83 



SOME NOTES ON JUPITER DURING HIS OPPOSITION 



OE 1876. 



Et a. D. Hirst. 



lEead before the IRoz/al Society of N.S.W., 2 Angnst, 1876.] 



I SUPPOSE that of all the members of our solar system, with the 

 exception perhaps of our satellite, the Moon, there is no object 

 that so soon engages the interest or more readily yields to the 

 scrutiny of the amateur astronomer, when, with his newly-acquired 

 telescope before him, he sets himself to investigate some of the 

 wonders of the heavens of which he has been hitherto altogether 

 heedless, or which at best have excited his idle curiosity as they 

 have met his gaze, than the giant of our planet-neighbours, 

 Jupiter ; and the reason of this a slight inquiry will, I think, 

 make obvious. 



Mercury, as far as we at present know the closest of our Sun's 

 attendants, is an almost hopeless object for even the possessor of 

 the finest telescope. His minute size, and in consequence of his 

 position his intense luminosity, prevent anything like details ever 

 being seen. Moreover, when in his most favourable position for 

 observation, which is when he is furthest from the Sun, we, from 

 his orbit being interior to the Earth's, see but half his disk illu- 

 minated. Therefore, to these unfavourable circumstances we 

 must attribute the title Mr. Webb has given him in his " Celestial 

 Objects" of a neglected subject. 



To Yenus much the same arguments apply. Being larger than 

 Mercury, and also nearer to the Earth, we certainly do see some- 

 what more of her ; but her brilliance baffles all satisfactory defi- 

 nition, and I think no well-accredited markings or details of any 

 sort have ever yet been accorded of this, to the eye most beautiful, 

 but in the telescope most disappointing, planet. 



Passing now to Mars, the first exterior planet to the Earth, we 

 see what neither of the interior two can ever show us — a full 

 round disk illuminated by the solar light ; and we have the 

 further advantage of our object being brought at favourable oppo- 

 sitions very near the Earth. Here we can see marks which no 

 very great stretch of imagination or analogy may lead us to 

 suppose as representing land and water, more especially as 

 adequate optical means enable us to descry white spots at his 



H 



