Our Astronomical Column

    Abstract

    THE NEBULA, MESSIER 8 (G.C. 4361).—Dr. Tempel draws attention to the different appearance presented by this large nebula at the present time from that depicted in Sir J. Herschel's drawing made at the Cape of Good Hope in 1836–37, which he considers can only be explained on the assumption of a shifting of the whole nebula with respect to the stars by reference to which it was delineated at the Cape, or by great changes in the nebula itself. The case will be worthy of attention, because it appears Sir J. Herschel's drawing was made with much care, as he says “every attention has been paid to exactness.”The whole area occupied by the nebula, so far as he could trace its convolutions, is stated to be about one-fifth of a square degree. The relative positions of the stars in and near it, to the number of 186, were ascertained by differential observations with 9 Sagittarii; “from these measures skeleton charts were then constructed, and being divided into convenient triangles, the nebula was worked in upon them.”A drawing made under these circumstances might certainly be expected to represent its actual features, and it appears to be given with confidence by Sir J. Herschel. Dr. Tempel, observing with the large Amici-telescope at Arcetri, near Florence, finds that the reference stars entered in the Cape drawing are still as they then were, with some insignificant variations of position or brightness; but the difference of the details of the nebula as projected on these stars, from those shown by Sir J. Herschel, are so marked as to leave, in Dr. Tempel's opinion, no other explanation than is suggested above. Prof. Schiaparelli, to whom Dr. Tempel had forwarded his own delineation of the nebula for comparison with that made at the Cape, remarks, after twice examining it:—“Je dirai tout-de-suite, qu'il m'aurait été impossible de reconnaître la næbuleuse avec le seul dessin de J. Herschel.” The nebula is figured on Plate I. in the Cape observations; the description will be found at p. 14. Probably Mr. Ellery, who, as was stated last week, is still occupied with new drawings of Sir J. Herschel's figured nebulæ, may be able to express an authoritative opinion with respect to the supposed changes in this object.

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    Our Astronomical Column . Nature 16, 522–523 (1877). https://doi.org/10.1038/016522b0

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