467 



KDooiledge & Seientlfie flems 



A MONTHLY JOURNAL OF SCIENCE. 



Conducted by MAJOR B. BADEN-POWELL, F.R.A.S., and E. S. GREW, M.A. 



Vol. III. No. 20. 



[new series.] 



JULY, 1906. 



SIXPENCE NET. 



CONTENTSSee page V. 



Holes in the Heavens. 



By J. E. Gore, F.R.A.S. 



There are many dark spots in the Milky Way which 

 seem to be openings or holes in that wonderful zone 

 of stars. These dark spots or "coal sacks," as they 

 are also called, seem to have been first noticed by 

 Pinzon, in 1499. They were also described by Lacaille 

 in 1763. 



The most remarkable of these spots is the well- 

 known "Coal Sack " near the Southern Cross. It is 

 of roughly oval or "pear-shaped " form, about eight 

 degrees in length by five degrees in width, and forms 

 a conspicuous object in the sky of the southern hemi- 

 sphere. It is completely surrounded by the nebulous 

 light of the Milky Way, which is here of considerable 

 brilliancy. The bright stars a and ji Crucis — the brightest 

 stars of the Southern Cross — nearly touch its south- 

 eastern edge. It contains only one lucid star within 

 its boundaries. With reference to its northern border, 

 Sir John Herschel says : " The transition from rich 

 Milky Way to almost complete darkness is here very 

 sudden." It is, however, by no means devoid of faint 

 stars. On a photograph taken in 1891 by Mr. H. C. 

 Russell, at the Sydney Observatory, numerous very 

 small stars are visible, but there are several spots which 

 seem to be completely void of stars, and absolutely 

 black. One of these remarkable holes is near /3 Crucis, 

 and another near a Crucis. 



There are other remarkable " coal sacks " in the 

 Milky Way. A long, narrow, dark spot runs from a 

 Centauri, for several degrees towards the north-east. 

 There are several in Scorpio, one of larger size be- 

 tween ij and f Cygni, and one south of a Cygni. 



Examined with a telescope, the Milky Way shows 

 many examples of small coal sacks; and some mav be 

 seen with even a good jjinocular field glass. One night 

 when Sir William Her.schcl was examining a part of 

 the Milky Way closely east of the globular cluster 

 80 Messier, which lies between i' and a- Scorpii, he 

 suddenly exclaimed to his sister — the famous Caroline 

 Herschel — " Hier ist wahrhaftig ein Loch im Himmcl " 

 (Here, truly is a hole in the Heavens). It was an ab- 

 solutely black vacuity, about four degrees in width, 

 perfectly frtx; from any stars, and especiallv remarkalile 

 owing to its proximity to one of the richest globular 

 clusters in the heavens. Closelv south of Herschel's 



dark "hole" just mentioned, Professor Barnard has 

 photographed a great nebulous region surrounding the 

 stars p Ophiuchi and 22 Scorpii.* This photograph 

 shows several dark lanes in what seems to be at least 

 a comparatively thin sheet of stars, and this distin- 

 guished astronomer thinks "it is certain that these 

 stars are at the same distance as the nebula, for they 

 form part of it." With reference to the Milky \\'ay in 

 general, he thinks that the stars comprising it are 

 " comparatively very small bodies, and that thev con- 

 sequently differ vastly in point of size, at least, from 

 the ordinary stars of the sky." If this be so, and the 

 evidence seems to point in this direction, it would 

 follow that their distance from the earth is not so great 

 as their faintness would lead us to imagine. In his 

 Cape Observations, Sir John Herschel gives a list of 49 

 spots in the southern hemisphere " totally devoid of any 

 perceptible star." But probably photography will 

 reveal the presence of some faint stars in these dark 

 spots. 



Closely east of the star e Ophiuchi is a "dark 

 chasm," which passes south and west of that star, and 

 there are several other dark " lanes " and holes clearly 

 visible on the photograph taken by Professor Barnard 

 at the Lick Observatory. 



Another small black spot was observed by Barnard 

 a little north-west of the star ■> Sagittarii. This seems 

 to have been previously seen by Trouvelot, who says : 

 " C'est comme un sac a charbon en miniature, ou 

 une ouverture de la Voie lactee a travers laquelle la 

 V'ue penetre au dela de oc grand assemblage d'etoilcs." 



.\ little south-east of a Cephii, a photograph by 

 Barnard shows a ring of nebulous light, with a com- 

 paratively dark interior, at least the stratum of stars 

 filling the rings seems pierced by several holes. 



The "key-hole" openings in the great nebula sur- 

 rounding the variable star ?; .-\rgus is a remarkable 

 feature of that wonderful nebula. A little south of this 

 hole there is a " kidney bean " shaped opening, shown 

 in Sir John Herschel's drawing in the Cape Observa- 

 tions. This opening is visible on a photograph taken 

 by Sir David Gill in March, 1892. The photograph 

 confirms the accuracy of Herschel's drawing, and 

 shows that the opening is in all probability a real 

 hole through the surrounding nebulous matter. 



In the region round the star 12 Monocerotis there 

 is a remarkable nebula of irregular shape, somewhat 

 resembling in its general character the great nebula 

 in the " sword " of Orion. Dr. Roberts, describing a 

 photograph he took of this nebula, says : " Some re- 

 markable tortuous rifts meander through the nebulosity 

 on the north preceding half of the nebula; their margins 



• The rings round the briehter stars io the photograph are due 

 to a photographic eft'ect, and do not exist in the sky 



