Solar Eruptions and Radio Fade-outs

Abstract

THE associated phenomena of a bright hydrogen eruption on the sun on December 3 and a radio fade-out, described in NATURE of December 12, p. 1017, had an interesting sequel 27 days later. On December 30, the sun was under continuous observation with the spectrohelioscope at the Royal Observatory, Greenwich, from 9h 45m to 12h 55m U.T., and at first attention was concentrated on a region near the central meridian which showed signs at 9h 45m of having been recently active. At 10h 30m, a bright eruption began rapidly to develop there and lasted until about llh. At 10h 57m, on turning to another part of the disk, a very bright and extensive hydrogen eruption was seen to have begun at a position about 55 ° west of the central meridian in latitude 22 ° north; in about 20 minutes this bright eruption had spread southwards to about latitude 14 ° north, so that the eruption when fully developed was spread over a distance of about 60,000 miles in latitude. (This active region was nearly identical in position with the region that was active on December 3.) It is shown by a whole disk spectroheliogram, taken in hydrogen light (Ha.) by Mr. Evershed at his observatory at Ewhurst, that at 10h 34m this second and larger eruption on December 30 had not begun, though another spectroheliogram taken at llh 20m (after information had been received from Greenwich) shows the eruption near its full development. The most probable time of the beginning of the eruption, derived by extrapolating an intensity curve given by photometric measures made at Greenwich after 10h 57m, is about 10h 50. The declining stages of the eruption were relatively slow, and by 12h 50m the streaks of emission were of the normal brightness of ordinary flocculi.