ASTRONOMICAL NOTES.

Press, Volume LVIII, Issue 17419, 1 April 1922, Page 15

ASTRONOMICAL NOTES.

FOR APRIL , tL j written job "the priss . ) (SPf ($t E. *»• Hogo, M.A., F.R.A.S.) a n i a net Mercury rises on April Ist % a m., and on April loth at 0.40 al between these dates its apparent will change from -0.1 to " H hence during tho first half of tho 1 - t 6 hould he a conspicuous object Ise to tho sun to be seen with the i eve Venus sets on April Ist "nd April'lsth at 6.30 p.m. and 6.6 a ° respectively. Mors rises on these Ss at 8.58 P.m. and 8.17 p.m. re--pHvelv' its magnitude increases dur- £.»»» - 0J T O .'V" 0 " •? «-ill rival Canopus in brightness, hmitcr rises on April Ist at 6.1 p.m. '■nd on April 15th at 5.1 p.m.; Saturn ;^ s on these dates at 5.43 p.m. and 14G pm. respectively. The Planet Jupiter will be in aphelion »J£ii sth at 7.30 a.m., when its ° n +aJrlfrom the eun will bo about ««000 miles. Jupiter will bo occ l ifflTtto moon on 1 April 11th the 7™ nf the moon and the planet be- ' • n-i line with the earth at 8.1 p.m. °, f r ultati T h S imwever, visible only in places, south ot Idtudo 'tCdog South; at Chnstchurch fi iUshou- as a close graze, the planet naming exceedingly near to Hhe moon s & and should be an interesting specK to watch. . The moon rises on the 'Sin" question at 5.9 p.m. We bam from "Popular Astronomy ♦hit sixPossi b] byy «° V€n ' T'enod'c comets ' uYs perihelion this year. Of ' ! r orsen's short-period comet ha 3 e n kt & 1879, and Barnard's 1884 if hL not been seen at any of its r&®nce 1884 henee there is Lne of either of these being de- ' Sd while the elements of Metcdf 8 1 1906 VI. are so nncortain that it S be unwise to count on seeing it Sfvear. Taylor's comet 1916 1. is £ a t perihelion about tho middle, of Tkne but it wiU not bo well placed for observation. Daniel's comet 1909 TV is due about the end of September; i-hen it passes through its perihelion position it will be about 80 donees from the sun. Pemne's comet 1898 VIII is due at perihelion about October Ist, but it will not bo pl&oed for South.era observers. Do Vico's and Brorsen 9 long-period comets, each of which takes about 75 years to complete its orbit round the ' sun, have had their return predicted ftrr 1922, but the periods of both are uncertain by several years, and so no forecast its to when we may hops tc seei them can bo mndo with any approach to accuracy. If detected they will be found accidentally or incidentally m tho course of othor work than the searon f#r them. Comet-seeking is work for irnch small telescopes are mast suitable; it is encouraging to the amateur wknow that the instrument with which Jfjjdsior, who is credited with discoverlrig 14 comets, used to sweep tho h#ivena was a telescope of only two S inphea aperture. Pons, however, 'holds apparently the record, as he detected nfr fesa than 29 comets, but the present writer is unaware of tho siee of the tdescope employed by (him. Jlie comets of do Vico and Brorsen, lilw that of Halley, belong to what i 3 called tho Neptune family, as the outer parts of their orbits—the aphelia—are itt the vicinity of Neptune's orbit. There are six comets in this group, with periods ranging from 60 to 81 years, and it would be a curious coincidence if : two of them should come to perihelion in 1922. Unlike the short-period comets, they are for the most part striking Epectacuiar objects, and give ; a far better opportunity for studying the structure and composition of these • celestial bodies than do the telescopic ones which ate so frequently in evidence.

' 'Our knowledge of the material out oE which comets are made is still someFrom the behaviour of weir' tiils, Bredichin concluded that lydrpgWiSP the hydrocarbons and iron wsft'foongst. the substance composing WOsts, but Professor W. W. CampWl. writing recently states: "UnfortuMWjt it is far from certain that hywßgeaiwistfl in comets, and iron has jW: reported for only on© comet." 3£We is_a great variety of comet spec- ■ . w> indicating as great a variety of , ifopetery contents or conditions. In oases the spectrum seems almost ■ ?r , 'v .continuous, while in others . - Ipght lines or bands are visible. Other , are a combination of'continuWtaad bright-line light. The spectrum pktjte nucleus seems to be always conTjliaoiiß, or continuous except for Wtorption lines, and in these latter Ws it is fairly certain that the is shining by reflected gunIn some cases it may, however, Wftm that some other form of luminescence capable of yielding a continuous iPjjjjtrum is present. *he heads of comets and the parts W the tails near the heads generally Wow a spectrum of bright bands, which ' k , 80^ ela l decades were hydrocarbon Dttds, but more recent observations . Sjj 6 wade it probable that this speowl)m does not indicate a combination '{hydrogen and carbon, but that it is - ? r ono the low-pressure carbon ICSti or ' results from one of I jSjt C(> ™Poundß of carbon and oxygen, from carbon monoxide. The fejlgw and bands of cyanogen—a nitros', jea compound —and of carbon are prejjf without any question in the heads iy mner tails of many comets, and ' .has recently identified carbon - spectra of the tails |!Mha comets of Daniel (1907) and " 8e (J-908). The presence of ? -WKam jn the cometarv nuclei also 1 « 8 There are, : er ' ma . n y points in the stracture ] 5* tt composition of comets on which ' v ita * more light, and doubtless when ™o expected long-period comets their appearance, yet more of r'fc 8 6ecre^s will be wrested from j ast meeting of the American * ,2? ronolnica l Society, an interesting 3 *BB read by Father Luis "A Probable Influence r" the Earth_qn the Formation of SunL jffih * n which he gives certain conloa3. he has arrived at from the P'3ooo negatives of the sun taken the period 1010-1920 at the del Ebro, Tortosa. of has recently been appointed 9 ur au thor finds that more Kffir been formed on the invisible P®» iik 8ll j Lan on . the one facing liMißiki 811 a t result is par-. marked in the case of very j 101 Buch spots during the eleven yearp by the observations, only nine Im&l.tP™ mthin 70 degrees on either cen tral meridian, which is ||gK?® Man one-third less than would ["V* casual distribution. He iu a the number of spots .eoflt Bide of the central 38 25 pear cent, greater iffifgfjfff bom on the west Bide 7ft T 1 ® origin■liwttliin degrees of the central omy one can be ascribed with >g the west region J -Kedea then examined his ® ao any jelation existed the position of IStW'JObn « wbit, and found that Kwfflu e w V spots during Jun0 j July—- , 18 farthest from - y per cent, the BmW™ l "?' ,dTirm tr November, 3>eI^Wa^mSS;^.'? annar y» when the earth ag ?* ?°d that tha very the aphelion ®°rethaa 10 per cent, in

excess of those born during the perihelion months. It may be added that the results obtained by him as to the mean areas affected by spots agree closely -with, those reached by slrs Maunder for the period 1880-1901. In previous "Astronomical Notes" attention has been drawn to some of the important*work bearing on this subject, which has been published during recent years. Of great value was Mr E._ W. Maunder'a paper in which he pointed out that the number of faculw observed on the eastern edge of the sun at Greenwich during the period 1886-1916 was 3 per cent, greater than the number seen on the western and not less interesting and suggestive was the announcement by Mr Evershod in 1919 that ho had found that tho light Miming directly to the earth trom the solar hemisphere nearest to ua differed apparently _ in its spectral effects from that which reaches us from the further solar hemisphere after reflection from "Venus, when near superlor conjunction. The conclusions reached by theso astronomers certainly lead support to the view held by Father Ilodes that the earth exerts an influence on the sun which modifies the distribution c f sun-spots and other surface phenomena.

"Why our eath," writes Father liOdes, 'should have this influence it is difficult to say. Possibly it could be explained by assuming that this effcot is not a function 0 f mass and distance alone, but of some other property say, magnetism or electricity, which our planet might possess in a high degree, aa it possesses the greatest density of our system" The suggestion here made is too vague to carry u ;S far; in a large sun-spot we have an intense magnetic field, and it is highly probable, if not certain, that the magnetic storms which occasionally visit the earth have their origin in sun-spots, but as yet we have no evidence whatever that such mag-nf-tv-, or _electrical properties aa the earth or its atmosphere possesses have any causal connexion with the birth and development of a sun-spot.