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This actual measure of the diameter of Betelgeuse supplies a new and striking test of Russell's and Hertzsprung's theory of dwarf and giant stars. Just before the war Russell showed that our old methods of classifying the stars according to their spectra must be radically changed.
We won't shake it." While Morey took the time exposure, Arcot looked at the enlarged image in the telectroscope and tried to make angular measurements from the individual stars. This he found impossible. Although he could spot Betelgeuse and Antares because of their tremendous radiation, they were too close together for measurements; the angle subtended was too small.
If we use a mean value of 0.095 of a second for the parallax, the corresponding linear diameter comes out 21,000,000 miles. The angular diameter, as in the case of Betelgeuse, is in remarkably close agreement with the diameter predicted from theory. Antares, the third star measured by Mr. Pease, is the largest of all.
Vega burned, cobalt blue, in the heart of the Lyre. Colors, colors! Inside the atmosphere of Earth's night, the stars had been pale white sparks against black. Here, against the misty-pale swirls of cosmic dust, they burned with color heaped on color; the bloody burning crimson of Antares, the metallic gold of Capella, the sullen pulsing of Betelgeuse.
He picked out several blue-white and red giants he was sure he knew. That was Andromeda off there; that one was undoubtedly Orion no other contained so many 4.0 to 5.2 stars, beside the gigantic Rigel, Betelgeuse and Bellatrix. Good, he could fix all that in his mind well enough to draw it when he got back, and the Corps planetographers certainly would pin-point this system from those directions.
If it is actually a member of the Scorpius-Centaurus group, as we have strong reason to believe, it is fully 350 light-years from the earth, and its diameter is about 400,000,000 miles. Diameters of the Sun, Arcturus, Betelgeuse, and Antares compared with the orbit of Mars. Sun, diameter, 865,000 miles. Arcturus, diameter, 21,000,000 miles. Betelgeuse, diameter, 215,000,000 miles.
The precise hue is rather uncertain, but Aldebaran is not orange as Betelgeuse in Orion is, and no correct eye can for an instant confuse the colors of these two stars, although many persons seem to be unable to detect the very plain difference between them in this respect.
In fact, when the holes are moved apart to the full aperture of the 100-inch Hooker telescope, the interference fringes are still visible even with the star Betelgeuse, though its angular diameter is perhaps as great as that of any other star. Thus, we must build an attachment for the telescope, so arranged as to permit us to move the openings still farther apart.
To test the perfection of the adjustment, the telescope was turned to other stars, of smaller angular diameter, which showed the fringes with perfect clearness. Turning back to Betelgeuse, they were seen beyond doubt to be absent.
By comparing it with 0.047, the angular diameter of the star, we see that the linear diameter is about two and one-third times as great as the distance from the earth to the sun, or approximately 215,000,000 miles. Thus, if this measure of its distance is not considerably in error, Betelgeuse would nearly fill the orbit of Mars.
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