Characteristic Features of Solar Prominences

Abstract

view Abstract Citations (42) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Characteristic Features of Solar Prominences Pettit, Edison Abstract Spectra of prominences.-An objective-grating spectrogram taken at the eclipse of June 8, 1918, by Anderson and Babcock shows the prominences without the overlapping flash spectrum. The results of measures on this spectrogram are given in a table of wave-lengths and intensities. These data show that, with two exceptions, all the lines in the flash spectrum brighter than 30 on S. A. Mitchell's scale are found in prominences; 14 lines fainter than intensity 30 are also found, all of temperature classes ITT-V. "Metaffic" prominences show all the lines in Mitchell's table brighter than i~, ex- cept those of ionized barium. Save in brilliancy there is probably no real difference between the spectra of common and metallic prominences. Forms of prominences.-Prominences may be divided into five classes: (i) active, (2) eruptive, (~) spot, (~) tornado, and (~) quiescent, each of which is illustrated. An examination of prominences of classes i, 2, and 5 in projection on the disk, combined with their appearance at the limb, shows them to be in form like sheets of flame standing on edge. The larger prominences are connected with the chromosphere oniy at inter- vals a]ong the lower edge through columns like the roots of a tree. Dimeiisions.-The thickness of prominences varies from 6ooo to 12,000 km. The length as projected on the disk is seldom less than 6o,ooo km or greater than óoo,ooo km. A height of 50,000 km is quite common, and eruptive prominences have been known to reach a height of two-thirds of a solar diameter. The volume of a prominence is often of the order one hundred times that of the earth. Masses of prominences.-After suitable correction of the observational material, the work of Pannekoek and Doom shows that an ordinary prominence has a hydrogen con- tent of 2 X i~'~ atoms per cubic centimeter. The calcium content is negligible. On this basis a representative prominence io,ooo km thick, 200,000 km long, and 50,000 km high would have the mass of a cube of water 15 km on an edge. The mass of the largest prominence on record, that of May 29, 1919, would be about four times as much. Distribution of the elements-Comparison of both Ha spectroheliograms and drawings made at the spectroheioscope in Ha with spectroheliograms in K2 shows that the forms of prominences in these two lines are essentially the same. An examination of the eclipse spectrum extends this conclusion to other lines. The absence of certain streamers and faint clouds from the Ha observations may be due to instrumental conditions. There is, however, some reason to suppose that the effect may be real, since an electrical field would produce just this result. Disturbances in the corona about prominences are per- haps evidence that the Ca+ atoms attract the electron streams in the corona. Motions in eruptive prominences .-T he principle of uniform motion modified by sud- den increases in velocity already found was tested (i) by a review of the best examples already given, (2) by an examination of new material published by other observers, (~) by new material obtained for the purpose, and (~) by examining the impartiality of the measurements. The conclusion is that this principle of motion in eruptive prominences is real. Light-pressure-If light-pressure is operative in producing the motion, the Doppler effect which separates the absorption lines of the prominence from the corresponding absorption lines of the photosphere should also produce a separation of the hydrogen and calcium atoms. No separation of this kind was observed, however, in the eruptive prominence of August 6, 1931. Expansion of eruptive prominences and the corcnal density-gradienL-It is shown that the density of the prominence of August 6, 1931, followed the law d R~, and also that 1 Contributions from Ihe Mount Wilson Observatory, Carnegie Institution of Washing- ton, No. 451. Publication: The Astrophysical Journal Pub Date: July 1932 DOI: 10.1086/143396 Bibcode: 1932ApJ....76....9P full text sources ADS | Related Materials (1) Reprint: 1932CMWCI.451....1P