IN STARRY SKIES

Evening Post, Volume CXVIII, Issue 23, 27 July 1934, Page 18

IN STARRY SKIES

THE SUN'S FAMILY

(By '' Omega Centauri.'')

'in very early times it must have been Recognised by primitive man that the earthy"the sun, and the moon are in,-some/way related to oho another. The-: character-of .tho relationship was very naturally -misunderstood. The sun and the moon appeared to bo attendants or of tho earth. The sun evidently did splendid work in supplying the arth with warmth and light The,.moon did not appear nearly so efficient. It- hud no appreciable effect on the temperature and, even as a light-giver, it was more or less erratic, being often a,bovo the horizon in the. day; time, when its services were not required, arid failing to relieve tire long hours"o£ darkness. It required nvueh keener observation to ■ separate the planets, or wanderers, from the rest of the starry hosts, and after this had been done it took some thousands of years to interpret their complicated motions.; The solution of the problem led to the dethronement of the earth from its'proud position. Not only the;earth and moon but all the wanderers' as well, were found to be j children or. attendants, of the sun, and as a further shock to tho pride of man, i the earth .was found to be one of the | little one's.7 ' "We cannot get far in as-j

tronomy : without, coming across very largo numbers, the full significance of which it is hard to realise. Millions, I billionsj and trillions sound much alike, j tot according, to, the English usago a jKHiop isa /million million, and a trillion, .iai. ay million:.billion. As a first step .we should try to picture to ourseyes . the • meaning of a million. If! wo went twice to the moon and back, or: if :we travelled forty times round the world, we should not have gone a millioa miles. Thales, of Miletus, is said to have predicted an eclipse of the sun,. which, put an end to the war between the Medes and Lydians. This eclipse-is believed, to have taken place on September 10, 610, B.C. We shall have to wait nearly two more centuries before: a million days will have elapsed BJti.ce :that memorable .date. Now, even in stating the distances apart of the members of the solar system, wo shall have to speak not only of millions "but of thousands of millions of miles. Astronomical distances are inconceivable, but it is so important to form some conception, however inadequate, of the grandeur and immensity of the uni-! verso, that it is worth while making an attempt to create .sonic sort of mental scale. We must start from the earth | and proceed gradually from the known j towards the unknown. , Our first study then should be the structure, the dimensionsj and the motions of the solar sys- ] tern. . The initial difficulty is to > picture its emptiness in relation to its size. The clearest way is to mako somo kind of model, real or imaginary. But we are faced at once with a dilemma. If wo make our model moderate, in size the separate bodies will be too small to be visible. If on the other hand we make all a fair sizo and true to scale most of them will disappear in the distance. An ordinary orrery; yith balls to represent the planets, all mounted on wire arms to enable them, to revolve; is most misleading. The scale is- altogether wrong. It is hopeless to attempt to make a true working; model which will fit into any building. '. It. is - better to make spheres which represent tho planets of Teasonable sizo and leave the actual working of .the system to the imagination. A most convenient scale is that in which a million miles is represented, by a yard. A globo 31 inches in diameter then stands for the sun. When the. models of tho planets and their satellites are constructed to match this, it will be found that the whole lot will fit easily, with plenty of room to spare, into an ordinary chalk box, 6 inches by 4, by 3. Tho total volume of them all.is only about one six hundredth part of that of tho sun. If we, are to allow these tiny spheres to move at their true relative distances •n-e shall need a space 4} miles across in. every direction. For the four inner planets wo may take two beads and two. peas. For Mercury we need a bead one-tenth of an inch in diameter, nncl fot Mars one half as large.again.

For Venus and the earth we can choose a couple of peas each slightly more than a quarter of an inch in diameter. Tho more exact values for the last two | are .273 and .285 of, an inch. For Jupiter, the giant of tho family of planots, and for Saturn; the great ringed globo, wo may use a cricket ; ball and a tennis ball respectively. ' Strictly each should bo rather larger, ' the model of Jupiter being 3 1-8 inches i in diameter, and that of Saturn 2.b" . inches. The. rings of the latter can i bo cut from thin paper 6J inches across. For Uranus' arid Neptune wo can use 1 marbles 1.11 and 1.18 inches in dia- • meter, and for Pluto a very much i smaller one. . To complete tho set we l shall now require a number of tiny . beads and a- multitude of grains of ■ sand to represent the asteroids and the i satellites of the planets. The model ; of tho moon, for. instance, will be only • one-thirteenth of an inch in . Two of the satellites of Jupiter are about twice the size. Two others, as . well, as Titan, tho largest satellite of . Saturn,; and probably the satellite of i Neptuno are much the same size as our ! moon. The largest of the other satellites and asteroids have diameters only about half that of the moon and tho majority; of both. classes of bodies are ever so :much smaller. - Now let us imagine all these tiny models sot moving: with appropriate speeds in.orbits.of true relative sizes ■ in; a. great field. ■ Since the orbital planes aro; all inclined to. the/ ecliptic, the ;field cannot be level; it'must, in fact, be. mountainous. , Moreover, even if the field was devoid of grass or

anything to hide the models, they would nearly all be invisible or- extremely difficult to find. That of the sun would bo the,only one seen from a distance It must be placed, in-tho centre, and an elliptic .path,--not differing greatly in most ..eases -from, a circlo, must be smoothed out for' the orbit of each, other body. We have got into the way of according the earth' special privileges, so we shall make tho piano of its orbit perfectly level. All the other orbits will then be more or less inclined to this ecliptic plane. - The surface of the field will therefore bo undulating or hilly, and in one belt mountainous. Each orbit rises in one partabove tho ecliptic and falls below it in the opposite direction. The highest points reached by tho various bodies aro in very different directions from tho sun. The heights and depths attained also vary very widely. Tho orbit of Mercury in our model rises only about 13 feet.above tho ecliptic and falls a similar amount- below it. Venus does much the same in a different direction. Mars, Jupiter, Saturn, TXranas, and Neptuno rise and fall about 21, 33, 116,. 72, and 260 feet, respectively.-. If these were all, onr field might not be too.rough for golf links.- But the asteroids present a difficulty, their orbits being interlaced and at widely different slopes. It will be impossible, to represent them all on any_ single surface. But that the region between the orbits of Mars and Jupiter will have to be very uneven may be,seen from,the fact that the model of Eros will have to rise only 75 feet, whilst that of Hidalgo will roach 1086 feet above the ecliptic. To find any particular bead or grain of sand in such' a paddock will be much more difficult than to locate tho proverbial needle in a haystack. The orbits, we must remember, are spaced out widely. Tho mean distances of tho models of the planets from that of the sun will be Mercury 36, Venus 67, the earth 93, Mars 141.5. Jupiter 483, Saturn 886, Uranus 1783, Neptune 2793. and J>lnto 3700 yards. If they all revolve with appropriate speeds tho bead that stands for Mercury will com-: plcte one revolution in 88 days, and j tho peas that stand for Venus and the j earth will take 225 days and ono year respectively. The tiny -bead that j stands for-the.moon must circle round! the pea-sized earth at a distance of; 8} inches, about thirteen times in a i year. The models of Jupiter, Saturn. Uranus, Neptune, and Pluto are much more leisurely in their movements, taking 12. 29, 84, 165. and 248 years respectively to complete a single revolu-tion.--Wre-must remember that'speeds as well as distances have been reduced 1760 million times. This model of the systom should help us to- realise the emptiness- of space even -within the sun's family. But this emptiness is nothing to what we shall find whenj we visit more distant parts or' the j universe. --■ . ... - ...