Letter | Published:

Large Sunspot Group of February 1935

Nature volume 135, pages 309310 (23 February 1935) | Download Citation



ALTHOUGH the sunspot group referred to in NATURE of February 16 (p. 260) was not specially large, it was of interest because of its very rapid growth. Spectro-heliograms in K2, 3, 2 light were secured through thin cloud at the Solar Physics Observatory, Cambridge, on February 5, 6 and 7. On February 5 the group is shown on a plate exposed from 12h 25m 18s to 12h 26m 51s, and as the formation was near the centre of the disc, it must have been recorded very near 12h 26m 5s. As no spot was shown on the Greenwich photograph at 10h, this fixes the time of formation of the spot to within 2½ hours. On the spectroheliogram the feature was very small. On February 6 there is evidence of very rapid growth ; preceding and following spots are clearly shown, and the group extended over about 10° of solar longitude. February 7 still further expansion was shown, with an extent of flocculus of about 15° longitude. Any other observations of this spot group on February 5 during the hours 10h to 12h 30m would be welcome as affording information of the details of development.

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  1. Solar Physics Observatory, University of Cambridge. Feb. 16.

    • C. P. BUTLER


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