SOLAR PROMINENCES IN MOTION^ 



By Robert R. McMath 

 Director of the McMath-Hulhert 01)servatory of the University of Michigan 



[With 6 plates] 



The study of the nearest star to our earth, the sun, is probably of 

 great antiquity. This study, begun by earliest man, has now evolved 

 from the simplest of visual studies and observations into a field of 

 science which demands more and more intricate and expensive ap- 

 paratus and the services of skilled scientists all over the world. 

 With this evolution has come a separation of the general study into 

 branches. For instance, Dr. C. G. Abbot, of the Smithsonian Insti- 

 tution, is the acknowledged authority on the solar constant, which 

 deals with the radiation received daily by the earth from the sun. 

 Of course, other men at other institutions also study this important 

 aspect of solar phenomena, but their particular branch of specializa- 

 tion may lie in another direction. 



At the McMath-Hulbert Observatory, which is located at Lake 

 Angelus, Pontiac, Mich., we are interested most particularly in those 

 solar phenomena which are in some way connected with that part 

 of our sun which we call the chromosphere. This is, perhaps, a loose 

 definition, but we shall use it here for the sake of simplicity. 



When one looks at the sun through a piece of heavily smoked 

 glass, he sees what the astronomer calls the photosphere. Surround- 

 ing the photosphere is a shell of gas, similar to an atmosphere, which 

 is called the chromosphere. This chromosphere is about 8,000 miles 



^ The ninth Arthur I^ecture, given under the auspices of the Smithsonian Institution, 

 January 16, 1940, consisted principally of the unusual motion pictures taken at the 

 McMath-Hulbert Observatory. In all, about 4,000 feet of 35 mm. motion-picture film 

 were shown to the audience, accompanied by comments and explanations by Dr. McMath. 

 This tyr>e of lecture does not lend itself readily to reproduction on tlie printed page, so 

 we publish herewith his general remarks, accompanied by several plates made from the 

 films shown during the lecture. For more information in regard to the instrumentation 

 and the techniques employed, the reader Is referred to the Publications of the Observatory 

 of the University of Michigan, with particular reference to vol. 4, pp. 53-73, 1 932 ; vol. 5, 

 pp. 103-117, 1934 ; vol. 6, pp. 43-44, 1934 ; vol. 7, pp. 1-5G, 1937 ; and pp. 191-208, 1939. 

 With Dr. Edison Pettit, of the Mount Wilson Observatory, Dr. McMath has published 

 several papers dealing with the scientific a8i)ect9 of the motion pictures shown at the 

 lecture. These papers have appeared in the Astrophysical Journal, 1937 and 1939, and 

 occasional notes in the Publications of the Astronomical Society of the Pacific. 



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