ASTRONOMICAL NOTES FOR MARCH.

Press, Volume LXVIII, Issue 14291, 29 February 1912, Page 6

ASTRONOMICAL NOTES FOR MARCH.

0 . (By the Rev. P. W. Fairclocgh, F.R.A.S.) No spectacular phenomena are predicted for March this year. About three weeks henco the sun will cross the equator, and summer will be at an end. Saturn is an evening star, and is now much further west than Mara, who keeps in the region of Aldebaran, but with a steady loss of brilliancy. Venus is very splendid in the morning sky, where also Jupiter is to bo found, but not so easy as Venus^ Month by month observers report various colours, clouds, spots, and obscurations dn Mars. The large telescope of Meudon showed a great brown spot 400 miles long. This spot has been, seen during several previous oppositions, but never so distinctly as now. The volcanic cloud theory, with special activity at the present time/ is the best explanation. To carry dust 400 miles the atmosphere would need to be less rare than many estimates allow. M. Flammarion claims to recognise several canals besides other objects on ono of Lowell's photographs. In December, Lowell reported that the south polar

snow C ap ] ia d disappeared, but that' other snow spots -were forming outside, as if local snowstorms had taken place around the antarctic circle of the planet. His weather seems to have been like our own. Careful experiments in photographing snow and ice havo yielded results which, when applied to photographs of Mars, suggest that his polar caps exhibit ice rather than snow. Thero is a greenish tint in the caps. Other regions, usually presenting a grey appearance, have been observed to be curiously white of lato. This is the basis of tho cable message that Professor Lowell had discovered frost on Mars. This is not improbable on tho morning sido of the planet. Indeed, many have held tho polar caps to bo little more than heavy frost, for they melt so rapidly in the sun. At the International Solar Research Congress, Professor Hale, of Mount Wilson. California, reported spectral changes in spot spectra which indicate changes in tho strength of tho magnetic field in tho vor+ices of the spots. Ho finds also that the hydrogen lino Ha is more servicablo for investigating eruptive phenomena than tho much stronger Calcium lines. Professor Hale is confident that the relation of the magnetic storm on earth to the solar spot cyclone is being firmly established. All other nations may fairly envy the Americans the splendid equipment provided for solar research by tho Carnegie Institute. They seem never to lack money for a great experiment or a great instrument. Their new 60in reflector proved so effective that it photographed about 30,000 stars in the great cluster in Hercules, where only 6000 had been captured before. No sooner was this success known, than a lOOm instrument was ordered. In England, they would have discussed the matter for many years. English parties are preparing to view the total eclipso of April 17th, 'which will be best observed in Portugal, where, however, the totality will be very brief. Excursions are being arranged to places within the totality area. Tho photographs of the spectrum of Halley's Comet, taken on May 24th, 1910, a few days after we were supposed to pass through its tail, havo been read to indicate that the comet was receding at the rate of 55 km. 34.36 miles per second. Tins is within one kilometre per second of calculated velocity, showing how accurate the spectroscopic method is. Dr.' P. Brock has investigated tht paths of ,102 meteors observed on the .parallax principle, and finds that the average height is just under 80 miles at the beginning of the flight, sinking to 50 miles after a fifty-mile flight. Of tho 102, 72 were Perseids, and their averago height was slightly greater. Tho more rapid the flight the rarer the stratum of air in which a meteor can reveal itself by its friction heat. At such elevations the atmosphere is very tenuous, but when tho velocity of the meteor is known, tho density ot the air in which, it is moving becomes calculable. A unique variable star is known in Andromeda. For about six years it has been steady at tho 11th magnitude. In 1901 it blazed up to the 9th, an increase of more than sixfold. Prior to that it has been observed to oscillate irregularly four or fivefold. Its longcontinued steadiness is very curious. Its spectrum is not that of a variable, but rather that of a Nova, very like Nova Persei 2. No other star is known to have these peculiarities. A minor planet of quite unusual interest was recently captured and lost again. It is known, provisionally, as MT. It was photographed on October 3rd and 4th by Dr. Palish Bad woa- | ther then supervened. It was not till j October 25th that Greenwich got a plate of the region to which the stranger was supposed to have moved. The weather was not first-class, but there was an image on the plate, and it was believed that the wanderer was fairly .gaffed. Next night, however, though the sky was better, no imago could be secured, and henco tho image of the night before was rejected. The peculiarity -of MT. is that its motion between the 3rd and 4th proved it to bo very near the earth. Two positions are not sufficient to determine the orbit, 'but ono somewhat more eccentric than that of Eros would agreo with the positions ob*served. It may bo that thi§ planet is even superior" to Bros- as a means of determining the sun's distance, henco the interest felt in the case. There is probably a large number of asteroids that pass between the Earth and Mars. Three are already known, though Eros is the only one, so far, that is likely to be serviceable. Astronomers will be glad to havo several strings to their bow, for Eros is favourably situated only about onco in a generation. It has been suggested that the object photographed on October 3rd and 4th was. a non-nebulous comet and not a planet. Dr. Crommelin, however, points out that many asteroids are so small and have so feeble a power of gravity that they may bo of any conceivable shape, such as a flat disc, which would bo invisible when edge on. Several planetoids vary greatly in their light. MT. may be a pronounced case of the disappearing trick, and may havo given the imago of October 25th, and havo been edge on a day later. Astronomy has recently been called upon to fix tho date of the original great temple of Amen-Ra, at Karnak, in Egypt, which covers fire times the area of St. Paul's in London. The temple was oriented with reference to the polo star of the period, and the place of sunset on the longest day. The precession of the equinoxes shows that the original building is 5,600 years old. Flainmarion, the French astronomer, thinks that the comets of 1532 and IG6I were ono and the same, and that the period was 129 years. Tuttle's comet of 1862 is related to the Perseid meteors, and has a period of 121$ years. Kiess' comet (b 1911) is_ thought to be the samo as that of 1790, and that this year it made its second return, tho period being about 111 yeare. Now it is well-known that many periodic comets have theiK aphelion near the orbits of the great planets. Halley's, and four or five others, aro associated with Neptune, and have periods varying from 66 to 80 years. A scoro or two are known to bo associated with Jupiter, and have periods of about six years. If it were certain that there are three comets with periods of 129, 121, and HI years, they would fairly suggest a remote planet to whose orbit they make their arctic voyage. Such a planet would be about 48 times as far from the sua as the

earth, Neptune, the remotest, known planet, being only thirty times as far. This inference, even if based on established facts, would not, however, help to find the planet. Tho calculus of probabilities makes it fairly certain that ft comet visiting tho sun from some other star would travel in an easily recognised, hyperbolic orbit. There is, however, no such orbit on record, and it is now doubted whether there are any such orbits. All comets that havo appeared are now being claimed as belonging to the sun. It is true that, somo years ago, one might read in astronomical works of comets visiting us for the first and last time. The prevailing belief that such a thing was'possible influenced this conclusion, but it is now said that thero wero quite insufficient grounds for such statement. So small a portion of a comet's orbit is visible to the astronomer that he cannot predict its return with any confidence, if the period is more than a few centuries. Thero is no reason why there should not ho periods of scores of thousands of years. All such would be beyond tho power of the astronomer to trace, and he, discovering that the period was very great and believing that comets stray from sun to sun, too readily assumed that the orbit was a parabola, or even hyperbola, mid not an eclipse. Xow that the belief has gained a footing that all comets are domestic, they say that all observed orbits aro compatible with the theory that they are immensely long elipses. It may be thought that a period of ( say, 100,000 years would take a comet beyond the sun's control, and into the sphere of other suns. This, however, does scanty justice to tho distance of the stars. Proctor told us yeare ago that it would a comot 8,000,0 v.. years to travel from Alpha Centauri, tho nearest star, to tho sun, supposing it to have just sufficient momentum to cross tho border land, For about, a third of the distance, -and nearly half tho time, it would be under the sun's control. Halley's comet recedes 33 times tho distance of tho earth from tho sun, and takes about 38 years to do it It might go 2000 as far towards the nearest star without trespassing, but such a journey would take three and a half million years, because 6f the constant loss of speed. Our lato visitor has already done about a fifth of its outward voyage. The last tenth will take nearly half its time. Taranaki asks: With reference to the coal found in the polar regions, and also with reference to the glacial epoch, might not the axis of the earth have been changed by tho attraction of some passing astronomical body, just as tho direction of tho pole is now being swayed by the attraction of the sun and the moon on the bilgo of the equator ? The snn and the moon sway the earth because they act continuously for enormous periods of time. Of "their total influence on the earth, the proportion that is devoted to the precesion of the equinoxes, or the swinging of tho pole, is almost infinitely small. . A passing body would act violently for . a short time. It would attract the earth as a whole, pulling it out of its orbit. Tho proportion of its differential action on the bilgo would be quite negligible. Further, a body moving in space, like the earth cannot be jerked into a new pdai* tion and left there. The impulse' once given would result in. a contmuous motion. The pull supposed in the question would Produce a rotation. But the supposed pull is not possible.