ASTRONOMICAL NOTES.

Press, Volume LXVIII, Issue 20612, 30 July 1932, Page 6

ASTRONOMICAL NOTES.

AUGUST, 1932. (SPBCtALLI WRITTEN FOB THE PRESS.) CBY E. G. HOGG, M.A., F.U.A.S.] The planet Mercury setß cm August Ist at 7 p.m.; it will be in inferior conjunction "with the sun on August 17th, and later on in the mouth will become visible in the eastern sl\}. Yenus rises on August Ist at 4.37 a.m. and on .August 15th at 4.20 a.m.; Mars rises on these dates at, 4.50 a.ui. and 4.37 a.m. respectively. Jupiter seta on August Ist at 6.31 p.m. and on August 15th at. 5.51 p.m. and Saturn rises on these dates at 4.8 p.m. and 3.8 p.m. respectively. Venus, which has presented of late such a beautiful spectacle in the eastern sky, will attain its maximum brightness on August sth, when its apparent magnitude will be 4.2. The motion of Jupiter relative to the bright star, Regulus, will be interesting to watch during the early part of August; the planet's motion will carry it very close to Regulus, their nearest approach being on August 11th, when they will differ by less than five minutes of arc in right ascension and ono minute in declination. August Stars. The following bright stars will cross the meridian of Christcliurcli on August Ist, at the times and altitudes above the horizon given after each star; the number in parentheses following each star is its apparent magnitudo as listed in the Nautical Almanac. If the times of meridian passages are required for other days of tho month it will be necessary to subtract Smiu s(ssec for each succeeding day. Towards the north wc have Epsilon Scorpii (2.36) 8.5 p.m.; alt. 80deg 38min; Eta Ophiuchi (2.63), 8.25 p.m.; alt. 62deg 7min; Alpha Herculis (Var.), 8.31 p.m.; alt. S2deg.; Nu Scorpii (2.80), 8.45 p.m.; alt. 83deg 43min; Lambda Scorpii (1-71), 8.48 p.m.; alt. 83deg 41min; Alpha Ophiuchi (2.14), 8.51 p.m.; alt. 23deg 52min; Theta Scorpii (2.04), 8.51 p.m.; alt. 89deg Somin; Beta Ophiuchi (2.94), 8.59 p.m.; alt. 41deg 52min; Gamma Sagittarii (3.07), 9.20 p.m.; alt. 76deg 54min; Delta Sagittarii (2.84), 9.36 p.m.; alt. 76deg 20min; Epsilon Sagittarii (1.95), 9.39 p.m.; alt. 80deg 53min; Alpha Lyrae (Vega) (0.14), 9.54 p.m.; alt. 7deg 45min. Towards the south we have Alpha Triang. Aust (1.88), 8 p.m.; alt. 64deg 38min; Zeta Arae (3.06), 8.12 p.m.; alt. 77deg 39min; Beta Arae (2.80), 8.39 p.m.; alt. 78deg 4min; Alpha Arae (2.97), 8.46 p.m.; alt. 83deg 43min; Beta Doradus (3.81), 8.52 p.m.; alt. 16 deg 4min; Eta Pavonis (3.58), 8.58 p.m.; alt. 68deg 50min; Alpha Argus (Canopus) (—0.86), 9.41 p.m.; alt. 6dcg llmin. . ,

Of tho above stars we may note that Eta Ophiuchi is double, tho two components having magnitudes 3.2 and 3.7 respectively. Alpha Herculis also double; the brighter member is variable, its apparent magnitude ranging from 3.1 to 3.9, while tho fainter is of magnitudo 5.39, tho two being 4.7 seconds of arc apart. Vega is tho brightest star in t"he nOrthorn hemisphere and is of interest as marking roughly tlic direction towards which the solar system, with its attendant comets and meteor trains, is moving with a speed of about 12} miles a second

The Beinmuth Object. In these notes fot last mouth a brief account was given of an asteroid —tbo Dolporte object—whose orbit was such that it approached -within ten million milos of the earth or two-thirds of the distance -which separates us from Eros when tho latter is nearest tho earth. Wo have now to chronicle the discovery of a body—the Eeinmuth object—whose, motions are more remarkable even than tliOße of the Delporto object. On Docember 31st last Ilerr K. Keinmuth, in the course of the regular work on minor planets carried on at the Konigstuhl Observatory, Heidelberg, detected an object, of magnitude 15, whose aspect is described as being decidedly nebulous on four different photographic plates; it was therefore inferred to bo cometary in nature, though its movements were very similar to those of an ordinary minor planet. Great difliculty was found in fitting the observations into a parabolic orbit but an elliptic orbit calculated by Dr. Strack agrees well with them. According to this computation an asteroid of surpassing interest has been added to the long list of such bQdies, as Dr. Strack finds that it performs its journey round the sun in the very brief period of one and two-third years, that its perihelion is within the orbit of Venus, and that it passes within three million miles of the earth at two different points in its orbit. Its aspoct is now declared to be stellar. It was observed by Professor Bianchi, of tho Milan Observatory, on May 12th, when its distance from the earth, according to computation, was C.7 million miles; this is likely to hold the record for some time as the least distance from the earth at which a planetary body has ever been seen. Much work, liowovor, has to bp done before the orbit of the body can bo considered as definitely settled. ! The Observation of Stars. In his "Outlines of Astronomy," Sir John IJerschel makes a statement relative to the observation of stars, which is of interest to all who watch the heavens at all closely. Writing of the striking cluster known as the Pleiades, he remarks "six or seven stars may be noticed if the eye lbe directed full upon it, and many more if the eye be turned carelessly aside, while the attention is kept directed upon the group." To this he appends the following note: "It is a very remarkable fact, that the centre of the visual area (of the eye) is far less sensible to feeble impressions of light than the exterior portions of the retina. Few persons are aware of the extent to which this comparative insensibility extends, previous to trial. To estimate it, let the reader look alternately full at a star bf the fifth magnitude, and beside it; or choose two, equally bright, and about 3 or 4 degrees apart, and look full at one of them, the probability is, he will see only the other. Tho fact accounts for the multitude of stars with which we are impressed by a general view of the

heavens, their paucity when we come to count them." In this connexion we may quote the following passage from Webb's "Celestial Objects for Common Telescopes"— a mine of information for the amateur astronomer. In dealing with the mode of observation he writes: "When a very minute star or a faint nebula is not to be seen at once, do not give it up without trying oblique or averted vision, turning the eve toward the edge of the field, but keeping the attention fixed ou the centre, when the object ought to appear; this device, with which astronomers are familiar, is often successful; its principle depends probably 011 the greater sensitiveness of the sideß of the retina." The Number of Visible Stars. The reference made by Sir John Herschel as to the case with which a false impression may be formed as to the number of stars visible to the naked eye suggests that a few remarks on this subject may be of interest to readers. In the first place it must be borne in mind that people differ greatly aB to tJr- sharpness of their sight; it may or may not be true that a person with normal sighj; can see a star of the sixth magnitude but it is certainly true that many find fifth-magnitude stars at the limit of their vision while others can certainly observe stars fainter than the sixth. An important factor also is the average state of the atmosphere, as moisture and dust teud to cut off light aud thereby impair visibility; it is largely this reason that modern observatories are generally erected at high altitudes above sea-level. The conditions of observation as a rule improve as we approach the equator; this statement may be-illus-trated from particular counts of , the stars. Argelander has published an exact catalogue of 'the stars visible on the horizon of Berlin during the course of the year; it contained 3256 stars (as showing how greatly the sight of one observer may differ from that of another, M. Heis affirmed that his sight is so penetrating that he can perceive with the naked eye 2000 more starß than those catalogued by Argelander). According to Humboldt "thero are 4146 stars visible on the horizon of Paris in the whole course of the year, while Guillemin states that 4638. may be-seen with the naked eye at Alexandria. It is by no means easy to ascertain the total number of stars which may be classed as of magnitude 6 or less. The British Association Catalogue, which purports to include all visible to the naked eye contains nearly 5900 stars; these form the basis of Proctor's large Star Atlas which, though published more than half a century ago, is probably still the best one available for the amateur astronomer. Different works •on astronomy give numbers which do not agree.with'the above and no definite statement can apparently be given. A Peculiar Variable Star. Great interest attaches to a variable star, recently detectod by Mr H. van Gent, which runs through its series of light changes iu 100 minutes —a period remarkably brief compared "with that of any other variable star. A study of it has been made by Mr H. L. Alden with the Yale 26in refractor at Johannesburg. He finds that the intensity pf luminosity changes from 14.05 to in apparent magnitude, i.e., it is more than .two and a half times as bright at its maximum as at its minimum. The light varies in a most perplexing manner; it falls one complete magnitude during the seven minutes after it has attained its greatest luminosity, then for 40 minutes its light remains constant, and the remaining 53 minutes' of its period ate expeuded while the star is climbing up again to ( its brightest. It is difficult to account for these peculiar light-changes by any species of eclipse, and the behaviour of the star does not conform at all to that of the sepheid variable. The brevity of the' period, the rapidity of the. fall in intensity, and the slow recovery of brightness show that- Mr van Gent has happened upon a most unusual star; 1 which, will well repay further study in a more poworful telescope than that used at Johannesburg.