ASTRONOMICAL NOTES

Hawera & Normanby Star, Volume LXXIV, Issue LXXIV, 23 August 1919, Page 5

ASTRONOMICAL NOTES

THE PLANET JUPITER

} (By L. A. Mac Donald.) Passing across the wide space which lies beyond the range of the inner Sfhal 1^ B°! ar SySt6m --"t what had long been regarded as a Buft y,ASert + in r,tile Planetary regions, ate to h?f 1' t ' I like T^ de^ts that without L Ud °? tJie carth > is ™* without its oases, its mysterious lights, its optical illusions. The princina darkness, which stretches from the S s °of at s ncr idf to the ««2™li limits ot the solar system is th> San?o/tn*e ter- th Ser onJ astern, because he is bigthan afl SE^T mT internal SetW t?, • + he-* planets Put togethei. Jupiter is very far avvav _h°™ v; he I™oll away than Venus, the beautiful evening star, and much further away than Mars, and considerably furth/r away than the innumerable asteroids which circle round the sun in orbits of vary ing eccentricity. The mean dist an ?e of the planet Jupiter from the sun ?s over four hundred aud eighty.?W million miles. Light which travels at the enormous speed of 185 000 mile* Jjy^f take from Jthirty mfive to fitty minutes in reaching us from the g ia? t planet. Jupiter is » most interesting object in a small telSseo^; expect, it i s oval m shape, the polar te i the eai; th- BroacF shadowy bands traverse the face of Jupiter; they are parallel to the equate/ and ara. of a cloudlike form; they change in shape and detail from night to ™ *-" i ? observer may observe a particular belt on one night, and on the succeeding night all traces of a belt of that description will be gone. Bright spots appear and disappear, tor the surface is one of continual change. Spots passing across the disc give an indication of how long the planet takes to rotate on his axis rsow we all know that the earth rotates in about 24 hours. Jupiter is over a thousand times larger than the earth, and he makes one complete rotation m a little less than ten hours. In the sky of Jupiter the sun would be seen perceptibly moving in the sky; and being a very small orb as seen trom the immense distance of Jupiter, the motion of the sun over the sky would be all the more .pronounced, there is every reason to believe that Jupiter's belts indicate the existence of a cloud-laden atmosphere. The dark streaks cannot be true cloudbelts. We have"to look on the reverse side of them as compared with the inhabitants of the planet, if there are any. What they would see as immense dark threatening clouds would appear as clouds of intense brilliancy to us, on account of our being on the side that intercepts the light of the sun. The dark belts are probably theglimpses we s?et of the real surface of the pTanet. The bright belts are bands of clouds which traverse the whole circumference of the planet. The storms which distract the atmosphere of Jupiter must be terrific. Storms are soiretimes very destructive on the earth; but they are really few in number, and occur after long periods of time. It is not so in the case, of Jupiter. His atmosphere is perpetually agitated, and sometimes—not infrequently—his disturbances can be clear- \ ly seen at a distance of four hundred million miles—the approximate, distance which separates the giant planet from the earth. The rapid rotation of the planet on his nxis is almost sufficient to account for the perturbed , state of bis atmosphere. The great red spot of Jupiter was about the only permanent marking on the planet: and this spot is now r almost out of sight.. It was first seen in 1878. For several years it looked like a rosy cloud: it w-as thought to be the most beautiful sight ever seen on the surface of Jupiter. it was verf large, too, measuring 7000 miles across and over 30.000 miles in lengthen 1880 its color . deepened to a brick red. In 1883 it was revolving several seconds more slowly { than when first seen in 1878. A few years later its period was still more j lengthened. In 1880 the spot faded to • a pink color, but had become fainter. It gradually faded "from sight, and ' since then we have heard no more about it. No one has been able.to explain what this spot, actually was. It was agreed that it wag not a part of the planet, and that it w?as not a mere cloud floating in.his atmosphere. While it is an easy matter to tell what it was not, it is an utter impossibility to tell what it was. This w ras the most interesting feature in the history of Jupiter, and tbe mystery which hangs over the nature of the spot does not lessen the interest attaching to it. While the Great Red Spot was at its maximum, so to streak,, a small spot was observed to overtake it, passing round its southern edge. In a single rotation of the planet^ which, as before stated, is less than ten hours, the smaller spot gained 2500 miles on the larger; they passed each other at a speed of nearly 250 miles an hour. A hurricane will travel on the earth's surface at 100 miles an hour. Such a 'furious disturbance levels and destroys everything almost that comes before it. Even a gale which rages at the rate of £0 miles a n hour is quite capable of making conditions rather uncomfortable. Yet the great red spot of Jupiter hag maintained itself against the terrific hurricanes which have been sweeping on to it at the incredible rate of four and five hundred miles an hour. jln the equatorial regions of Jupiter, I where the region of doldrums is, the sun rises to the point overhead every day. The inclination of the orbit of Jupiter to the ecliptic is very small indeed, and is favorabde to the equalisation of day and night Day and night .'.-■<j equal over the surface of the earth twice a yearl— at the times of the vernal and autumnal equinoxes. But over the surface of Jupiter the days and nights are equal almost throughout the year. Nevertheless, they are very short days and nights, being five hours long only in every case. The sun rises from the horizon in the morning and reaches his culminating point in two and a-half hours after he has risen; in tw ro and ahalf hours after he has passed the meridian he is setting in the west. The night passes with equal rapidity. Four large moons are continually illuminating Jupiter, but the light'that all of them distribute on the surface of the planet is far less than our own moon contributes to the earth. The moons of Jupiter shine by reflected sunlight, and they are too far away from the sun to gather a large portion of his rays. (To be continued.)