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An equally close examination of the spectrum of Betelgeux showed the predominance in it of the linear absorption of iron; but its characteristic flutings do not extend to the photographic region. Spectra of the second and third orders are for this reason not easily distinguished on the sensitive plate.
Espin, then in the course of the photographic survey carried on at Harvard College, that considerably over one thousand stars are at present recognised as of the family of Betelgeux and Mira, while about 250 have so far exhibited the spectral pattern of 19 Piscium. One fact well ascertained as regards both species is the invariability of the type.
A photographic research, made by Keeler at the Alleghany Observatory in 1897, convinced him that the linear spectrum of third-type stars of the Betelgeux pattern essentially repeats that of the sun, but with marked differences in the comparative strength of its components. Hydrogen rays are inconspicuously present.
Betelgeux, the bright star on Orion's right shoulder, denoted martial honours or wealth; Bellatrix, the star on Orion's left shoulder, denoted military or civic honours; Rigel, on Orion's left foot, denoted honours; Sirius and Procyon, the greater and lesser Dog Stars, both implied wealth and renown.
In yellow stars, such as Capella and Arcturus, the same rhythmical series was partially represented, but associated with a great number of other lines; their state, as regards ultra-violet absorption, approximating to that of the sun; while the redder stars betrayed so marked a deficiency in actinic rays that from Betelgeux, with an exposure forty times that required for Sirius, only a faint spectral impression could be obtained, and from Aldebaran, in the strictly invisible region, almost none at all.
As to the stars themselves, the presumption of their approximate uniformity in size and brightness has been effectually dissipated. Differences of distance can no longer be invoked to account for dissimilarity in lustre. Minute orbs, altogether invisible without optical aid, are found to be indefinitely nearer to us than such radiant objects as Canopus, Betelgeux, or Rigel.
Of two, however those of Betelgeux and Aldebaran he was able to furnish detailed and accurate drawings.
Thus, the splendid Canopus, Betelgeux, and Rigel can be inferred, from their indefinite remoteness, to exceed our sun thousands of times in size and lustre; while many inconspicuous objects, which prove to be in our relative vicinity, must be notably his inferiors. The limits of real stellar magnitude are then set very widely apart.
Two of the stars, Betelgeux and Alpha Cygni, gave no certain sign of any perspective shifting; of the rest, Procyon, with a parallax of 0·334", proved the nearest to our system. At the mean distance concluded for these ten brilliant stars, the sun would show as of only fifth magnitude; hence it claims a very subordinate rank among the suns of space.
The spectra of Sirius and Castor, instead of being delicately ruled crosswise throughout, like that of the sun, were seen to be interrupted by three massive bars of darkness two in the blue and one in the green; the light of Pollux, on the other hand, seemed precisely similar to sunlight attenuated by distance or reflection, and that of Capella, Betelgeux, and Procyon to share some of its peculiarities.
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