Abstract
STEREOSCOPIC SPECTROHELIOGRAMS.—A remarkable pair of photographs of hydrogen (Hα) flocculi, showing a stereoscopic effect, have been forwarded to us by Prof. Hale. They were taken with a new grating spectroheliograph, used in conjunction with the 60-ft. tower telescope at Mt. Wilson, and exhibit the flocculi surrounding a large spot-group near the sun's west limb on August 7, 1915. The time interval between the two exposures was seven minutes, giving a separation of the two images due to the sun's rotation somewhat greater than Helmholtz's estimate of 1 for the minimum angular separation of two objects just sufficing for stereoscopic vision. The photographs show the structure of the flocculi in a way which at once recalls Langley's well-known representation of the minute details of the photosphere about a spot; and a long, dark flocculus, which afterwards appeared as a prominence on the west limb, is distinctly seen in relief. Photographs of this kind must necessarily be affected by changes in the actual details in the interval between the exposures, and by distortion arising from drift of the solar image, or from irregular motion of the spectroheliograph, during exposure; but Prof. Hale believes that with due precautions the stereograms will assist in clearing up some of the questions referring to relative levels. A check on the reality of the stereoscopic relief has been obtained by taking photographs of a globe having a roughened surface, turned through angles corresponding with the intervals between the solar photographs.
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Our Astronomical Column . Nature 97, 249 (1916). https://doi.org/10.1038/097249a0
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DOI: https://doi.org/10.1038/097249a0