ASTRONOMICAL NOTES.

Press, Volume LIX, Issue 17750, 30 April 1923, Page 5

ASTRONOMICAL NOTES.

F.OR MAY. (SPICIALLr WRITTEN TOR "the pbess.") Bt E. G. Hogg, M.A., F.R.A.S. The planet Mercury sets on May Ist at V 5.43 p.m. and on May 15th at 6.28 p.m.; its apparent magnitude on the earlier of these dates is 0.1, but by the later date it will have fallen to 1.7. MeTcury will bo in inferior conjunction with the sun on May 29th, and will be invisible for some time after that day. Venus rises on May Ist at 3.54 a.m. and on May 15th at 4.23 a.m.; Mars sets on these dates at 6.27 p.m. and 6.0 p.m. respectively. Jupiter rises on May Ist at 5.15 p.m. and on May 15th at 4.5 p.m.; Saturn rises on these dates at 4.11 p.m. and 3.14 p.m. respectively. Buring the month the moon will occult the planets Uranus, Venus, and Saturn. The earth nnd moon will bo in a lino with Uranus on May 10th ftt 6.47 p.m., with Venus on May 13th at O.G p.m., and with Saturn on May 27th at 1.56 a.m.

At the first meeting of the International Astronomical Union, wbich was hold in Rome in May last, tho commission appointed to consider the question of calendar reform recommended that the year should'consist of 52 weeks with one and (in leap-year) two days which should be regarded as outside both the week and the month —ns described in these notes for September, 1921 —that the lengths of the months in each quarter should be 30, 30, and 31 days, and that tlie year should begin at the winter solstice. These changes would undoubtedly lead to a great improvement in tho civil calendar, and it is greatly to be regretted that the Union could not see its way to taking the necessary steps to bring the subject vigorously before the Legislatures of the several countries represented at the meeting. _ A Bill has, however, been introduced into tho United States-Congress authorising and requesting the President to call an international conference on the subject this year, and we may hope that some progress will now be m»ido in educating public opinion on tho matter. In the meantime, two new schemes for improving the calendar have been put forward for our consideration —and, as each possesses novel features of its own, a brief description may not be unwelcome. The first is advocated by Mr Charles P. Marion, of the U.S. Weather Bureau, who urges the adoption of a 13-month calendar, each month consisting of four weeks exactly. One day in tho year, preferably the last, would be outsido week and mouth, while in leapyear there would be another such day, which might conveniently precede the first day of the seventh mouth. There is much to be said in favour •of any schemo liko this which equalises the months and greatly simplifies the comparison of all monthly return* and records. In addition, since each particular'week would then always occupy the same place in the solar year, monthly records oould he supplemented by, weekly ones. Monthly payments would be made 13 times a year instead of 12, and the anomaly of paying the same amount for 31 days as for 28 would be gone. Mr Marion's proposal removes ono of the chief objection* to our present system from the astronomical point of view—the occurrence of the leap-year <£rly in the year. This flaw is not due -nj-Julius Crosar, for he made March the first month, as the prefixes Septem-, Octo-, etc.,' still remind us: he saw the advantage of placing the leap-day at the end of the year. The second' plan for reforming the calendar is due to the Rev. D. 11. Fotheringham, one of the greatest living authorities, on astronomical chronology. He suggests that tho ordinary year should contain exactly 52 weeks or 364 days; it could be divided l into four quarters, in each of which the lengths of th'e months would be 30, 30, and 31 days, or, if preferred, there could be-13 months of four weeks each. To account for the missing days every fifth year would have an extra week, unless the year was, divisible by 45, in which ease there would be no extra weak; there would thus bo eight extra weeks in 45 years: The error introduced 1 into the oalendar by this method would be one day in- 440 years, and this could be* corrected by dropping the extra week once in 3COO years, in addition to its normal omission every forty-fifth year. - Assuming that the extra/ week is always reckoned at the end of the year, Mr Fotheringham's proposal would secure the following desiderata: (1) Any particular calendar date would always be on the same day of the week; (2) v the interval in days between two dates in different years would always be tne same. The fact of the sequence of week-days going on unchanged would be likely to remove opposition from ecclesiastical and other quarters, but the unequal lengths of the years constitute a serious objection and it is. not probable that any strong body of support would be found for a scheme so artificial in its structure. Messrs Marion and Fotheringham are, however ; doing good work if, by the publication of their projected reforms they draw attention to the need there is for some improvement in our calendar.

The stars nearest the earth are at such stupendous distances that though thev are :often moving with great velocities it is only aftec the lapse of long periods of time that any apparent changes are wrought either in their positions relative to the adjoining stars or in their apparent brightness. Mr 0. L. Stearns has recently investigated the changes in the aspect of the skies produced by the motion of some thirtyeight stars, which are known to 'fce within twenty-two light years of the earth, and from his paper we select a few of his conclusions which may be of interest. We find that Alpha Centauri —the brighter of the two pointers of the Southern Cross —is moving across the sky at the rate of 3.68 seconds of arc per annum, and also away from the eartn in the lino of sigh* at the rate of 14 miles per second. Combining these two velocities Mr Stearn& finds that Alpha Centauii was nearest to the earth about 28,000 years ago, - when its apparent brightness wae equal 0.5 instead of 0.2 as at present. Sirius on the other hand is moving so that it is gradually approaching the earth, but so slowly that it will not he at its minimum distance from tis for 6.5,000 years and then its apparent brightness "will be only one-fifth of a magnitude greater than at present. Altair, the brightest 6tar in the constellation Aquila —will suffer greater change than any other star given in the list, for after the lapse of 117,000 years its distance from us will be considerably less than half of its present value and its apparent brightness will be so increased that i* will then shine almost as '.brilliantly as Canopus- does at present. Barnard ; s star —sometimes referred to as Gilpin—which has a motion across the sky of about 10.333 seconds of arc per annum and a velocity of approach of about 50 miles per second will in 6ome 10.000 years be nearly as ciose to us as Alpha Centauri is, but it is of such feeble luminosity that it will not even then be visible to the naked eye. Generally speakinp- we mav sav that if we could revisit the earth, after the lapse of manv thousand years the changes yce should notice in the appearance of the heavens would be extremely slight. From Harvard eomeß intelligence or a new record in stellar velocities, in

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the constellation Copheus is a saiht star —E.Z. 223564 —a cluster variable of tfie- usual Cepheid type, in which the interval of time between two successive maxima of brightness is only about 6 hours. The study of this class of variable i star has led to the discovery of a law connecting the period of variation and the intrinsic brightness of the star, so that when the period and apparent brightness are known, it is possible to estimate the distance of the star from the solar system; it is inferred that the star under consideration is about 3SOO light-years away, i.e., it is nearly a thousand times further from u's than is Alpho Centauri. It has also been observed that the star is moving across the sky at right-angles to the line of sight at the rate of about one-fifth of a second of arc per annum. Combining this last result with the inferred distance, it follows that the transverse velocity of the 'star is no less than 700 miles a second, a speed much greater than any hitherto founct for a star, and comparable with that found by Slipher for certain spiral nebulas. Our star is probably >too faint to admit of a measurement being made of its velocity in the line of sight, so that the actual speed with which it is moving cannot yet be stated. What we do know, however, about its rate of motion is sufficient to enable it to be regarded for the present as holding the record for stellar velocities.

All stars are in motion, but, so far as our present information goes, the average speed with which they travel does not greatly exceed that of our sun, vis., about 12$ miles a second. As each star is subject to the gravitational influence of the remaining stars of our un'verse, its velocity must, iu course of time, vary. One approaching the main body of the Milky Way 'must movo with a gradually accelerating speed until it has penetrated deeply amid the countless stars 'existing there, when its velocity will be slowly diminished. If it plunges through without any catastrophic encounters, and starts to leave the galaxy, the combined pull of the stars it is retreating* from will slowly tell, and after perhaps millions of years have elapsed may bring it to rest Wo picture it as then retracing its .path, gradually acquiring speed as it again Lars the galaxy, passing through it once more, and so, during an almost endless time, performing oscillations of a trulv stupendous nature. Astronomers, however,, contemplate the occurrence of eases m which, by ome fortuitous relations ot coniparaJiT proximity to other gravitating F „ ..,rmiv aequirea velocity so "Tthe combined Attraction of all the othe aHs Capable of holding it wk Into the outer space it passes «,. a lonely flight to which we can picou a loneiy g Possiblv the star, in STstwLh we have referred i, ililTa to pursue this course :L the Jhances of an encounter which 'would "modify its speed or direction as.to bring it back to our um/erse are Snail for it has been-computed that Tatar is likely to. nyeet with' such a near approach of another, star as w-ould nroduce this result only once in about a hundred million-million years. To many stars the appellation "runaway" has been given, but none has apparently so gojd a claim to the title as this record-breaker.