ASTRONOMICAL NOTES

Press, Volume LXX, Issue 21258, 1 September 1934, Page 7

ASTRONOMICAL NOTES

i ♦ I SEPTEMBER, 1934 i : '3-'r.L']iixT TTi'.m'iN rua urns pusss.j | U'-y L. (~ HOGG, U.A., F.R.A.S.] ! | The sun will enter the zodiacal sign j Libra on September ?A, when the ■ equinox occurs. | The planet Mercury sets on Septem- ! ber 1 at 5.53 p.m., and on September 13 at 7.6 p.m.; its apparent magnitude on the earlier of these dates will be -0.9, on the later it will be —0.3; Venus will rise on September 1 at 5.50 a.m., and on September 15 at 5.37 a.m.: Mars will rise on these dates ■ at 5 a.m. and at 4.32 a.m. respectively. I Jupiter will set on September 1 at I 9.12 p.m., and on September 15 at j 8.31 p.m.; Saturn will rise on these dates at 4.6 p.m. and 3.6 p.m. respeeI lively. | The Sehw assmaim-Wachmami Comet I On November 15, 1927, a comet was i discovered photographically by Professor Schwassmann and Dr. Wach- ; maim at Bergedorf: us subsequent history shows it f.o be one of the most interesting specimens of its kind, which has appeared in recent years, When first seen it had a distinct nucleus and a nearly circular coma some I two months of arc in diameter. The cal- | culauon of its orbit was a rather dimi cult matter owing to its slow motion, j but it was eventually ascertained that its perihelion passage occurred in I July. 1925, and that its period of I revolution round the sun was about , 16.35 years. This comet may be said i to hold several records, as its distance ■ from the sun at perihelion is the largi est known, its eccentricity is less than | that of any comet yet observed, anu 1 it was detected at a longer interval j after passing through perihelion than j any other member of its class. j Still more remarkable than its peculiar orbital conditions are the strange fluctuations which have been observed in its brightness. On November 6. 1929, its apparent magnitude was less than 17: on December 2 it was 13.5, I while three d:-ivs later it had fallen jto 14.5. In February, 1931. when it J was very remote from the sun, there was a striking outburst of luminosity, and its light increased nearly one hundred-fold, and a similar but less marked increase of light occurred in the following December. In February. 1932, its magnitude was 14. with a coma about CO seconds in diameter and a distinct nucleus; in the following December its magnitude had declined to ( 17, but by January. 1933. it had risen : to 12. and the diameter of the coma ; was 40 seconds of arc; it then faded i and had fallen to magnitude 15 by | February 18 and to magnitude 16 by I March 15. Another outburst followed; photographs taken at Bergedorf on I April 22 showed the comet as a bright I circular nebula of magnitude, but a I month later the magnitude was 12.5 i and the coma only 20 seconds in diai meter. I These recurring rapid changes, not : only in the luminosity but also in the diameter of the coma, taken in conI junction with its nearly circular orbit, make one wonder if this strange ob-. I ject may not be after all a peculiar asteroid and not a comet. It passed ' through aphelion last July and is now | returning to its comparative proximity !to the sun. As it has been observed ! every year since its discovery it is , probable that astronomers may be able : to have it under scrutiny during its ; entire revolution about the sun—a fe;u ; which has not as yet been ace ..- , plished in the case of any comet —and , ' by the time its tour of the heavens is ! I completed they may be able to offer i some explanation of the strange fine- - ! tuations in brightness and volume it j has presented since its detection seven. j years ago.

The Yapp Reflecting: Telescope We have had occasion during the last few months to refer to the large reflecting telescopes which are now under construction in the United States, where the munificence of so many wealthy citizens has manifested itself by generous support of astronomical science. It is pleasant to record that the Greenwich observatory is to be enriched by a reflecting telescope of 36-inch aperture, with a dome in which it will be housed, provided by the public-spirited generosity of Mr William Johnston Yapp in appreciation of the personal work at this observatory of Sir Frank Dyson as astronomer royal. There is. of course, no suggestion of rivalling the great reflectors of the American continent. The situation of Greenwich observatory and the climatic conditions are such that a very large telescope could not be used there to its full advantage; such a telescope demands exceptional conditions, and these are not to be found in the outskirts of London. On the other hand there is a growing field of usefulness for a reflector of moderate size yet small enough to be very handy in manipulation, and this the Yapp reflector is intended to be. The telescope is designed for u. c .e hi Cassegrain form; the mirror, silver on glass, is 36 inches clear aperture and 15 feet focal length. The disc is six inches thick and weighs 5501b. Some consideration appears to have been given to the suggestion that the disc should be made of fused quartz, but owing to the uncertainty of success with so large a mirror, the probable delay and finally the unfavourable reports from America on experiments with large fused quartz discs, the idea was dropped. Fused quartz has however, been employed for the Cassegrain convex mirrors, which are of 11 inches and eight inches diameter respectively. The workshop tests of the mirror are good and the images of stars which have been examined in the Cassegrain focus are hard and free j from astigmatism. The dome. 34 feet j in diameter, designed for the Yapp re- j Hector, is built of steel framework j covered with papier mache and; sheathed with copper: its rotation can j be operated by the observer at the! telescope. ! It is intended to employ the Yapp j telescope to continue the work on the ( colour temperature of stars, which for] some years has been carried on at , Greenwich under considerable diffl-' cully with the 30-inch reflector. 7be Presence of Phosphorus in the Sun Solar physicists have had a new, weapon of discovery of great power 1 placed in their hands by the manu-1 l'acture in recent days of camera plates j which enable the infra-red portion of the solar spectrum to be photographed.! and it. is encouraging to learn that on ! the basis of spectographic evidence; phosphorus may now with considerable | assurance be added to the long list of i chemical elements present in the sun. 1 The observations on which this conclusion rents consist of measurements' of recent infra-red solar spectogram.'-, which vhow live faint lines _ having significant correspondence with live which have been obtained in the labor-. atory. '['lie other lines known to exist in the infra-red spectrum of phosphorus are too faint in the solar spectrum to be seen by mean.-' of (he ■instrument used in this investigation. The only other known lines of phos-. phorus. bc.-ides those in the infra-red. lie in that part of the ultra-violet region which is rendered inaccessible to astronomical spectroscopy by the existence in the atmosphere of belts, largely comnosed of ozone, which cut off comnletelv all waves but little shorter than those which give rise to the sensation ot violet light; hence: confirmation ul Un: existence of phosphorus hi f hi,- solnv atmosphere cannot 1 '"■ i:bt:'ir.<:d in tlii.- region of the spec--Ipi' .. Tli ■;!■'!! ! ''i-' o atv vrrv •ii.-iii>- liner in 'iif solar .-•oectriim o-hicl, h.ivf no!

j as yet been identified with those of j known chemical elements, it is prob- . able that most belong to well-known elements but originate under conditions of temperature and pressure j which we cannot reproduce in the I laboratory, and there is little reason ! to think that in the solar atmosphere ! exist elements which do not occur on j the earth or in its atmosphere. Solar Activity and Wireless Transmission Long-distance wireless communicaj tion is brought about by the reflec- ! tion or retraction of electric waves jin passing through the electrified ' regions of the upper atmosphere, now : generally known as the ionospheres, | and in making a wireless journey round the earth the waves are alterj nately reflected by the ionosphere j and the ground. The electrification ,in the upper atmosphere is not by ; any means constant, bein" denser by j day tnan by night and denser in sumi mer than in winter, facts which indi- ; cate quite defntely that the electrifi- ] cation is controlled by the sun. I It is now known that there are two 1 main regions of intense electrification iin the ionosphere—the Heaviside- | Kennelly layer and the Appleton I layer, the former of these is about 100 kilometres above the earth, the latter about 180 kilometres. Long j electric waves are reflected at the i I lower layer, while short waves are | reflected at the higher. The shortest i wave-length that can be reflected de- 1 pends on, among other things, the | density of electrification, hence there • is a lower limit to the wave-lengths ; ! which can be used for long-distance | j communication, and it would appear j that the limiting wave-lemrths whicli i penetrate the ionosphere and do not j return to the earth vary from about ; 10 metres for a summer noon to 23 • | metres for a winter midnight. ! ! The electrification of the ionosphere ; 'is not only subject to diurnal and; ' seasonal variations, but is also proj foundly affected by changes in the , , solar activity, with its accompanying : production of magnetic storms and 1 auroral displays, and two theories have : been advanced to explain the observed phenomena. Birkeland and Stormer, the Norwegian investigators, have 1 suggested that streams of electrified ; : particles are shot with great speed j from the sun and, on reaching the ! earth's atmosphere, give rise to in- j j tense circulating electric currents, to j which the observed effects are due. i The tracks of the charged particles I entering the atmosphere will be in- ( fluenced by the earth's magnetic field and this will intensify the magnetic | and auroral phenomena in the polar j regions. On the other hand, Maris | and Hulbert. rejecting the corpuscu- j lar theory, have, within the last few year*, put forward the hypothesis that ■ all the observed effects may be due ' to the arrival in the upper atmosphere of intense ultra-violet radiation ; emitted from abnormally hot areas . on the solar surface. Time alone will ■ decide as to the relative merits of the two contending theories. Whatever may be the agency by which this abnormal solar activity is conveyed to the earth, the observed . effects are very marked, especially on ' the electric waves of short length. An increased absorption of these waves during their passage through the atmosphere takes place, with the result that communication may be seriously interrupted for days at a time. With, however, more complete knowledge of the relations between the sun and the earth, we may hope that \ the physicist and communications-en- j gineer will be able to effect very considerable improvement."! in the. longrli lrin' Iran-'inis-ion nf rnrliu mi'-.'-