United States or Italy ? Vote for the TOP Country of the Week !
Twenty-foot Michelson interferometer for measuring star diameters, attached to upper end of the skeleton tube of the 100-inch Hooker telescope. In the practical application of this method to the measurement of star diameters, the chief problem was whether the atmosphere would be quiet enough to permit sharp interference fringes to be produced with light-pencils more than 100 inches apart.
Finally, to mention only one more case, it was the Michelson-Morley experiment, made years ago with still another form of interferometer, that yielded the basic idea from which the theory of relativity was developed by Lorentz and Einstein. Made with the spectroheliograph, showing the immense vortices, or whirling storms like tornadoes, that centre in sun-spots.
To mention only a few of those that have helped to establish Michelson's fame, we may recall that our exact knowledge of the length of the international metre at Sevres, the world's standard of measurement, was obtained by him with an interferometer in terms of the invariable length of light-waves.
Cleveland, eyes upon interferometer grating and spectrophotometer charts, fingers flying over calculator keys, grinned as he turned toward Rodebush. "Just as you thought, Skipper; an ultra-band pusher. Shall I give him a little pull?" "Not yet; let's feel him out a little before we force a close-up. We've got plenty of mass. See what he does when I put full push on the projectors."
He was at that time at work on a special form of interferometer, designed to determine whether atmospheric disturbances could be disregarded in planning large-scale experiments. The principle of the method can be most readily seen by the aid of an experiment which any one can easily perform for himself with simple apparatus.
It was well along toward morning when he obtained in a test-tube a few drops of a colourless, odourless liquid. "My interferometer gave me a clue," he remarked, as he held the tube up with satisfaction. "Without the tell-tale line in the spectrum which I was able to discover by its use I might have been hunting yet for it.
Pease at Mount Wilson on April 15. As the mirrors of the interferometer were moved apart, the fringes gradually decreased in visibility until they finally disappeared at a mirror separation of 19.6 feet. Adopting a mean wave-length of 5600/10000000 of a millimetre for the light of Arcturus, this gives a value of 0.022 of a second of arc for the angular diameter of the star.
It now remains to make further measures of Betelgeuse, especially because its marked changes in brightness suggest possible variations in diameter. We must also apply the interferometer method to stars of the various spectral types, in order to afford a sure basis for future studies of stellar evolution.
The 20-foot interferometer designed by Messrs. These take the place of the two holes over the object-glass in our experiment. After this the course of the light is exactly as it would be if the mirrors M2, M3 were replaced by two holes over the 100-inch mirror.
He then referred to the work already in progress on Mount Wilson, but anticipated "that atmospheric disturbance will ultimately set the limit to what can be accomplished." Measures with the interferometer show its angular diameter to be 0.047 of a second of arc, corresponding to a linear diameter of 215,000,000 miles, if the best available determination of its distance can be relied upon.
Word Of The Day