. The Bell System technical journal . otatesabout the optic axis of the telescope with time. This rate varies withthe declination of the object and other factors and in our case it ranged THE CORONA VISER 257 within a degree or two of 7° per hour. Thus by taking a series ofphotographs over a period of several hours it was possible to determinedefinitely whether or not the image in question was associated withthe sun or with the apparatus. In addition to this test, for the prom-inences, there was the spectrohelioscope at hand by which a directcomparison could be made. Another test applied to th
. The Bell System technical journal . otatesabout the optic axis of the telescope with time. This rate varies withthe declination of the object and other factors and in our case it ranged THE CORONA VISER 257 within a degree or two of 7° per hour. Thus by taking a series ofphotographs over a period of several hours it was possible to determinedefinitely whether or not the image in question was associated withthe sun or with the apparatus. In addition to this test, for the prom-inences, there was the spectrohelioscope at hand by which a directcomparison could be made. Another test applied to the prominenceimages was furnished by their color. A red glass filter, such as theSchott RG 2 which has a cut-off just below the Ha line, reduced thegeneral glare level by about 30 times whereas its reduction of the lightof the prominences which is a maximum at this wave-length was notnearly so great. Results The prominences shown in Fig. 5 are among the first of which goodimages were obtained. Seven photographs were taken of them be-. Fig. 5—•Prominences taken with red filter on Feb. 21, 1938. tween 16^ 58°^ and 19^^ 11°^ on February 21, 1938, some inwhite light and the others with the red filter in front of the particular photograph was taken in red light; those taken in whitelight were of considerably less contrast. Figure 6 is another one of the many prominence photographs thathave been taken with the apparatus. These are the prominences thatwere present around the sun at 18^ 30™ on October 31, was also taken with the red filter. Figure 7 shows a pair of bright prominences photographed in whitelight on October 3, 1938. Figure 8 shows a jet or flare in the corona that was photographedon October 18, 1938. It is one of 11 photographs that were taken 258 BELL SYSTEM TECHNICAL JOURNAL
Size: 1609px × 1552px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
