ASTRONOMICAL NOTES.

Press, Volume LVI, Issue 16847, 29 May 1920, Page 11

ASTRONOMICAL NOTES.

FOR JUNE.

(sriiCIALI-Y written' i'or. "TUB I'HESS.") (By E. O. IToco., M.A., F-R.A.S.)

The sun enters tho zodiacal sign of ("jnccL* ou #luno wli>jli will |>c the. shortest day of the year in the southern hemisphere. On this day tlio Mm will ri.s3 at 7.36 a.m. and set j nl; 4.27 p.m.. ;md attain a meridian altitude of about 23dcg 2min. Its distance from the earth, will then be about IU.SGO.COO miles. The planet Mercury, which -will bo very far north during the month, will set about the sanii; time as the sun at the helming of the month : on June loth, it "will set at 5.49 p.m. Venus will ho too close to the sun to ho_ Been) during the month. Mars "will rise at 1.23 p.m., and Jupiter and Saturn will set at 9.12 p.m. and 10.S p.m. respectively. During the latter part of the month Mars will ho in clone proximity to Alpha Yirginis (Spioa}-—a star of magnitude 1.2: the brightness of the planet will exceed that of the star by about 1' magnitudes. Although. May 29th, 1919, will bo ohisfIv remembered as the date of tJioi total cclipso of the sun which gave, j the Opportunity of verifying Kinstein's prediction that the sun's gravitation a] field is capable of bending the course of a ray of light, it is also remarkable for somo interesting phenomena, which were seen in connexion with a solar -oromineneo which liad been under observation since tlio preceding llarch 22nd, when it was noticed on the sun's limb extending over some 13deg of solar latitude. On May 27th it appeared as the crest of a high promiuenco coming over tho cast lirnh of the sun with an apparent height of I.smin of arc, and,extending over about 41dog of latitude; on tho 28th it was observed as an enormous body of interlacing streamers having a height of 2.7 mm of arc. The first exposure taken on May 29th showed that the entire form of tho prominence had changed into an arc -l.omins high and extending over •ISdog. of solar latitude. Two hours later it had almost completely severed its connexion with T.he solar disc. The prominence matter continued to move airay from the sun and was family lost j to view when it had reached the enor- j raous distance oi' 17min or .475,000 miles irotu the sun —a. height somewhat! greater than half tho sun's diameter. Few eruptive prominences have been : more completely under, observation than, this one, as during the latter part of its existence photographs woro taken every ton minutes. Apart from tho great height attained, thero is a striking feature in connexion with tho motion which may bo mentioned. ' The upper part of the prominence matter rose from the 100,000 mile level to- the maximum in Glir 40min, or at an average jato of 1-1.(3 miles per second. The motion, however, was as a matter of fncfr far from being as simple as this, j Tho speed of ascent was uniform for a j time, then the prominence matter ap-1 peered to receive an impulse which suddenly increased the speed; after mov-] inior a time at this now speed, an- I other impulse again augmented the speed, and so on. Four well-marked in;pul.ses are disclosed by ;i study of the plates, the first- increasing the speed from 5.5 to 14.7 miles per sec., the last irom 27.9 to 60 miles per sec. The records of tho Yerkes observatory show 14 other eruptive prominences whoso velocities of ascent appear to be governed by the same method of impulses, hut no satisfactory explanation of theso curious phenomena is forthcoming. A stuSj of "tho internal motions of

The first exposure taken on May 29th showed that tho entire form of tho prominence had changed into an arc 4-omins high and extending over 43dog. of solar latitude. Two hours later it had almost completely severed its connexion with T.he solar disc. The prominence matter continued to move airay from the sun and was finally lost to view when it had reached the enormous distance of 17min or .475,000 miles irorn tho sun—a height somewhat greater than half tho sun's diameter.

the prominence shows that tlio up- | ; \ynrd and outward measurements < of t-lic exterior parts woro accompanied by a downward flow ' of prominence matter into a "spot" , associated with it and that tho down-; v--ard speeds increased as the spot ; was approached. 1 . i: M.J.B. writes enquiring as to tlio origin of comets' tails. In reply ■nay be said that when a comet is ob- : served at a great distance from the sun, only • the head and nucleus are usually visible: tho tail develops with close approach to tho sun. Tho nucleus is inall probability composed _of discrete masses of matter which are in continual collision with each other: as a result of these impacts large amounts of ly divided matter would be formed, which -would accompany the nucleus m its journey round the sun. Furthermore, the nucleus —which often occupies an enormous volume of space —would, as it traverses its orbit, gather up to itself all the fine material in space which came within the sphere of its attraction. From these two causes we can picturo the nuclcus as accompanied bv a vast quantity of matter which is only held, to it by tho loose tie of gravitation, j Clerk-Maxwell, half a century ago, from pure theory, and Lebedew and others somo 17 years ago, from experimental evidence admitting of no doubt, | showed that when light-ehcrgy falls on a surface it .presses against that surface: very feebly it is true, but it will cause the body pressed upon to move if i that body is not too massive. _ In this respect light-pressure repulsion and electric, repulsion should act much alike.. These repulsions are effective in prcpOT- j tion to the surface areas of the bodies j acted on, whereas gravitation pulls those bodies with forces proportional to their masses. Now, the smaller a body is the more surface it has in proportion j to its mass: hence the light-pressure repulsion acts more efficiently upon very small particles than upon large ones. A cube of water ono centimetrc on each edge would bo drawn by the sun's gravitational action 10,000 times as strongly as tho pressure of uie sun's I rays falling on it would repel it; but a cube of water only one-thousandth of a millimetre on cach edge would bo ' in equilibrium under the sun's gravitational attraction, and its light-pressure repulsion, and a cube of water with a shorter edge than this would actually uc driven away from the sun. Hence we should- expect particles of matter considerably smailer than tho equilibrium sizo to travel away from the sun with great and . rapidly-increasing speeds. These speeds would bo greater for particles smaller and smaller until a certain limit of sizo with reference to the wave-length oi : light is reached, when tho light would be defracted without transmitting so large a proportion of its repulsion energy to the particles. • . . AVo can scarcely doubt that radiation pressure is an important force —perhaps the only force responsible-for the formation of tho tails of tho comets. The fine material aggregated in and about the nucleus is repelled with a speed which rapidly accelerates, as is well shown by the series of measurements made by Curtis upon points in tho taiL of Hallev's comet. At. a distance ot SOO,OOO miles from the head, the tailparticles were moving with a speed or j about S miles ner second, at a distance | of 2.200,000 miles from the bead their i fpeecl was -27 miles per second', and at j a distance of 8,400,000 milos they were j receding at. the rato of about o 7 miles | por second. . .. . , ! There is ■ another interesting point to bo noticed in connexion with the taus I of comets. These, as is well i point away from the sun, but the popular view that they. point_ exactly . from the sun is seriously in error, as m general they lag behind the lino passing through-the sun and the comets head. It takes timo for the particles repelled from the head to travel out to great distances, and whilst they arc moving out- tho head is moving forward m its orbit. If the sun's repulsive iorce is vastly greater than its attractive iorce, the particles will travel from tlio head with grea*. and increasing speed, and form a tail pointing nearly aw Jl y ironi tho sun. i.e., it will lag behind verj ■ little. If, however, the difference be-, tween the repulsive and attractive. forces is not very great, a. tail will be formed "having a considerable lag. | Hence, if a comet is observed as i» sometimes tho ease—having more than one tail, it is supposed that the tail with the greater lag is composed ot j deusc-r material than that forming the other tail, and attempts have been made to infer from tho lag of the tail th<density of t.ho particles of which it j made up: it must, however, be stated | that no groat trust can bo placed in j tho results arrived at. j . A system of compulsory examination j and treatment of persons aged 40 -would yield a rich harvest in saving lives, declared Dr. Rolle-sion, medical officer ior Peterborough, recently. The death of Mr Sigismnud Kutnou. the originator and proprietor of now's Powder," which, occurred a leu woeks ago, closes tho career of a remarkable man -who built up a big business by advertising, and by energy combined with porseveranco. He staruxi in London about 30 years ago with a small shop in Holborn. Gradually the business outgrew itself and he moved t J i larger premises in Farringdon I where he started advertising on a co r , ~ } prehensive- scale, which resulted in name of "Kutnow" being known tho world over. Mr Kutnow, who was u., was,as unassuming as he was per^cing. Tho idea for his preparation ramo I to him whilo staying at Carlsbad.