AMONG THE PLANETS

Wanganui Chronicle, Volume 90, Issue 24, 30 January 1946, Page 7

AMONG THE PLANETS

SATURN THE MAGNIFICENT NOTHING IN CELESTIAL SPHERE CAN COMPARE WITH IT (By “Tile Sky Pilot’’ of the Wanganui Observatory.) For beauty and interest nothing can compare in the celestial sphere with Saturn. It is unique in the solar system for its encircling rings and 10 satellites. For those who have not seen this lovely object the writer suggests that they take the opportunity while splendid views may be had in the present evening sky, through the telescope.

To the naked eye Saturn appears as a star of the first magnitude, though it may appear dull because ii shines with a yellowish light and without twinkling. At times, however, it will even rival our brightest stars when its beautiful rings are wide open, when it shines with almost twice its usual brilliance. Actually it is excelled in brightness by Mercury, Venus, Mars and Jupiter. At the present time it is situated above and to the ea;t of the ruddy Mars, above Castor and Pollux in the north-eastern sky in the constellation of Gemini, the Twins.

. Through a three-inch to four-inch telescope the system of rings and some of the moons can be seen, but it takes the larger telescopes, such as the one at the Observatory in Wanganui, to bring out the details so much sought after and admired.' In such a telescope it appears as a flattened or bulging globe with three concentric rings about it and several of its 10 moons.

Saturn is the second largest of the planets of the solar system, and for many centuries was considered the most remote member of the sun's family, and the least appreciated, hence its name, because of its dullness and lethargy of movement, an omen of bad luck. Since the discovery of the telescope we have learned that Uranus, Neptune, and Pluto have orbits far beyond that of Saturn’s. The mean distance of the planet from the sun’s centre is about 886,000,000 miles, or about nine and a-half times the distance of the earth from the sun. Sometimes it is further away, and when nearest is about 745,000,000 miles from the earth. Its distance is better appreciated, perhaps, when we say that it is almost twice as far away as Jupiter. For this reason, much less of the sun’s rays and heat reach it, and the long period of 29i of our years is spent in its revolution around the sun. What lengthy seasons this planet has! What long summers and winters!

The planet itself is very similar to Jupiter in that it appears to be surrounded by wide, though less distinct bands of cloud, those at the Equator coppery coloured, whilst those north and south appear greyish with bluishgreen at the poles. And so Saturn lias a dense atmosphere, also suggested from the fact that the edges of the disc are less bright than the centre. These clouds are impregnated with poisons such as ammonia and methane some 16,000 miles thick, covering a depth of some 6000 miles of ice, beneath which is a rocky core ot some 28,000 miles. The spectroscope also reveals a deep atmosphere. These belts of cloud just referred toreally represent clouds of vapour in an atmosphere of great depth, passing one another at great speeds, because of tiie fast rotation of the planet. It is very evident that no life could be expected on such an intensely frigid planet, so cloud-laden. PERIOD OF ROTATION

Sometimes large white spots have been seen prominently on the bands. Sir William Herschel in 1794 observed such and was able to determine the period of rotation of the planet, finding it to be 10 hours 16 minutes, slightly slower than that of Jupiter, making a day for Saturn less than half that of the earth in a vastly longer year. Other men have done the same thing. They discovered that the higher latitudes have a slower rotation. Because of this rapid rotation, Saturn is much flattened at the poles and bulged at the centre, due again to the fact that much of its bulk is cloud. Its diameter through the pole is 68,000 miles, whilst the equatorial diameter is between 74,000 and 75,000 miles. Some other facts about the planet itself are these: The earth overtakes it every 378 days, a little more than our year. It is 734 times as large as our earth, and 98 times as heavy, but as its density is so light (0.7 times that of water), If would float in water if there was a sufficient quantity of it in which to put it. The temperature of Saturn lower than Jupiter. Saturn is travelis —155 degrees C., which is 15 degrees lower than Jupiter. Saturn is travelling around the sun at the rate of six miles per second, or 21,560 miles per hour.. THE RING SYSTEM The ring system is the fascination of Saturn and has thrilled many millions of spectators throughout the world. Prior to the time of Galileo, the system was unknown because the telescope was not in existence. When, however, he looked through his little instrument, he saw what appeared to be three stars joined to one another, or a star with two handles, one on each side. With passing months these disappeared, much to his amazement and horror, but reappeared again to give him stilll greater anxiety. In 1656, however, a Dutch scienti-t, Cbiistian Huygens, with the use ot a larger and better instrument, concluded that Saturn had a ring encircling it. At the time he was afraid io make it known so enclosed the truth in an anagram which, reshuffled inio language, read: “He is surrounded by a thin, flat ring, nowhere touch, ing him, and inclined to be ecliptic."

In 1675 Giovanni Cassini, an Italian, Astronomer Royal of the Paris Observatory, distinguished a division in the ring, thus making two rings, since known as A and B rings, with Cassini’s division, some 3000 miles wide, separating them, and showing A to be some 10,000 miles, and B some 16,000 miles wide. It was fully a century .before the division was recognised as ruch.

The ring system is inclined about 27 to 28 degrees to the ecliptic, and moves along always at the same angles thereby causing the rings to be presented in phases to the observer. Sometimes we are jobserving the full open system, sometimes beneath the rings as at the present, whilst, twice in its orbit around the sun of 291 years, that is, about every 15 years, the earth passes through the plat'e of the rings and the observer therefore sees them edge on,

when they only appear at a thin line across the planet, and not seen in smaller telescopes at all. This Is how they were seen in February, 1937, and how they will appeal in 1951. This is a disappointing phase, but it takes a'ooul a year to move away from it.

• ullieientiy lor us to notice the reopening again. The rings a: e only 111 Io 50 miles thick, and this account' for heir not being seen when they appeal’ edge on. In addition to her rings, Saturn lias l ine moon , though some say 10, of which Mimas is the closest 117,000 miles from the planet. Titan, the largest and sixth out. is 759,000 miles from Saturn. Tills is a little larger Ilian our moon, and Phoebe, the furthest out, 8 000,000 miles distant front ihc planet, whilst the others lie in between. Most o( the moons present

the same face to the planet. Cassini discovered four moons between 1671 and 1684, Tethys, Dione, Rhea and Japetus; Herschel found Mimas and Enceladus with his 40-ihch reflector, and Pickering Phoebe. This latter revolves from east to west, the others revolving from west to east. Such is the grand system of Saturn. What a spectacle it must be for a hypothetical Saturnian, broad brilliant arches of the rings spanning the heavens, and the moons, some small and some large, shining down' upon the planet! Imagine the great shadows of the rings which would obscure sunlight for quite a time! The sun, three rings and 10 moons must indeed be superb from Saturn!

“Seen through the telescope, the golden-hued globe, encircled by its delicate halo of rings and attended by its satellites, stands second to no object in the sky as a thing of sheer beauty.”—Draper and Lockwood. And yet there are many of our citizens who have not seen this lovely sight, though they have in their midst the largest and finest telescope in New Zealand. Saturn will be visible for quite a while yet. See it while you can at your own Observatory.