Abstract
A SIMPLE INTERFEROMETER. —Probably many people are under the impression that interferometer methods are only possible with very large instruments. This is undoubtedly the case where measurement of stellar diameters is in question. But a short paper by Mr. L. Richardson (Brit. Astron. Assoc. Journ., Feb. 25) describes an application of the method that is within the reach of all amateurs. This is a cardboard screen covering the object-glass with a number of parallel openings cut in it, the width of the closed spaces being made equal to that of the open ones. The card can be turned by strings from the eye-end about an axis in its own plane through its centre, and the amount of tilt read on a scale made of millimetre paper. Each star then shows a central image, and a series of diffraction images on each side diminishing in brightness. Turning on Castor (for example), the card is tilted until the distance between the principal and first diffraction image is equal to that between the two stars of the binary. The tilt of the card then gives a very good measure of the angular distance between the stars. Four measures of Castor give distances 4.57″, 4.56″, 4.54″, 4.59″. Since the images are short spectra, there is a liability to personality in the measures, but a single observer can obtain accurate relative results.
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Our Astronomical Column. Nature 115, 582 (1925). https://doi.org/10.1038/115582b0
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DOI: https://doi.org/10.1038/115582b0