74 



HA RD WICKKS SCIENCE- G OS SIP. 



identified by the examination of star charts. In 

 the course of a short time, the distance between the 

 planets and the stars seen in their proximity will 

 exhibit a change. For some unexplained reason 

 Mr. Barnard had some suspicions about this speck of 

 light, he therefore continued his observations on the 

 nights of September II, 12, 13, 14, and 16, and 

 found that, when this little body was visible, it was 

 always somewhere near Jupiter. It was not one of 

 the fixed stars, for it travelled with, and round, 

 Jupiter. This tiny body proved to be a fifth satellite, 

 never going beyond 67,000 miles from the surface of 

 its primary (about one-fourth of the distance of the 

 nearest of Galileo's satellites), and travelling round it 

 in an elliptic orbit, in a period of about 11 hours 

 57 minutes — about two hours longer than it takes the 

 planet to rotate once on its axis. Few telescopes in 

 the world will show this fifth satellite ; it has been 

 seen by only three instruments in America and the 

 same number in Europe, none having a smaller 

 aperture than twenty-two inches. Our knowledge 

 of both the Martian and Jovian systems has thus, 

 been enlarged by American observers ; the two 

 moons of Mars having been discovered at the 

 Washington Observatory in 1877. The diameter of 

 this newly discovered — but probably very old — 

 satellite of Jupiter is so small that it cannot be deter- 

 mined by observation. 



We must remember that Jupiter is placed at 

 a very great distance from us — though this distance 

 is a mere nothing as compared with that of what 

 we, in the present state of our knowledge, consider 

 the nearest fixed star. When Jupiter is nearest to us 

 it is about 400,000,000 miles distant, whereas the 

 distance of a Centauri, the nearest fixed star, is such 

 that light travelling at the rate of about 189,000 miles 

 every second, takes 4J years to come from it to us. 

 The difficulty of seeing this little moon is due, not 

 merely to its small size, but also to the fact that its 

 distance from its primary never takes it away from 

 the glare of the planet, and, moreover, it does not 

 shine by its own inherent light, like the stars. Our 

 knowledge of it is, therefore, exceedingly limited. 

 It is known that the attraction of Jupiter has diverted 

 comets from their paths ; can this be the remains of a 

 comet that has been entangled in his system, and 

 has had its original course altered so as to revolve 

 round him ? 



The discovery of Jupiter's fifth satellite was made 

 by means of the largest refracting telescope in the 

 world. Another very important discovery had been 

 made eight months previously by the aid of what one 

 might almost call the smallest in the world, a mere 

 pocket telescope. So much, as has been rightly said, 

 depends on the man at the little end of the 

 instrument. 



On a few occasions, what are called " new," or 

 " temporary, 1 ' stars have been observed — stars, which 

 for some reason or other have shone more or less 



brightly, and for a longer or shorter time — where 

 previously no star was known to exist. In order to 

 detect these, unless they burst suddenly into great 

 brilliancy, like the celebrated temporary star which 

 was seen from November, 1572, to March, 1574, a 

 considerable acquaintance with star charts, and the 

 actual appearance of the heavens, is necessary. In 

 this manner, and by the aid of only a small glass, 

 Dr. Anderson, of Edinburgh, had gained such a 

 knowledge of the positions of the stars in the 

 constellation Auriga, that he one night saw a star 

 that he was able to say he had never noticed before, 

 and which was not marked on the excellent star maps 

 he used. He unfortunately allowed some days to 

 elapse before he made his discovery known. He then 

 adopted the unusual course of sending a notice of it 

 anonymously, on a postcard, to the Royal Observa- 

 tory at Edinburgh, nor did his name transpire till 

 some little time afterwards. Immediately on the 

 receipt of his postcard, on February 1, 1892, the 

 news therein contained was communicated to the 

 principal observatories of the world, and the im- 

 portance of the discovery was soon manifest. Nova 

 Aurigae at once became an object of diligent and 

 careful examination. The telescope showed that its 

 brightness varied in a peculiar manner, .but beyond 

 this the instrument indicated nothing. Further 

 discoveries were, however, made by the spectroscope. 

 By means of prisms or a grating, that is, a surface of 

 glass or speculum metal on which are ruled a very large 

 number of exceedingly fine lines, many thousands to 

 the inch, the light proceeding from a star or other 

 luminous body can be analysed and its nature 

 determined, as well as the amount of the approach 

 or recession of the body, if it is in motion. The 

 light proceeding from Nova Aurigae, when .spread 

 out into a little strip in the spectroscope, exhibited 

 peculiar appearances, the interpretation of which is 

 not yet quite settled. Various theories have been 

 propounded, but the matter is still sub jiidice. On 

 August 20, the object presented the appearance of a 

 small, bright nebula, with a stellar nucleus of the 

 tenth magnitude. Not a clear night passes without 

 photographs of some parts of the heavens being 

 taken, and on some of these plates being afterwards 

 examined, it was found that the image of the star had. 

 impressed itself on some plates taken at the Harvard 

 College Observatory, Boston, twelve times between 

 December 10, 1891, and January 20, 1892. By 

 comparing the Harvard plates with some taken at 

 Heidelberg, it would appear that the Nova increased 

 from below the eighth magnitude to above the fifth, 

 between December 5 and December 10, 1891. 



Had not Dr. Anderson known the positions of the 

 stars in Auriga so well, had he not been such an 

 accurate and painstaking observer, the discovery of 

 this wonderful object would not have been made by 

 him, or at any rate it might have been delayed 

 beyond January, 1S92. 



