Betelgeuse
the name given to a fixed star of the Orion constellation, also known as the Alpha Orionis, whose diameter, according to measurements made by Professor Albert A. Michelson, of Chicago University, is slightly more than three hundred times that of the sun, and nearly as large as that of the orbit of the planet Mars. Professor Michelson, in 1920, by means of a device for determining the actual diametrical size of a star, calculated that of Betelgeuse to be 260,- 000,000 miles. Compared with the sun in volume, this makes it 27,000,000 times as great, and if it could be placed as near to the earth as the sun, the planet would embrace the entire visible heavens. It is computed that it would take trillions of globes like the earth to equal Betelgeuse in size. The distance of this star from the earth is perhaps 150 "light" years, that is, the light which strikes the eye in looking up at Betelgeuse started on its journey from the star at the rate of 186,- 000 miles a second 150 years ago (from 1920). By Professor Michelson's device, it is believed that measurements of planets lost in space with invisible disks can be accurately determined with the aid of a simple formula. Astronomers incline to BETELGEUSE than the sun. The dimension created to Betelgeuse, indeed, presents the conception of celestial bodies of magnitudes hitherto unmeasured and almost beyond comprehension.
The size of Betelgeuse was determined by combining its approximate distance from the earth, which was known, and its angular diameter, which had to be ascertained by Professor Michelson. Angular diameter is not the same as real or linear diameter. In the case of a star it has to be known before the real diameter can be calculated. The angular diameter of any object (say a house) varies according to the distance from which it is viewed; the real or linear diameter remains the same, no matter at what varying distances a spectator sees it. Only the angular diameter (or the apparent diameter) is changed by the spectator changing his distance, and the farther off he stands the smaller the angular diameter becomes. The distance of Betelgeuse from the earth is approximately 1,070 trillion miles, from which dim point in the firmament is showed an angular diameter of 0.046 seconds, i. e., 46/1,000 of a second of arc, or, say, for round numbers, 1/20 of a second. The magnitude of this exceedingly small angle can be appreciated by the fact that it is roughly equal to that which would be shown by a pinhead at a distance of more than a thousand miles. To put an angular diameter of 1/20 of a second into miles, Professor Michelson had to combine it with the known distance of the star in miles, remembering that since an angular diameter of one second corresponds to a distance of 206,000 times the actual or linear distance of the object, an angular diameter of only 1/20 of a second must correspond to a distance of about 4,120,000 times the object's real diameter. The actual diameter of Betelgeuse was thus found to be approximately 260,000,000 miles by dividing the 1,070 trillions (the star's distance) by 4,120,- 000. This measurement could not be made by direct observation. The smallness of the star's image not only rendered such a measurement impracticable, but such effects as irradiation and twinkling obscured the star's definition and blended the edge of the image with the diffraction rings surrounding it. These obstacles have been overcome by the use of the "interferometer," a device whose feature is parallel and movable slits of known distances separating them in_a screen covering the viewing lens. By manipulating the slits the star's light becomes shed of the fringes, or interthe opinion that other fixed stars, seem-ference bands, which appear when the ingly small by reason of their distance instrument is focused on the star. As from the earth, are also vastly larger the slits are moved apart the fringes BETHAM-EDWARDS become finer and with their disappearance the angular distance of the source of light becomes ascertainable. In the apparatus used by Professor Michelson he substituted a system of reflecting mirrors for the slits, thus obtaining better results.