THE ERUPTIVE PROMINENCE OF SEPTEMBER 14, 1940

Abstract

An eruptive prominence was photographed by J. O. Hickox on September 14, 1940 with the 13-foot spectroheliograph on Mount Wilson using the Κ line of calcium. It will be the sixtysecond prominence in the catalogue1 of eruptive prominences for which velocities have been determined. When first photographed that morning at 14h 45m G.C.T. it was a class IIIc (sunspot) prominence, 130,000 km high and 190,000 km long, in latitude 26° S. It was then pouring into a nearly extinct sunspot group, Mount Wilson No. 6972, which was 15° beyond the west limb in latitude 17° S. This group had been inconspicuous during its transit across the solar disk. Although accompanied by a bright flocculus, no dark Ha flocculi were visible near it. When the prominence first appeared at the west limb on September 12 it was very active internally, but the principal features did not change appreciably during the day.2 On the morning of the 13th it was still unchanged except in minor details and was therefore not followed during that day. By the 14th it had developed greatly and when the routine program of observation had been completed it was already in the eruptive stage. The moving head K, Plate XXVIII, easily identified on the successive exposures, was measured on images of the spectroheliograms projected upon a milk-glass screen, with a scale of 2500 km per mm. It moved along a straight line which left the chromosphere at Ο directly beneath the original position of the prominence and was inclined away from the spotgroup, S, at an angle of 55° to the solar radius. The motion was measured along this inclined path. Only one eruptive prominence has been known to move along a more inclined path. It was observed on September 8, 1919 and moved at an angle of 57° to the vertical.8