ASTRONOMICAL NOTES FOR JANUARY.

Press, Volume LXIII, Issue 13000, 31 December 1907, Page 6

ASTRONOMICAL NOTES FOR JANUARY.

■ ♦ . (By the Rev. P. W. Fairi-lough, F.R.A.S.) On January 3rd the moon will pass betwwn the earth and tho Run, causing a total eclipse, which will bo seen on two small islands near Tahiti. Thp totality will be short, which lessens the value of the eclipse. The sun will be close to his nearest point, and so I appear at his largest, and therefore Ikdifficult to cover. Fortunately the moon also is just at her nearest point, being in perigee on the 4th, and therefore, also at her largest. Had the moon been slightly further away the sun would have/appearod as a ring all round her. That would have, been an annular, or ring eclipse. There will Ik> such an eclipse on June 28th, as Been from Mexico. Totality can never exceed. 8 minutes. It is usually about 4 minutes, but on Friday it will bo less. A few years Ihmico "tJiero -will I>e an eclipse with seven minutes' totality. The moon will bo near Venus on the sth, Mars and Saturn on tho Bth, and Jupiter on the 19th.

Six weeks ago when Prof. Pickering announced a condensation in Saturn's

rings, Prof. Salisbury suggested that a now satellite, was being formed out ot tho ring material. Hence, as no passin.ij phenomena demand attention, tho theory of the birth of moons may fairly claim some space, for it is one of the most fascinating efforts of the human intellect, to look into the methods of the Creator.

Tho earth is a hot body getting cooler. It was certainly onco molten, and probably, at an earlier stage, vapour. Every increase of heat would distend the planet's bulk. "Wheu in a state of vapour let us suppose it was •185,000 milos in diameter, or large enough to fill tho orbit of tho moon.

Let us also suppose that it rotated in 12J days. This would make the motion nt the equator about 6000 miles an .hour. If we now supposo the nebula, to shrink to half tho former diameter, tho stuff at tho equator will still go forward at 6000 miles an hour, and, the spin, will only take half ■ tho

time. If we further suppose tho nebula to shrink to the present eize of the earth, with the equator advancing at 6000 miles on -hour, the rotation, would be. flccomplishexi in four fawns. *

This is the first principle to bo learnt. As the heated mass cools and eh rinks tho rotation takes less time/

The next principle is that there is a critical Telocity of rotation at which tho centrifugal tendency, or tendency to fly off, jaifc the equator wonH tonlanco the foroe of gravity. Add the least bit to that critical velocity, and a rupture will ensue. Tho critical rotation in the case of the earth lies between three and four hours.

Is there anything to suggest that tho earth once rotated faster than it docs now? Yes. The tide act* as » brake on the wheel. , Jt js, not the force with which the tide rushee against a continent that W the brake., That is compensated, ac La place argued, by rushee in. opposite directions. There is a friction in the •water itself which 'is believed to be ! slowly wasting the rotational energy. ' Aetronomere have calculated backwards to eclipses of the eun that took place 2000 years ago, and hare found that if tho earth had rotated then exactly am ehe does now, tho totality could not have been seen when it was seen. After making all allowances, it is thought thnt the earth, regarded a* a clock, has lost a quarter of an hour in tho 2000 years, and that would juet put the eclipses right. The day its, therefore, about one eighty-fourth of a second longer than it was 2000 years ago. This is certainly a very small amount, but great mathematicians like Prof. G. Darwin, working backwards into the ages, find thi» «mall quickening of the rotation growing at an ever increasing ratio. At * period not less than 50 .millions of years ago, but probably much more, the earth was spinning six or seven times ac fast as at present.

Let us return to the condensed nebula, tho plastic earth, somewhat larger than now, and rotating in three or four hours. It is very much, flattened at tho poles, and bulged at the equator by the* spin., .Matter at the equator has almost no. weight, the centrifugal tendency is w> great.

At this point we introduce a new factor, tho sun's tide. Thie tide is now as 2to tho moon* 5. But there wae no moon at the tiino we are dealing with, and the oblateness and distention of the heated earth gave the sun more tidal power than ho now has. With a rotation in, Bay, three hours, there would be a tide every Lour and a half j for the eun would raiso a tide in tho viscid body at both eides, juet as at present in the ocean. These tides had a retarding effect on the rotation, and had prevented the critical Telocity from being reached at an earlier stage; otherwise w* might have had several email moon*.

It appears from the researchee of physicists that if the vi&oid earth wero drawn by the eim's tide to the ehapo of a lemon, cay, and if the tidal force wore then suddenly cut off, tiro protuberances would sag back. The lemon would becomo a very flat orange, and then throb back to the lemon shape, and bo on. The period of this pulsation, from the lemon back io the lemon, would be an hour and a half, the same as the interval between the tidee. The throb and the tides, therefore, co-operate. Like the piifih given to a swing, the tides ■pimhed the throb every time in the same direction, till the tide and the throb together rod© poised and hesitating before its leap into space. Then came the tremendous crisis. Ono eighty-first part of the planet's mass eurged too high to return. Like a huge, long drop of viscid matter it still touched the earth, and like a vast waterspout, possibly sucked up more of the weightless matter from thn equator as it came round. We may suppose that almoet at once the "drop" rotated lees swiftly than the earth re-

Jemon-shnped body, earth, and she on W '*-%> pondenco leaves « 0 doubt „ £<Efy\ rauso. Tho earth tide h M her J5& Bnp. •£s/■But tho moon w 240.000 miles Jjjfe how U this accounted iott It JSSc result of tidal friction. The tidal friction Ween t*o force th«n apart. It would diagrams and much space t<. «32&*' tins. Wo must therefor© trust tWD'lifollowers of .\<*wton who assure uiE^ , it » so. It is really an ia.Unoe efSV conservation of energy. «n, e with which the primeval planet is stored up in tho e*rth-moon mS* —oswpt what the sun'e tid« mmS** for. Tho energy with viiich. the «t«U *■< still spins, tho energy of the Moggy" 1 "! slow rotation, and of her orbital ais> '■' tion. together with the energy 2"' would develop by faffing back to tk» , ' earth, aro equivalent to the roUtMßll energy of the rupturing planet tie*. is called "tho ooneerratioo of tbt k». ~ ment of moonentum." Tide-raising power ie invereely v cubo of the distance, not Mffo tavajfcv When tho moon wae at a third ofW*! present distance, she had aet,'«iii-" times but twenty-aeron times hir'|(fc'V;. sent tide-raising power. /m*\^'Tho sun's tide in Venus ii'ab«Lv-> thrco times as great ala ia eartk' ?'■ and in Mercury about nineteen tiimvi. as fjroat. Hence tho eun nag tbfo slow down tho rotation of ifaeMplsiie^u and prevent their rotation from wach-^----ing tho moon casting speed. ka^4 no moons. The earth ahnott atfaaM% having one. The late stage of VitUin accounts for our moon being, in *&££■ portion to its primary, by lar^^fcV" largest moon in the sj-etem. No ift^C, moon is a thousandth part of tbe i^ff of its planet. Ours is one eighty-lfijEb^ Mara being further from the sun^tlp^ tho onrtii , ha* leas aun tide. HelSf-.,' accordingly cast off two moons. Hm% are so email that their tides ia JlSiU 1 were trifling, and they hare not 4&i^ able to move far from him. The wßjisf/< est is only 3700 milat from the(t|^# face of Mara; just outside ReafeiHf , limit. Tho sun's tide has slowed JlJifVl don-n, and this pigmy moon risesi^tfi^ west and fliee round in less t3ia^|^^ hours, while the planet rotate* W'lMi^ hours. Any tide it raises, thtt^bii^'f-" operates in the reverse diroctionifaW'^'.' is slowly_ winding it nearer to* Mrta^ , ,^ Wlien it reaches lloche's limit, 'jt^wflfl^ , be torn to pieces by Mars'e tidal H/mSil^:\ and scattered round him in • riafr^l Our own moon, by «et^« supposed to have been a coharait maw f $ but a whirling swarm of particles,.tiK it go* beyond 2.4 radii of the ea^i'-^ away from the centre. - „'. #£ ,g; Jupiter and all the outer planets *rf4r for little friction from the sun's tljlai^.' and they have numerous moons. !t&j& deed, moon casting' was one ithiwfi method«'liy:?nliieli, the aoceleraitaa,;^ their rotation" was checked. They emo?, a moon, possibly in a ring,, from *h*irt| equator,, and tb.en - the, mdrfsiqiflf' moving matter from hitjher UUtmota,^ flowed into the breach. i!Mb '.'matt'efjl. had to bo accelerated, and that "••ftS? up a little energy, and slowed the rolall tion down. In process of time furt|i|i ; shrinking brought op the speed,, aji&r, another crisis enstied. ■ Hence SatomM 1 I nine or ten moons and hie rings. f^iil A volume is required to duKjaap^jlH^; the (details of this remarkable thif^M of the genesia of noons. Kotma^ffp .more than the most condensed U*s|fiMl ment has been possible here. ' Kiß*||fcS han been said, however, \ to" ajhrifejiS. bird's-eye view of one of the moet"ofce||' acteristio diaptors of modern imm/Mt, ing and speculation. Almost tifttf "&§&'[ jeotion tliat can'be suggested, is ceptiblo of such an explanation as l^»t|)s lend further probability to the dafia||% hypothesis. f :)\ '^jM Mr Nikola Tesla, m^ Christmas D*y t IJ mado an announcement more euitabW^' to the Ist of April. .' Aid*d , byj*^| Niagara Companira he isigoia^to d&vjjg patch an eight hundred aiilbCM. Iwrse^ power wireless message to" Man.\- *A|^ ( the total power of tb» falk UrmtT^ one-fiftieth of the abore, and,ai^Mt||| ono-twentieth of that power" \i» t y4|'M; utilised, we will hold the tofio^evaV^ Some years ago an old lady l*ftf';M|| fortune to promote sienalling to MeWfli Perhaps Mr Tesla ha* got hold legacy. In any case, he wlU'ienmJ||| splendid advertisement. ;•' ,