in the spring of 1784 William Herschel was at the eyepiece of his monstrous 20-foot telescope shouting out to Caroline Herschel, his younger sister and observing partner, counts of stars as they passed though his field of view. At one point during the observing session there was a long moment of silence, after which Caroline heard William exclaim: “Heir ist wahrhaftig ein Lock im Himmel!” (“Here is certainly a Hole in the Heavens”) These words mark the telescopic discovery of dark nebulae. William reported this discovery in a brief subsection of a paper to the Royal Society in 1785. He believed that what he observed was an opening or hole in the distribution of stars. He apparently did not attach too much greater significance to this observation and never discussed it any subsequent publications. However, Caroline appears to have guessed that this observation held a potentially greater significance. Indeed, fifty years after the initial observation, she encouraged her nephew John Herschel to confirm William’s observation with the refurbished 20-foot telescope that he had just erected in South Africa. After this she proceeded to compile first catalog of dark nebula which she extracted from the large body of telescopic observations made by William with her assistance over the many years with the 20 foot telescope. It wasn’t until the early twentieth century that the work of Barnard and Wolf conclusively demonstrated that these startling vacancies in the sky were true astronomical objects-- dark obscuring nebulae and it took another half century until astronomers proved them to be the birth sites of all stars and planets in the galaxy, amply confirming Caroline’s intuition concerning their importance in the pantheon of astronomical objects.

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