110 



♦ KNOW^LEDGE 



[March 1, 1888. 



THE STARS OF OTHER TIMES. 



HERE is a strange charm in contemplating 

 the star-strewn heavens, with the thought 

 in remembrance that as the constellations 

 are now, so were they in all the past ages 

 over which history extends its survey, and 

 beyond them throigh the ages when man 

 himself had scarcely begun to exist as a 

 reasoning race, and in ages still more remote when this earth 

 was inhabited by millions ofliving creatures, but by none who 

 could think about the wonders surrounding them. Here and 

 there a few stars have changed in lustre ; new stars have 

 appea,red and old stars have vanished ; the swifter motions 

 of a few (including some of the chief brilliants of the 

 heavens) have carried them to new positions among the 

 star-groupings, but in the main the scene presented by the 

 star-strewn heavens now is the same which was presented at 

 the beginning of the Christian era, the same which Ptolemy 

 and Hipparchus surveyed, the same which the builders of the 

 Gi'eat Pyramid studied more than five thousand years ago, 

 the same which the first races of men contemplated with 

 slowly growing intelligence, the same on which the eyes of 

 all animal races must from time to time have been turned 

 during the millions of years which have elapsed since life 

 began upon this earth. 



Yet the aspect of the constellations, as seen from pai-- 

 ticular latitudes or positions on the earth in long past ages, 

 differed notably from their aspect as seen from such places 

 now, even though the actual configuration of the star- 

 groupings was the same. The constellations being carried 

 round the polar axis of the heavens by the diurnal motion, 

 take varying positions above the horizon of any latitude, 

 these positions depending upon the position of that axis, 

 which is coincident, of course, in direction with the axis of 

 the earth. And owing to the reeling, or gyration, of the 

 earth's globe, her axis is constantly changing in direction. 

 It is inclined about 2.3^° to a perpendicular to the plane 

 of the earth's path, and thus, neglecting slight changes in 

 the position of this plane, the points on the heavens to 

 which the earth's axis is directed — that is, the poles of 

 the heavens — travel in circles about 47° in arc-diameter 

 around the poles of the ecliptic, the period of circuit being about 

 2-5,868 years. This suffices, of course, to modify very largely, 

 in long periods of time, the aspects of the constellations, 

 themselves unchanging, as they are carried by the diurnal 

 motion across the sky. The pre-sent north pole of the 

 heavens, for example, which lies due north about 514° 

 above the horizon of London, w^as more than 47° from the 

 point in the star-sphere which was the north pole 12,934 

 years ago ; so that at that time the present pole-star (not 

 quite coincident with the north pole, but near it) was 

 cai'ried round the actual pole in a circle 94° in arc- 

 diameter, ranging from an altitude of 4° or 5° above 

 the northern horizon to an altitude of 81° or 82° above the 

 southern hoiizin. Not only have the movements and 

 positions of individual stars been thus modified, but the 

 positions of star-groupings, when most favourably situated 

 for observation, have been so modified as in many cases to 

 make it difficult for us to understand how men in old times 

 came to imagine resemblance between star-groupings and 

 various objects, animals or otherwise, where now no trace 

 of resemblance is suggested when, those star-groups are 

 studied as actually seen in the heavens. 



It has seemed to me that it would be interesting, and 

 might lead to results of considerable scientific and even 

 historic importance, to prepare a chart by means of which 

 the exact aspect of the heavens as seen at any hour of any 

 night in the year, from any given latitude, at any epoch in 



the past or future, might be readily determined. All the 

 maps hitherto constructed to illustrate the effects of the 

 precession of the equinoxes have shown no more than 

 the movement of the north pole of the heavens around the 

 north pole of the ecliptic. What seemed wanted was a map 

 from which the position of the equator at any epoch might 

 be obtained at once ; and thence, by simple constructions, 

 any further information which might be required respecting 

 the appearance of the night skies at different hours and 

 seasons at that epoch. 



The accompanying map is the northern map of a pair 

 which I have drawn for this purpose. (The southern map 

 is already engraved, and will appear next month.) It is 

 .simply a stereographic map of the heavens to a distance of 

 100° around the north pole of the ecliptic as centre. Thus 

 the Zodiacal zone is the outer zone — 20° wide — of the map ; 

 and the circle 23,V in arc-distance from the centre of the 

 map represents the apparent path of the pole of the northern 

 heavens. 



The map being on the stereographic projection, it is a very 

 simple matter to mark in the equator (and colures if needed) 

 for any given epoch. Thus, suppose the epoch to be 276 

 B.C., or 21.j6 years before the date of the map (1880). 

 The precession of the equinoxes in 2156 years (one-twelfth 

 of 25,868 years, the precessional period) amounts to 30° 

 (one-twelfth of 360°). Thus, as the precessional motion 

 carries the crossing-point of the equator on the ecliptic to 

 meet the sun, we must take a point 30° in advance of the 

 present crossing-point ( r ), or to the first point marked « 

 in the map. This and the opposite point on the ecliptic, 

 marked iij;, are the crossing-points of the equator on the 

 ecliptic in the year 276 B.C. Then on the longitude circle 

 through r (that is, the radial line in the map to the point 

 on the ecliptic midway between the two just determined), 

 we measure off 23.5° towards the pole of the ecliptic — that 

 is, towards the centre of the map. A circle swept through 

 the point thus determined and the two crossing points 

 determined before, shows the position of the equator in the 

 year 276 B.C. This circle is shown by a dottecl arc in the 

 accompanying map. The corresponding position of the 

 north pole of the heavens at that time is shown on the 

 circle indicating the path of the pole, 30° in longitude from 

 the present position of the pole. The nearest visible star 

 is the 5th magnitude star 4 tlrsa^ Minoris. (The stars 4, 5, 

 (i and y of the Little Bear, doubtless formed the true Dog's 

 Tail — y marking the tip of the tail — not, as is commonly 

 said, the stars now forming the constellation Ursa Minor, a 

 group which can in no sense be likened to a dog's tail, 

 whereas the group of four stars very well might. This 

 Dog's Tail was the veritable polar-star group of the time of 

 Hipparchus ; and the name Kunosoura, or Dog-tail, served 

 well to indicate the pole of the heavens, though perhaps few 

 who use its modern form. Cynosure, and siieak of a centie 

 of attraction as " the cynosure of every eye," are aware of 

 the real meaning and orisin of the expression. 



In the map there is also shown the position of the equator 

 in the time of the building of the Great PjTamid, some 

 3350 years before the Christian era. (The positions of the 

 pole in 3350 b.c. and 2170 B.C., equi-distant, as the map 

 shows, from a Draconis, serve to explain why for awhile 

 the later date was accepted as that of the building of the 

 Great Pyramid. But now there Ciin be no doubt that the 

 earlier date is the true one ; for Egyptology and the astro- 

 nomy of the Great Pyramid are brought by this date into 

 agreement, where;is the date 2170 B.C. is wholly inconsistent 

 with the Egyptian records by which the dates limiting the 

 dynasty of Cheops, Chephren, and the rest, have been 

 indicated.) 



The position of the equator as thus assigned for the time 



