ROUGH ASTRONOMICAL NOTES.

Evening Star, Issue 4063, 4 March 1876, Page 1 (Supplement)

ROUGH ASTRONOMICAL NOTES.

March, 1876. < 1. The Sun.—A very large spot made its appearance on the Sun’s disc on the 10:h of i' bruary. During its passage ac oss t-e face of the Sun, it. underwe t great changes. On the 12th it was s ngle, the umbra being over 20,000 miles, and the penumbra 50,000 miles m length. On the 13th it was, throu.-h t h e Sun’s rotation, much better seen a: d st.ll single. On the 10th it was found to have split uu into hree spots, two very large a*d one muc> smaller. On the 20th it was broken up into six spot l *, arranged in a loi g line, the dir ct.ou of the line being nearly at right angles ti tbe direction of t' e longest diamet. r of the spot ten days before. This was a finer and more interesting Sun spot than any that hj s appeared t r the last two or three 3 ear?. The Sun enteis Ari's at half-past five oa the afternoon of t se 20th, and Autumn is then supposed to comme- ce. An. annul r ecipse of the Sun will take place on the 26th, but it will not be visible in Dunedin.

2 The Moon will be in Perigee on the 6th at lam.; in Apo ee, on the 18th, at 11 a m.; and again at least distance from the Earth on the 30th a 1; 9 p.m. Tbe phases will take place as follows:

First Quarter on the 3rd, at 9h. 17min. p.m, Full Mr on on the 10th, at sh. 43min. p.m. Last Quarter ori the 18th, at Oh. 54min, p.m. New Moon on the 261 hj, at 7h, 42iniu. p.m.

There will be a patti >1 eclipse of the Moon on the eve ing of Mi.rch 10. Phenomena of the eclipse First contact with the Penumbra, 3h. 27min. p.m. First cont ict with the shadow, 4li. 51miu. p.m. , Middle of eclipse, sh. Slmin. p.m. Last contact with shadow, 6h. Slmin. p.m. Last contact with Penumbra, Bh. IGpiin. p.m. Seeing fh t the M"on does not rDe till halfpisl six, and t at the eclipse is but asm -11 ope, it is plain that there will n> t be v-ry much to see on this occasion. As the Moon rises, a small black ‘ notch ” will be seen in the southern | art of ? ht r disc. She wil 1 , too, appear dimmer than usual for abou o an hour after risinr, and that will be all.. 3. ai eroary.—E irly risers will have a good opportunity of seeing this p a et about the 10th of the month, when it will be at i s great, st elongation we-1 (27° 30'). Ah that time Mercury will rise about two hours before sunrise, con iderably to the south of ih< Sim’s track. He will ta*-n be about 2° north of the star Delta Capricomi. On the morning of the 18th he_ will be in conjunction with >a urn. By ir-ing a low-power eyep ece with a ve yla-ge field it may be possib'e just before sunrise, to observe the two p'anets together. 4. Venus is still iu< teasing her angular distance f.om the Sun, but almost pari passu her North Declination is incrta ing. Her altitude alove the horizon at sunset is, therefore, not yet sufficient to admit of her be ng observed satisf >« tor ly. She can be sem very soon afte ■ subset f»r to the north of the Sun’s ir.ctc. Her gibbosity is rapi ly decreasing, and she will iu a couple of months’ time be in her half-moon phase.

5. Marsjiow looks like an ordinary first magnitude re 1 star. He is in the 3.\V. comer <-f the c .nstellnti m Aries. He may be seen north of west, and mar the horizon, soon aft> r snnsA. Mars Will be in conjunction wiih Venus on the 30th.

6. Ye ta. —This m’n r pi net wi'l bi hi oppodtion t > the Sun on the 29th, At that time it will follow P»i Vir-v-'nis (a fif-.h magoi ude st-r, which can be found by means of a stir m : ‘p) about four minuet As V sta sines with a brightness equal to that of a 6.J magnitude dar, she should be visible to the naked eye in ve y fine weather. At all events, an opera-glass will show her distinctly : the largest telescope would do lit'le more, 7. Juno will be n opposition on the 28th. She is n'it nea ly so bright as Vesta. At the I eri -d mentioned she wi I be.found about 1° S. of the double s‘ar Gamma Virginis, Her proper mo i n will serve to distinguish her liom neighboring small s! a s. 8. Ju:. iter is in Scorpio, close to the double star Beta of that consr.ellation. In fact the star and the planet are in the same telescopic field. Jup t r rises just before ten o’clock. The following table of the phenomena of J unit ;r’s satellites may perhaps be useful' Only those phenomena which will tike place more than an hour after Jupiter’s rising, and also before midnight, will be noticed. The lime use f is mean New Zealand mean time, or the time at the meridian 172° 30' east of Greenwich.

N.B.—The transits of the Satellites and their shadows cp.u be seen with telescopes of less than 3in. aperture only in very fine weather. 9. Saturn rises in the morning shortly before the Sun. It will be possible to jget a Jair vigw pf him towards ,the end of ihe month. 10. Uranus is not yeyy far from where he was I'fit month : he is certainly Very quite as bright as a s.J'magnitude star. 11. .Neptune is unfavorably p tuated for observation. The Southern .Constellations,

I. THE SOUTHERN CROSS. This small but very fine constellation passes .the jneridian at ni'diiight toward - 1 1© end of the month. It is, therefore, favorably situatt d for observation during our autumn evenings. The “ Crosi ” is so wd known that no directions for finding it nee I be given. DOUBLE STARS. '

1. Its principal star Alpha Crucis (“ the foot of the Cross”) is of the fir*t magnitude an-l double. It may be thus briefly described. Bight Ascension 12ors I9miu ; declinarion 62° 25' S.; magnitudes. 2.2; position* 118°, distance, 6" ; color, both bluish white A moderat ly high magnifying power, 70 say, u*ed with a two-inch telescope, shows it double, The fwo stars are of nearly equal size, the preceding (that which first leaves the field of view) being somewh ri brighter th n the other. This is the finest “ p.dr ” in the heavens. At a dis tan e of 87" from th-j larger star of the double with position anrie 201° is a 5J mag star of a sea-green color Forty years ago Sir John ■ lerschel thoughtthathis observations of Alpha Crucis, made at the Cape of Good Hope, give him reason to believe that this star was a pretty rapidly moving “ binary.” Time, however, has not confirmed this opinion. If the distance aud position of the two stars have

changed at all it ia to a ve y Hina 1 extent. The spectroscope shows that this st tr and the next belong to the same clans as Tinus, that they are i “hydrogen stars,” that is to say their spectra E rove the existence < f enormou- quantities of ydrogen in the a'mospheres which surround them. It should be menione 1, however, that their hydrogen lines are relatively much f outer than those of Sirius, CLnopus, and Foiualhaut, 2. Beta Crucis, R.A 12hrs 40miu ; dec; SO 5 !'8.; mags. 2 —l, 8, pos, 259°, distance 2'4, .col, white, crimson. (Distance taken by differ®nc® df R.AA This star is the rifeh • aim of , 9 , 08S * Herechel says that the small star looks just like a blood drop on the sky. ' A three-inch telescope shows the color well. Gamma Crtfcis, R. A. 12hrs 24min; dec. 5$ 2b S. i nwfc. 2.5.; poll, 37.6°; diet. 102";

C"l. reddish or nge, lucid blue. Th‘s star (the head of the Ooss), owing to the strong c ontrast between the hu s <>{ its c mponm stasis a si guL< and b a itiful object; 1c is not unlike the northern star Beta ' ygni, I ut the stars are much further apart in Gamma Crucis. The sp -ct um of thi - star is very fin >, it res’ mbh s the spectra of Bett-lgeuse and An t ires, bit the dark lines in it are much more “ pronounced.” Iron, ma >nes um, and sodium app ar to ab und in all the e stars, while hydrogen se mi to be wanting, or, rather, not abundant.

4. 126 Dunlop, B. A. 12hrs 46min. dec, 56° 30' R. ; mags 5J.6; pos 16°; diet. 38" col., blush white, greenish wnite. This fin l double stir forms a near y equilateral tnang ewith Gamma a>>d Beta Crucis, and follows the former star (22min.)

CLUSTERS, ETC. Kappa Crucis, B.A, 12hrs 46tnia ; dec 59* 42' S.—This is an exquisite l.tdo cluster of stars. It ia close to Beta Crucis, S and a litt e following. Seven of the principal'stars are arranged like the capitalist ter A, one-half of the crossbar of that letter being wanting. The o her half ia. c imposed of three stars nearly in a line. The inner star is of a fiery red color, the outside one yellowish green. The middle one is very remarkable; it is of a very deep green, somewhat darker than an emerald. Others of the stars, also, are colored, some being reddish and others greenish. Ou the preceding side of the “A ” there are many smaller stars. On the while this is one of the prettiest things in the sky. Herschel usea to c mpare nt to piece of fancy jewelle y. On favorable nights tbe “ A” referred to may be made out with an opera glass. A three-inch telescope shows it very we' I in fine weather, but in au 8£ Inch refl. ct r it is s rnply'superb. Sir J. He schtl mapped this cluster. In his dapr -.m he makes th i firry star smaller than the deep gr en one. At present the red star is very much brighter than ihe green one. Some changes then, are, going on with conside-able rapidity in this distan 1 congeries •£ si ars. The i ’oalSack.—This reraatkable hi ck space, which fol ows the C oss, is not, as it seems to the naked eye almost without stars. On tbe contrary, sma 1 stars a; e pretty richly strewn over Ihe whole of the dark space. In fact, the “ f'oa l Sick” is richer in stars than most parts of the heayens. Toe explanation of its comparative darkness probably is, that while stars of mo (erate size are numerous in this region, the myiiads of ve y minute stars which form the background of the Milky Way are here wanting, bear the middle of the C al Sack th-re is a small star v.sib eto the unassisted eye Close to this, in K.A 12hrs. 35min.;dec. 62° 17' S, is Dunloo 272, a pretiy group of 11 magnitude stars. Thi . g oup is extremely like the Pleiades as seen by the naked eve.

*Our distances hj ive obtained in the follow! i g way The position of the star hivin; b en taken by means of a position circle, the double star is made to transit a wire inclined to the meridian at an angle of 259° or of 101°. The duration of the trans.t is taken to e ghths of a second. Then, if T = time of transit a = angle of position of the wire. A = angle of position of the doable star. p = polar distance of the star. T, 15. sin p. cos a ~ . . . distance of stars m

sin (a—A) seconds of arc. To take an example.—The position angle of Alpha Orucis was found to be IIS 3 . Very many transits of the two stars over the 259° wire were taken, and the time was finally concluded to be between 11 and 12 quarter seconds. j Then 2i Xl 6 = 43 , 125 =. log 1*631729 Sin. p 27deg, 35min. = 9*665617 Cos a = Sin lldeg. = 9*280599 Cosec {a—A) = 39deg. 10 201128 . 0.782073 6*os4sec. of arc, or almost exactly 6sec. Th's method is Sir John Herschel’s, slightly modified to suit circumstances; it is probably the very best one for amateurs to use, and has be> n found, after considerable experience of its wo kin', to give satisf.ck »y results. If the stais are nt too do eto each other and at no great distance from the pole, v<ry gr; at accuracy may be attained by means of these oblique transits. The weakest point in this method is that the distance is n>t taken independently of the position, the latter being one of the elements used in calculating the former; with the filar micrometer, of course each measu e stands on its own merits.

4 ,1 Phenomenon. u o O -P cQ £ 8 o ol .Time. Hr « CQ h. m. a. 4 — Transit offsatellite, egress . .. III.... 11 52 0 5 “ Transit of satellite, ingress . .. I, ... 10 42 0 5 r— Transit of shadow, egress .. .. I. ... 11 41 0 11 Transit of shadow, egress ,. III. ... 11 4 0 12 — Transit of shadow, ingress . I. ... 11 22 0 14 — Eclipse, disappearance II. ... 11 16 17 16 — Transit of satellite, egress ,, .. II. ... 11 3 0 20 ■— Eclipse, disappearance .. I. ... 10 36 14 21 — Transit of shadow, egress . .. I, ... 9 55 0 21 — Transit of satellite, egress . .. I. ... 11 0 0 23 -r Transit of satellite, ingress. .. II. ... 10 59 0 23 — Transit of shadow, egress . .. II. ... 11 23 0 28 — Transit of shadow, ingress . .. I. ... 9 3S 0 28 —T Transit of satellite, egress . .. I. ... 10 37 0 28 — Transit of shadow, egress .. .. tor... 11 48 0 29 — Eclipse, reappearance. .. III.... 9 151 29 Occmtation, reappearance . .. I. ... 10 8 0 29 — Occultation, disappearance . .. III.... 11 30 0 30 — Transit of shadow, ingress .. . II. ... 11 25 0