ROUGH ASTRONOMICAL NOTES.

Evening Star, Issue 4244, 3 October 1876, Page 4

ROUGH ASTRONOMICAL NOTES.

Octobeb, 1876. The surface of the Sun is very quiescent at present. Ho spots of any magnitude have been visible for a considerable time. His meridian altitude, meridian | assume, mug, and at Dunedin, m N.Z. mean time, are as foiiows : -

PHASBS 09 THE MOON. Full Moon, 3d. lOh. 26m. p.m. Last Quarter, lOd. 91i. 49m. p.m. New Mooh, 17d. 9h. 27m. p.m. First yuirter, 25d. 7h. 25m. p.m In Perigee, lid. 3h. a.m. In Apogee, 24d. lOh. p.m. Greatest N. Dec, 9d. 2h. p.m. Greatest S. Dec, 23d. In. a.m. Mercury is in inferior conjunction with the Sun on the 13th, and at his greatest elongation (19deg. west) on the 29th.

Venus and Mars are morning stars. Jupiter and Saturn are evening stars. Jupiter enters Scorpio on the 3rd, and on the lS'.h he will bo near the fine double star Beta Scorpt Saturn i» nearly'stationary in Aquarius. Eclipses of Jupiter's first satellite, Tislble in New Zealand—

After October, Jupiter will be too near the Sun for observation of the eclipses of his satellites. Directions for finding the south pole of the heavens :—We havo no bright star to indicate the position of Hie south pole, as Polaris indicate* that of tho north pole. After a lapse of 7,000 years, Bella Argus will be near the pole, but that is too long to wait, and it is necessary to devise ionie easy method by which the pole cnu be approximate y found at the present time. Beta Hydri wns near tlw pole 2,0'i0 yeais ago, nnd although it is now 12deg. from the pole, it is s'ill the best star we possess for the purpose. It has the advantage of beins a star which cannot be mistaken, as it is the only conspicuous star iu the vicinity of the nebula minor. At *his senson it is 4detr. westward from the nebula in the evt niua, and the br ght star Achernsr 15deg. eastward. Another 3rd magnitude star, Gamma thetw >nebu!jß, Learert« the nebula maj >r, and the distance between t e two stars is i2d<"g., the same as the distance from Beta, Hydri to the pole. N<>w the pub' lies iu a risrht line joining Beta Hydri and Alpha, Crucis the principal s'ar in the Southern Cross; and if a po ; nr. i.e taken in th s lme such thnt Beta Hydri is equally remote from it and from Gamma Hydri tl at point will be the pole, nearly. With a good eye for estimating distance and p .sition, a very near approach to due south enn bo made in this >vav,

The distance b..twetn Alpha and Gama Cruci* is 6deg t/miu.

THE ABERRATION OF LIGHT. Two hundred years ago, Koenicr, the Danish aaironomer made known his discovery that lignt takes 16£ minutes to travel a disiauce equ 1 to the di-.imeter of the Earth's orbit. It did not strike astronomers that, the Earth's motion in its orbit, combined with the srrailual propagation ■ f lUht, would be likely to of the stars; for Bradley, the Kutjlish asfciouomer, fifty years afterwards, «iis puzzled for a, time to account for the shifting of the position of the stars at dillerent seasons, wl ieh he detected by means of the zenith sector. When the true explanation occurred to him, it struck him with the f«>r.-e of a certainty, and iic immediately set about the deter-minnt-ioii of its amount. It is remarkable that Bradley's first, valuation of the constant of aberration, 20nun. 25sec , is within two-teuths of n sea-nd of tho present accepted valut\2omh:.4ssec. He must hove been au accurate obsejver. In pursuing his investigations on aberration, Bradley detected another inequality which no one la.! susDected to exist—viz , the nutation of the ea.'th axis dei euding on the position of the Moon's nodes. He soon ascribed this to its true cause, and to establish it, he continued his observations over a period oi nineteen years. Thus we owe to Bradley tho discovery of two of the most troublesome inequalities which astronomers have to deal with. Iu a catalogue of stars we get their mean places, bnt they never appear in their mean places; and the deviation from the mean place is continually varying, both in direction and amount, and is d fie: ent for each star whien makes their reduction to their apparent places very laborious.

Day. Morid. On Merid, Rise*. Sets Alt. h. m. s. li. m. b. m 1 47° 22' 11 57 30 5 41 6 10 8 50 4 11 55 25 5 3! 6 10 15 52 42 11 53 40 5 18 6 S9 22 55 14 11 52 24 5 6 6 39 29 57 88 11 51 41 4 51 Q 50

N.Z. time of reappearance, E. side. Jupiter sets d. h. m. b. h. m. 8 7 2 34 p.m. 10 19 p.m. 15 8 57 9 „ 9 59 „ 31 7 It 48 „ 9 ia „