American Science

Abstract

IN the December number of the American Journal of Science and Art, Mr. Holden collates various observations, by the Herschels and others, on the trifid nebula M 20, discovered by Messier, June 5, 1764, who, however, gives no details concerning it. The result of the inquiry is to show (1) that from 1784, when Sir William Herschel first described it somewhat in detail, to 1833, the remarkable triple star observed in the nebula, was centrally situated between the three nebulosities; (2) from 1839 to 1877 the triple star was not centrally situated, but involved in one of the nebulosities (A). The idea that the triple star has a large proper motion being thought improbable, it is concluded that the nebula has undergone marked changes of position, or brilliancy, or both, during the period 1784 to 1877. The conjecture was thrown out by Sir John Herschel, that “perhaps this singular object has a proper motion.”