ASTRONOMICAL NOTES FOR AUGUST

Otago Daily Times, Issue 14282, 3 August 1908, Page 8

ASTRONOMICAL NOTES FOR AUGUST

By Jons Gbigg, F.R.A.S.

THE SUN. The path of the Sun during August will be from R.A. Bhr 45mm north declination ' n the consfollation of Cancer to R.A 10.37 to N. 8.40 in Leo. THE MOON four days old will be found in Virgo, tho periods of cliange (New Zealand time) areFirst quarter sth 9h 10m p.m. Full moon, 12t-Ji 29m p.m. last quarter, 19th 8h 55m a.m New moon, 27th ... • lOli 29 m a.m. t lie-Moon will bo in Purine-i.e., the point in its elliptic orbit whih is nearest to tho earth at the period of Full; its large apparent diameter, 33j minutes of arc, will tlioroforo bo noticeable. It will be in Apojec on the 26th. THE PLANETS, Mercury will not be visible during tho month as it is passing round from west to east behind tho Sim. It will be at its greatest distance from the earth on tho 27 th. VENUS on the Ut of August wili bo west of the ® un ' r | 3 ' n fT 2hr 17min earlier, and; as a morning star,' wil gradually increase in brilliancy till the 12th. On tho 23rd she will be in conjunction with the Moon, about sJdeg south. MARS is now absolutely invisible to us, being on the other 6ido of tho Sun, which will • be between us and tho planet, on the 22nd. JUPITER, which we have been watching with so much interest for some months past, will pass behind the Sun on the 18th. SATURN is now coming under observation, rising about 10 p.m., and reaching the meridian at 4 a-in. at tho beginning of the month, and four minutes earlier daily. The Moon will be near it on the 15t,h. URANUS. This planet may bo found with a telescope mbout 7deg north of the star 2eta Sagititarii, its path for the month being from R.A. 19hr south declination 23.8 to 18hr 57min, declination 23.13.' The Moon will bo very near it on tho 10th, and, aa 6Cen from the Cape of Good Hope, will occult it. ' PLANETARY CONJUNCTIONS will occur as follow:—l4th, Mare and Jupiter; 17t.h, Jupiter and Sun; 20th, Meroury. and Sun; 22nd, Mars and Sun. Combining these, wo may say that during tJiat week a nearly straight line will be formed in the following order:--Earth, Sun, Mercury, Mars,, and Jupiter. If the distance of the Sun from the Earth be called 1, tho distances of tho three planets will be, approximately, 1.36, 2.63, and 6.38 respectively, which may be rendered into miles by multiplying by 93 millions. The plonets Mercury and \ enus having •been objoots of interest during the past two months, we purpose to inquire what wo haw learned, and may further learn, I by our\obsorvatiorts. First, we note that j Meroury, during the early part of Juno, ap- i pea rod to be almost stationary, at a distance of 24deg oast of the" Sun, and was easily seen by the' unaided eye. During the rest of tho month it approached the Sun, becoming brighter, until it was overpowered by tho Sun's rays. In a short time it reappeared west of the Sun in the morning twilight. On the 25th July it had reached its maximum distance west 20deg, and is now disappearing behind the Sun. Early in Octobor wo may expect to find it similarly placed, with regard to tho .Sun, as it was in June, 119 days before. Thus we have gained a rough idea of the sine and period of its orbit. A correction must, however, bo made for tho motion of tho E&th (our point of view) in the meantime, which has boon travoliing ill the same direction as tho planet, though at a less speed It may be found by calculation that, tho actual year of Mercury equals about 89 of our days. Venus also lias passed between us and the Stin, and, by a rare coincidence, almost at the same time as Mercury. The former, b?ing much larger and nearer to us than the latter, ite brightness was intensified, and thereby we were bettor able to watch its progress with the naked eye; while with t.lio teloscopo the increase of apparent diameter, which always accompanies decrease of distance, was very evident, that of Yonus subtending one minute of arc, and Mercury 12 seconds. Wo have invited attention specially to these two planets because their recent movements and beautiful appearance in the evening sky afforded an opportunity of trying to make dear a problem whioh is often found somewhat difficult to tho uninitiated—viz., to observe tho orbital motion of tho two inner planets. By following up our observations of tho outer planets we shall find that each makes regular journeys ,from and towards the Sun, showing that they, as well as our Earth,' rcvolvo in planes very slightly inclined to each other. THE STARS. The following bright stars, as seen from Duticdin, will culminate at the hours najned on the Ist of the month, and 3min 56sec earlier daily afterwards: — Altitude. A returns ... 5.41 p.m. 25 N. Ant-arcs ... 7.53 p.m. 70 N. Canopus ... 9.51 p.m. 9S. (lower transit) » Vega ... 10.3 pjn. 6N. Altair ... 11.15 p.m. 36 N. These times are calculated for tho meridian of Port Chalmers, and reduced to Now Zealand standard time—llhr 30min fast of Greawioh. For inland places on or about the same latitudes ouo minute should be addod for evory 12 miles westward. If a compass is used for finding the meridian, allowance must be mad© for its variation, which is given as 16.48 east of true north. ENCEE'S COMET. No observations of this comet have yet come to hand, though it has been sought for by many enthusiastic telescopists in both -hemispheres. It was due at perihelion at tho end of April, and is now doubtless far on its outward journey again. lis period is three years and a-thiirl, so that at each suoressi-re return to the neighbourhood of tho Sun, the Earth is in a different part of its orbit, and when it happens that the' distance is considerable the comet, being a small and faint object, is invisible. For other reason*, some of which are as. yet imperfectly understood, it appears to undergo changes in form ami intensity, so that no very groat, surprise is felt when it does not mako its appearance just when and whero expected. It was observed at Thames New Zealand, in February, 1895, June' 1898, and ' N'ovcmbor, 1904. The first announcement of tho discover}of this comet, as such, was made by Pons, of Marseilles, in 1818, but- it was aftorwards found recorded in observations as far hack as 1766. M. Knckc, of Berlin, having examined all available records, com- 1 puled the orbit, and predicted its return in J 182:1. The prediction was verified in Australia by its reap|>eariince in that, year, since which time it has been regularly observed. ( Its orbit does not extend to the distance < of .lupitor's; henco the attractions of the i eevcral planets whose orbits it crosses are i very noticeable. This fact has been utilised i by matheniatieiaiis for "weighing" the 1 planels, and has also led to the supposition j; that, a '• resisting medium " may surround I < the Sun. i