Abstract
AN interesting contribution to the investigation of the sun's rotation by the spectroscopic method has been made by Mr. J. B. Hubrecht in an extended discussion of a series of plates taken by him with the McClean equipment at Cambridge in June, 1911. The photographs in question are unique, inasmuch as in place of the usual comparisons at opposite points of the limb, they compare the spectra at points 900 apart, at intervals of 150 completely round the sun. By this arrangement the velocities in the two hemispheres may be separately derived, and Mr. Hubrecht concludes that at the period of these observations the velocities were greatest in the northern hemisphere. Thirty lines, belonging to seven elements, and including four enhanced lines, were measured, and no departure from average results was found for any of them. There was, however, a distinct diminution of the indicated Velocity with increase of wave-length, for which no definite explanation can yet be given. In relation to heliographic latitude, the results are remarkable as showing uniform angular velocity from 15° N. to 15° S., and, following the usual decline to higher latitudes, a slight increase between latitudes 6o° and 75°. The deduced angular velocities as a whole are also considerably smaller than those derived at Mt. Wilson, and the equatorial velocity is assigned the correspondingly low value of 185 km. per second;
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References
Annals of the Solar Physics Observatory, Cambridge. Vol. iii., Part i. The Solar Rotation in June, 1911, from Spectrographic Observations made with the McClean Solar Instruments. By J. B. Hubrecht. Pp. 77. (Cambridge: At the University Press, 1915.) Price 9s. net.
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The Sun's Rotation 1 . Nature 97, 184–185 (1916). https://doi.org/10.1038/097184b0
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DOI: https://doi.org/10.1038/097184b0