Clusters and Nebulae. 207 



CLUSTERS AM) NEBULA. — DOUBLE STARS.— 



OCCULTATIONS. 



BY THE EEV. T. W. WEBB, A.M., E.K.A.S. 



The rapidly- shortening days, however we may regret the loss 

 of out-door pleasures, bring their compensation to the astro- 

 nomical student in the increased opportunities of searching 

 for nebulse, and discovering the footsteps of the Creator's 

 glory in his more distant and, at any rate, less conspicuous 

 works. To these, therefore, we shall now re-conduct our 

 readers, enlarging, at the same time, our list of Double Stars, 

 which has long remained in a stationary condition. 



We begin with an object so intrinsically marvellous, that 

 we can but regret that so few amateurs are likely to be in 

 possession of the means of developing its structure. As in 

 many other cases, however, it will be interesting merely to 

 look at that which more fortunate observers are permitted to 

 look into. They, too, in turn, will have their own regret that 

 they are unable to look through a wonder, the true nature of 

 which is, notwithstanding, in all probability inaccessible to 

 mortal gaze. This is 



29. The Great Spiral Nebula in Canes Venatici. 51 M. 

 To find this, we must first get the bright star at the tip of the 

 Great Bear's tail, r\ Ursce Majoris, alias Al Kaid (sometimes 

 called Benetnasch). Nearly 2° (of arc, not of R.A., which 

 makes a material difference in these circumpolar regions) p 

 this, lies a 5-mag. star, 24 in Canes Venatici, or simply 24 

 Canum, the plural form sufficiently indicating that it does not 

 belong to either Canis Major or Minor, sjp this, we shall 

 notice an open triangle of much smaller stars, and just p the 

 star at the S. angle (or 2° s, a little p, from 24 Canum), a 

 finder of 1 J -inch aperture will show a dull and feebly, visible 

 patch. Powers of 30 and 65 upon 5| inches show a double 

 nebula in contact, the larger one about four times the size of 

 the smaller ; each possessing a sharp nucleus of nearly equal 

 intensity. With steady gazing, the larger nebulosity shows 

 some feeble traces of convolutions or indistinct irregularities. 

 A power of only 111 proved already too high for its faint and 

 misty light. Messier, the discoverer in 1772, failed, as might 

 be expected, in doing more than perceiving the duplicity and 

 contact, and measuring the central distance, y first perceived 

 that one of the nuclei was surrounded by a distant halo or 

 glory, which, in fact, forms the exterior edge of the larger 

 nebula, as seen in ordinary telescopes. His son detected and 

 drew a "partial subdivision of this ring into two branches 

 throughout its sf limb," and thought it might resemble our 



