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Photographs of Two Great Southern Galaxies

1946; Institute of Physics; Volume: 58; Linguagem: Inglês

10.1086/125822

1538-3873

John C. Duncan,

History of Science and Natural History

On the night of Sunday, September 2, 1945, conditions on Mount Wilson were remarkably favorable for astronomical photography. Saturday night had been partly cloudy, and on Sunday morning there was an unseasonable shower. At sunset on Sunday the sky was largely overcast and a rain squall was visible near the coast, 35 miles west ; but the clouds had begun to disperse by nine o'clock, and during the remainder of the night, although there were occasional clouds, the sky between them was clear and the seeing was superb. The Observatory had just received from the Eastman factory a consignment of new 103aO plates which combine high speed with remarkable fineness of grain. On this favorable night, with these excellent plates, and with the 100-inch telescope, the photographs reproduced in Plates XIV and XV were made, showing two great nebulae in Sculptor, near the south galactic pole, which rise to only a moderate altitude for observers in the United States. The exposures, though much shorter than has been customary for such faint objects, could not have been much longer at that low altitude without accumulating a detrimental amount of sky fog. NGC55 (a 0h 12*5, & -39° 30', 1950.0; gal. long. 295°, gal. lat. -77°), Plate XIV, b, was described by Sir John Herschel in his Observations at the Cape of Good Hope (18341838) as very bright, large; much elongated; at least 25' long and 3' broad . . . .a long irregular crooked ray .... the following part is faint ; the preceding and shorter, trinuclear. A strange object. Herschel's drawing is reproduced in Plate XIV, a. Shapley and Miss Ames1 classify this nebula as a spiral, of total photographic magnitude 7 . 8, and they agree with the dimensions given by Herschel. Ori the original negative (Plate XIV, b), I find the dimensions 3' X 29', The spiral character seems doubtful to me, and from this photograph