JUPITER 



3191 



JURASSIC PERIOD 



JUPITER, the "giant planet" and king of 

 the solar system, is the largest planet and the 

 fifth in their order from the sun. Its diame- 

 ter, 88,000 miles, is almost eleven times that 

 of the earth, its surface is 122 times and its 

 volume 1,355 times that of the earth. Its 

 density, however, is less than one-fourth that 

 of the earth. So while it would take more 

 than 1,300 earths to fill the space occupied by 

 Jupiter, it would take only 316 earths to equal 



JUPITER AND ITS SATELLITES 

 it in weight. If we could imagine a huge 

 balance with Jupiter in one scale pan, we 

 should have to place 316 earths in the other 

 to balance it. A man weighing 150 pounds 

 on the earth would weigh 400 pounds on Jupi- 

 ter. Next to the sun Jupiter is the largest 

 body in the solar system. Its mean distance 

 from the sun is 483,000,000 miles, over five 

 times that of the earth. 



Jupiter is easily recognized, since it is, next 

 to Venus, the brightest planet, and sometimes 

 it rivals that planet in brightness. When seen 

 through an opera glass or a small telescope it 

 appears slightly flattened, owing to the differ- 

 ence between its polar and equatorial diame- 

 ters. When seen through a large telescope 

 the planet presents a beautiful appearance. 

 The disk is marked with belts of different col- 

 ors which run parallel to the equator. The 

 outline is hazy, showing that the planet is 

 enveloped in an atmosphere of clouds and fog. 

 The light is brightest in the center and dimin- 

 ishes towards the edges, the side farthest from 

 the sun being darker than the other. In 1878 

 a great red spot, 30,000 miles long and 7,000 

 miles wide, was noticed and, until recently, this 

 was a prominent feature, but it is now very 

 dim. 



Jupiter turns upon its axis once in nine hours 

 and fifty-five minutes, so its day is less than 

 one-half of our day. Its year, however, is 

 nearly twelve of our years. Its axis is but 

 slightly inclined to the plane of its orbit, there- 

 fore, the change of season must be slight (see 

 SEASONS) . 



Satellites. Jupiter is accompanied by nine 

 moons, four of which have been discovered 

 since 1892. The fifth satellite was discovered 

 by Prof. E. E. Barnard of the Lick Observa- 

 tory, and a sixth and seventh by C. D. Per- 

 rine of the same institution. The eighth 

 satellite was discovered in 1908, and the ninth 

 in 1914. The eighth has the peculiarity of 

 revolving around the planet in the opposite 

 direction from the others. Romer made his 

 great discovery of the velocity of light by 

 observation of the eclipses of the satellites of 

 Jupiter. See LIGHT. 



It is generally believed that Jupiter is still 

 in a heated and partially gaseous condition, 

 and that it is not a solid body like Mars and 

 Venus, but resembles the sun, except that it 

 gives off much less light. W.F.R. 



See PLANET, for comparative sizes of the 

 planets and distances from the sun ; see SUN, for 

 comparative sizes of the sun and the planets. 



JURA, joo'ra, a mountain range extending 

 from northeast to southwest along the borders 

 of Switzerland and France, forming a high 

 plateau between the Rhine and the Rhone 

 rivers. The German Jura begins at the Rhine 

 and extends about 300 miles to the main val- 

 ley. South of the Rhone the chain is known 

 as the Jura Alps, merging there with other 

 branches of the great Alps range. Towering 

 peaks rise at intervals, and along the lower 

 elevations beautiful lakes are formed, the 

 largest being Lake Geneva, a famous resort. 

 The highest peaks are Reculet and Crete de la 

 Neige, both over 5,600 feet in altitude. 



Mineral products are scarce for so moun- 

 tainous a country, although iron, copper and 

 salt are mined in fair quantities. Marble, ala- 

 baster and granite are quarried, and the valu- 

 able timber is a source of profit. Lausanne, 

 a beautiful city, lies on the southern slope of 

 the mountains. The two chief rivers having 

 their source in the chain are the Doubs and 

 the Ain, both French streams. The geologi- 

 cal formation is chiefly limestone, the range 

 giving its name to the Jurassic, or second 

 system in point of age of the geological periods. 



JURASSIC, jooras'ik, PERIOD, that divi- 

 sion of geologic time immediately following 

 the Triassic. The formations constitute what 

 is called the Jurassic System, and lie between 

 the Triassic below and the Cretaceous above. 

 The name is given because of the prominence 

 of the rocks in the Jura Mountains. In North 

 America Jurassic formations are found in Cali- 

 fornia, Oregon and, to a slight extent, in Alaska. 



