SCIENCE- GOSSIP. 



2 5* 



CHAPTERS FOR YOUNG ASTRONOMERS. 



By Frank 0. Dennett. 



(Continued from p. 59.) 



JUPITER. 



Next to the Moon, Jupiter is the most easily 

 studied object in the solar system, having an 

 apparent diameter of from 30" - to 46" - 0. Its 

 appearance in the heavens is so striking that 

 under favourable conditions it will throw evident 

 shadows on the Earth. The real distance separating 

 the Earth from Jupiter when in opposition is 

 about 390,000,000 miles, so that its magnitude must 

 be very great. Its equatorial diameter is 88,000 

 miles — more than eleven times that of the Earth — 

 whilst 1,389 globes the size of this world would 

 together only equal Jupiter in volume, and have a 

 surface 124 times that of our planet. The density 



that time such spots have been frequently seen, 

 some of them being very persistent, and others 

 very evanescent. 



After the middle of the nineteenth century, and 

 especially subsequent to the advent of the silver- 

 on-glass reflectors, attention was directed to the 

 colours which were apparent on different parts of 

 the disc. The brighter band surrounding the 

 equatorial regions of the planet was often observed 

 to have a tint like yellow ochre or pink. The dark 

 belts bounding this band were at different times 

 seen to be copper-coloured, slaty-blue, or chocolate 

 hue. The polar regions sometimes showed tints of 

 delicate blue or green. But to see these colours at 

 all well, telescopes of considerable aperture were 

 necessary. 



Fig. 1 shows the'planet as seen by the writer on 

 April 19th, 1898, at 10.55 P.M., with a 9^-inch 

 Newtonian, by the late Mr. G. With. It shows the 

 nomenclature of the various parts of the disc 



Pig. 1. Jupiter, April 19th, 1898, 10.55 p.m. 1 



of its contents is, however, less than one-quarter 

 that of the Earth, the result being that 317 globes 

 the weight of ours would just balance the planet 

 Jupiter. The mean rate of the Eartn in its orbit 

 is 1,100 miles a minute ; but Jupiter only travels 

 483 miles in the same time. When the first tele- 

 scopes were turned on Jupiter his large size was 

 noticed ; but some years elapsed before it was 

 discovered that, instead of being circular, the 

 polar diameter was about one-sixteenth less than 

 the equatorial — a consequence of its rapid rotation, 

 which as early as 1665 Cassini found to take place 

 in about 9h. 56m. 



Long before this, in 1635, it had been noticed 

 by Zuppi and Fontana at Naples that there were 

 dark grey markings on the planet — belts, as they 

 were called— running parallel to each other across 

 the disc. Traces of these may be just seen with a 

 1-inch achromatic telescope, or even less, bearing 

 a magnifying power of about 40 diameters. Nothing- 

 more was specially noticed until 1664, when Hooke 

 observed a dark spot on one of the belts. Since 



(1) a, South Polar Region ; b, Southern South Temperate 

 Band ; c, South Temperate Band ; n, South Tropical Belt : 

 E, Equatorial Zone.- p, North Tropical Belt : g, North Temperate 

 Band ; ii, Northern North Temperate Band ; I, North Polar 

 Region. 



Pig 



Jupiter, July 28th, 187S, 1 a.m. 



adopted by the Jupiter Committee of the British 

 Astronomical Association. 



In the summer of 1878 attention was called to a 

 remarkable red spot which had appeared in the 

 bright band south of the south tropical belt. 

 Fig. 2 represents the first drawing of this object 

 made in England, at 1 a.m. on July 28th. 1878. 

 This object led to- a complete revolution in the 

 method of observing Jupiter. The marking, which 

 at first was thought to be new, has been traced 

 back, and appears to be identical, in the light 

 of subsequent study, with objects seen at intervals, 

 so long since as 1869, if indeed it was not the 

 object seen by many observers at still earlier dates. 

 In 1869 it presented the appearance of an oval or 

 elliptical ring ; but at the time of its appearance . 

 in 1878 it was bright red, a colour which it re- 

 tained for a few years, but subsequently lost. The 

 spot was still to be seen in 1899, but it had 

 become very faint, and was only visible with a 

 good instrument in clear air. The writer only 

 suspected it once with a 3-inch aperture, but 

 the dim object is shown in Rev. T. E. R. Phillips's 

 beautiful drawing of May 6th, 1899. The length of 

 this notable spot was about 27,000 miles, and its 

 breadth about 8.000 miles. 



{To he continued.) 



