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    SPECTRUM OF THE ORION NEBULA.—A full account of the photographs of the spectrum of the Orion Nebula, which were taken with Mr. Lockyer's 30-inch reflector at Westgate-on-Sea in 1890, has just been published in the Philosophical Transactions (vol. 186 A, p. 73.) Four hydrogen lines more refrangible than K are shown on the photographs, and in all 54 lines have been recorded. The line near wave-length 3730, first discovered by Dr. Huggins, is a very strong line, and among other prominent lines, is the well-known chromospheric line at wave-length 4471. It is shown that many of the principal lines are coincident with bright lines photographed in the spectrum of P Cygni at South Kensington, and with bright lines in planetary nebulæ and bright line-stars photographed by Campbell and Pickering, so that a close connection of these bodies is established. Other tables show a close relationship between the bright lines of the nebula and the dark lines in the so-called Orion stars, of which Rigel and Bellatrix are typical examples. The following are the conclusions to which the investigation has led: (1) The spectrum of the nebula of Orion is a compound one, consisting of hydrogen lines, low temperature, metallic lines and flutings, and high temperature lines. The mean temperature, however, is relatively low. (2) The spectrum is different in different parts of the nebula. (3) The spectrum bears a striking resemblance to that of the planetary nebulæ and bright-line stars. (4) The suggestion, therefore, that these are bodies which must be associated in any valid scheme of classification is strengthened. (5) Many of the lines which appear bright in the spectrum of the nebula, appear dark in the spectra of stars of Groups II. and III., and in the earlier stars, of Group IV.; a gradual change from bright to dark lines has been found. (6) The view, therefore, that bright-line stars occupy an intermediate position between nebulæ and stars of Group III. is greatly strengthened by these researches.

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