A little ramble through 19th century astronomy - Change in a Nebula

The variations in the appearance of a nebula to different eyes and with different telescopes make it very difficult to establish a physical change, though observers in the southern hemisphere hold that such has certainly taken place in the case of the nebula in which the remarkable variable star eta Argus is involved. Prof. Holden has lately collected the evidence bearing on the question of change in another remarkable nebula—that known, from its peculiar form, as the Greek omega—and from a careful comparison of the relative positions of the nebula and accompanying stars, in drawings made at different times, he infers that, while the stars and one portion of the nebula show no change, another portion appears to have moved considerably.

This may be a veritable change in the structure of the nebula, or it may be a case of proper motion; in either case the fact, if well established, would be of great interest. The drawings examined were: —Herschel’s in 1837, Lamont's in 1837, Mason's in 1839, Lassell’s in 1862, and finally two by Trouvelot in 1875, with different telescopes, one of 6 inches aperture, and the other the Washington refractor of 26 inches.

 Although Prof. Holden does not consider the evidence conclusive as yet, he hopes it will be deemed sufficient to lead to a careful study of this nebula, for future reference, being undertaken—a work for which accurate draughtsmanship is above all things necessary, most of the difficulties of such investigations arising from want of skill in delineating such difficult objects, for which the trained eye of an artist is most desirable

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