SOLAR FKOMIWKNCBS IN MOTION — McAIATB 125 



violent activity and break into whiplike filaments, which apparently 

 stream downward into the sun. Spectroheliograms such as plate 1, 

 G^ which are taken in the light of the broad K line of calcium, em- 

 phasize the bright markings and show a mottling of the entire disk 

 which, when projected, has the appearance of a troubled sea. The 

 difference in emphasis of hydrogen and calcium spectroheliograms 

 does not necessarily indicate a separation of the two gases in the 

 chromosphere, for it is possible to record the same features in both 

 spectral lines by proper spectrograph adjustment. This difference 

 does, however, afford a means of selecting certain details for examina- 

 tion by accentuatmg their appearance above that of surrounding 

 activity. Dark flocculi are more readily photographed in Ha, and, 

 consequently, this line is usually used to record their behavior. 



Plate 1, E^ which is an Ha spectroheliogram of the sunspot group 

 shown in Z? as a direct photograph, was selected from a record of 

 violent chromospheric activity which involved both the bright and 

 dark flocculi. The S-shaped bright flocculus below the large spot 

 very suddenly became more intense and began to expand. At the 

 apparent maximum brilliancy, a dark marking developed along the 

 center line, as shown in the frame reproduced from this point in 

 the record. Eventually, the entire flocculus darkened, disintegrated, 

 and disappeared. 



Actually, all details photographed on the disk show a high rate 

 of radiation and appear light or dark depending upon the relation- 

 ship of their radiation to that of their surroundings. When seen 

 against the disk, the high-level gas clouds, such as surround the spot 

 shown in plate 1, F^ are dark; but when we follow them to the edge 

 of the sun, as in {?, they show, in exposures timed to record disk 

 detail, as dimly lighted against the dark background of the sky. In 

 G we also can see in profile the general disturbance of the chromo- 

 sphere in the region of a sunspot. In this position, at the edge of 

 the sun, the high-level formations can be seen and photographed in 

 greater detail, and are called prominences. 



Kecurrent typical forms and behaviors of motion have been in- 

 cluded in Pettit's classification of prominences. More recently, some 

 new types have been revealed by the motion-picture records, and are 

 illustrated by the reproductions in plate 2. The first new type to 

 be discovered was the "coronal," so-called because its apparent origin 

 is somewhere high above the chromosphere in the region of the 

 corona. A shows such a streamer at about 150,000 km. above the 

 chromosphere, moving downward toward the sun. This streamer 

 was first barely visible at a higher level, and subsequent spectro- 

 heliograms show it moving along a trajectory that terminated in the 

 bright limb at a point above the sunspot. In this picture as well as 



