Radial movement in sun-spots

Abstract

DIBPLLOEME~S of the lines of hydrogen and aaloium in tho neighbourhood of sunspots, indioating violent in the line of sight, is a common chmaoteriatio of spot distubanoes. 8noh phenomena are frequently obsoned during periods of aative o h q e in spot development, or during the genesis of a spot. Them line-,&if-t~ mrely affeot the ~peotro of other el em ant^ than thorn of the hlgher ohmmosphere. In very violent mfbursta, in addition to the hydrogen and oaloium lines, those of Ee, Mg, Na, and somo of the enhanoed lines of F e are oooosionally seen to be affeoted, but to s, much leas extent than thore of H and Oa. The dieplacemente may be either an inorease or a deoreme of wavelength , and may amount to several ingatrbrn mitr, indicating movements of spproaoh or reoesaion of sevaral hundred kilometem per seoond. These movements are seldom mamtained for more than a few minutea at a time, and are ~8~8lb to be found 1n the immehate neighbourhood of spots, r m l y within the nmbml aroa. Recently line-shifts of quite mother oharaoter have beon photographed hero. Those are apporontly permanent, d e o t a very large proportion of the Brauuhofor absorption lines, and aro only found in the penumbra of spots. In the oouree of meaeurement of a largo number of spot speotrum plat00 obtained hero, it was noticod that tho position of the lines of tho true umbra1 speotrum seem usually to bo almost entirely ailaffeiIeated by motion in the line of sight. It is true that very slight displaooments towards tho violot appear to be indicstod in a series of nmssures of eome of the best pletos, but the &mount of the displeaemcnt (about 0.004 i/l is aoaroely larger than the lLnlts of error of measurement. I n these plates the scale is about 1A = 0 67 mm., and any movements of the sol~r gases of less than 3 l a. per seoond would be too small for deteotion. I n some spectra obtained this year, in the fourth and 61th ordere of a 3 2 inoh grating: in whioh the soale is 11 = 1-0 to 2 mm., the displaoement of thelines i n the umbrm of spots is dill barely meaanrsbl~, bnt very obvlous displacements sro found in the penwnbrm ; and thia shift turns out to be of o. maat interesting abaraoter, and icl apparently a oonstsnt feature of all epob. That it should have escaped deteotion hithGrto is moat surprising, considering the high diepersion now employed in all spot e p e o t m work.