Abstract
A PLANETARY nebula in R.A. 18h. 25.2m. and Dec. — 25° 13′ was discovered at the Harvard College Observatory on the evening of July 13. A second nebula was found on the following evening in R.A, 18h. 4.3m. and Dec. — 28° 12′. Both, but particularly the first, are only minute, and can be with difficulty distinguished from stars, except by their spectra. The discovery was not the result of accident but of a search with a direct vision prism inserted between the objective and eyepiece of the 15-inch telescope. A star appears as a coloured line of light, while a planetary nebula forms a bright point, and is recognised instantly in sweeping. Many hundred or thousand stars can thus be examined very rapidly, and a single nebula picked out from among them. This method promises to add very greatly to the list of known planetary nebulae, which now number about fifty. Probably a systematic search for these objects crossing a considerable part of the heavens will be made at this Observatory. Our knowledge of that distribution will thus be greatly increased, and we shall know that their absence in certain parts of the sky is not due to an omission to look for them. Any planetary nebula as bright as a twelfth-magnitude star would probably be detected by the method proposed. Bright lines or other peculiarities in the stellar spectra will also be looked for.
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PICKERING, E. Two New Planetary Nebulæ . Nature 22, 327–328 (1880). https://doi.org/10.1038/022327a0
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DOI: https://doi.org/10.1038/022327a0