Half-hours with the Telescope

I may note here in passing that Sir John Herschel's delineation of the northern portion of the Milky Way, though a great improvement on the views given in former works, seems to require revision, and especially as respects the very remarkable patches and streaks which characterize the portion extending over Cepheus and Cygnus. It seems to me, also, that the evidence on which it has been urged that the stars composing the Milky Way are (on an average) comparable in magnitude to our own sun, or to stars of the leading magnitudes, is imperfect. I believe, for instance, that the brilliant oval of milky light in Cygnus comes from stars intimately associated with the leading stars in that constellation, and not far removed in space (proportionately) beyond them. Of course, if this be the case, the stars, whose combined light forms the patch of milky light, must be far smaller than the leading brilliants of Cygnus. However, this is not the place to enter on speculations of this sort; I return therefore to the business we have more immediately in hand.

Towards the east is the square of Pegasus low down towards the horizon. Towards the south is Scorpio, distinguished by the red and brilliant Antares, and by a train of conspicuous stars. Towards the west is Bootes, his leading brilliant -- the ruddy Arcturus -- lying somewhat nearer the horizon than the zenith, and slightly south of west. Bootes as a constellation is easily found if we remember that he is delineated as chasing away the Greater Bear. Thus at present he is seen in a slightly inclined position, his head (marked by the third-magnitude star β) lying due west, some thirty degrees from the zenith. It has always appeared to me, by the way, that Bootes originally had nobler proportions than astronomers now assign to him. It is known that Canes Venatici now occupy the place of an upraised arm of Bootes, and I imagine that Corona Borealis, though undoubtedly a very ancient constellation, occupies the place of his other arm. Giving to the constellation the extent thus implied, it exhibits (better than most constellations) the character assigned to it. One can readily picture to oneself the figure of a Herdsman with upraised arms driving Ursa Major before him. This view is confirmed, I think, by the fact that the Arabs called this constellation the Vociferator.

Bootes contains many beautiful objects. Partly on this account, and partly because this is a constellation with which the observer should be specially familiar, a map of it is given in Plate 4.

Arcturus has a distant pale lilac companion, and is in other respects a remarkable and interesting object. It is of a ruddy yellow color. Schmidt, indeed, considers that the star has changed color of late years, and that whereas it was once very red it is now a yellow star. This opinion does not seem well grounded, however. The star may have been more ruddy once than now, though no other observer has noticed such a peculiarity; but it is certainly not a pure yellow star at present (at any rate as seen in our latitude). Owing probably to the difference of color between Vega, Capella and Arcturus, photometricians have not been perfectly agreed as to the relative brilliancy of these objects. Some consider Vega the most brilliant star in the northern heavens, while others assign the superiority to Capella. The majority, however, consider Arcturus the leading northern brilliant, and in the whole heavens place three only before him, viz., Sirius, Canopus, and α Centauri. Arcturus is remarkable in other respects. His proper motion is very considerable, so great in fact that since the time of Ptolemy the southerly motion (alone) of Arcturus has carried him over a space nearly half as great again as the moon's apparent diameter. One might expect that so brilliant a star, apparently traveling at a rate so great compared with the average proper motions of the stars, must be comparatively near to us. This, however, has not been found to be the case. Arcturus is, indeed, one of the stars whose distance it has been found possible to estimate roughly. But he is found to be some three times as far from us as the small star 61 Cygni, and more than seven times as far from us as α Centauri.