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Large Sunspot Group

Nature volume 135, page 260 (16 February 1935) | Download Citation



A MODERATELY large sunspot group which formed on February 5 has attracted, for its size, an undue amount of notice in the daily Press. The group occupies about 800 millionths of the sun's hemisphere, and a spot of these dimensions will be no uncommon occurrence during the next six or seven years, as the sunspot cycle passes through its maximum in 1938. Actually, a larger group, occupying 1000 millionths of the sun's hemisphere, has already appeared since the last minimum in 1933. This group had its central meridian passage on April 21.9, 1934 (see the Observatory for February 1935, where an account of 1934 sunspot activities will be found). The present spot is, however, not without interest. No spot was detected on a photograph exposed at Greenwich on February 5 at 10h, but at llh a spectroscopic disturbance was seen in the spectrohelioscope, which seems to have been the genesis of the actual spot. On account of cloud, no photoheliogram was taken on February 6, and the spot appeared fully developed on February 7. The spot's latitude is 14° S., and it was born west of the central meridian. Its central meridian passage-if it survives-will take place on March 14 next. The spot is of such a size that it could just be seen by the naked eye if it was on the central meridian. Near the limb, where the spot appears foreshortened, a spot of this size would be invisible. It is interesting to note that the number of naked eye sunspots per annum follows the ordinary sunspot curve very closely, and that the 11-year cycle could well have been discovered by an observer provided only with a smoked glass-and a good climate.

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