Abstract
THE large sunspot reported on p. 156 of last week's issue was easily seen with the naked eye at about the time of central meridian passage on January 18. The maximum area of the spot was more than 3,000 millionths of the sun's hemisphere ; the spot is, therefore, one of the largest half-dozen spots recorded at Greenwich since 1875. As already reported, a magnetic storm was recorded at Abinger, beginning on January 16, 22½ hr. A second and larger disturbance developed rapidly on January 22 after 5 hr.; between 9 hr. and 10 hr. a range of 56' in declination occurred, while that in horizontal force was 600γ. This range in H.F. had not been exceeded at Greenwich since the magnetic storm.of May 17, 1921, but the maximum of the present period of disturbance had not been reached. On January 25 (a day after the big sunspot had disappeared over the western edge of the sun) a sudden commencement began at about noon and developed to a remarkable degree. The great aurora which followed is described above. A telephoned account of a preliminary examination of the Abinger magnetic traces stated that large movements of the recording magnets began at 17 hr. and were particularly marked between 20 hr. and 21½ hr.; the disturbance died down about 3 hr. on January 26. The total ranges during the disturbance were approximately 2·1° in declination, 1,000 γ in H and 550 γ in V. The storm is probably unequalled in the Greenwich records since that of September 25, 1909. As already stated, the big sunspot had passed off the disk on January 24 and there is no other unusual spot at present visible
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The Recent Sunspot and Magnetic Storms. Nature 141, 192 (1938). https://doi.org/10.1038/141192b0
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DOI: https://doi.org/10.1038/141192b0
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