ASTRONOMICAL NOTES

Evening Star, Issue 22688, 30 June 1937, Page 15

ASTRONOMICAL NOTES

THE SKIES m JULY [Written for the' ' Evening Star ’ by A. G. C. Crust, M.Sc.] POSITIONS OF THE STARS Local Sidereal Time, IGh, Latitude 4Cdeg. S. Tho following star positions bold good locally four minutes earlier each evening, as at 9.30 p.m. on July 3, 8.30 p.m. on July IS, and 7.30 p.m. on August 2: — The brilliant Canopus is now situated in the S.S.W., at an altitude of 13deg, while the highest of our bright stars is Alpha Centauri, S.W. by S., 71cleg. Alpha Cruels is now S.W., 56deg, Spica N.W. by W., 42deg, Areturus N.N.W., 20dog, Antares N. by E., 69deg, Altair N. by E., IGdeg, Eormalhaut S.E. by E, 12deg, and Achernar S.S.E., ISdeg. It will bo noticed that our nearest neighbour among the stars. Alpha Centauri, and the distant orange giant Antares, in the Scorpion, are nearly at the same altitude, and practically on opposite sides of the zenith. Also the three stars representing the three Christian virtues—Eormalhaut, Achornar, and Canopus, are about equally spaced at low altitudes from S.E. bv E. to S.S.W. Tho Earth will be at the point of her orbit furthest from the Sun on July s—i.e., she will be in aphelion. The Moon will pass the planet Saturn on tho evening of July 1, and will reach last quarter early on the 2nd, while a conjunction'with the planet Venus will occur on tho sth. New Moon falls on the afternoon of July 8, and at 8.50 p.m. on the 13th onr satellite will he situated W. by N., 20deg. First quarter occurs on the evening of the 15th, the Moon passing one degree south of Spica at midnight, while a conjunction with Mars falls on the forenoon of July 18. Tho planet will bo o.7deg south of the Moon. At 8.30 p.m. on the 18th the Moon’s position will be N. by W., 63deg, she will pass 4deg north of Antares early the next evening, and 4deg north of Jupiter, the brightest planet now visible in tho evening sky, on the forenoon of the 23rd, her position at 8.10 p.m. that evening being E. by N., 34deg. Full Moon occurs by midnight,f and on the 27th the Moon passes 28deg north of Eormalhaut. The morning of the 29th finds her once more in conjunction with Saturn, the planet being Bdeg to the north, and last quarter occurs again on tho morning of July The planet Mercury will bo in superior conjunction with the Sun on July 8, and on the 31st ho will pass O. north of Regains. He will be visible in the morning sky after superior conjunction. The planet Venus is a brilliant object in tho early morning sky. The planet Mars continues to be favourably placed for observation, though his distance from the Earth is increasing. Recent observations have shewn very disturbed conditions’in the northern hemisphere of Mars. In June the north polar snow cap broke up and disappeared, but a large and persistent white .area, probably snow, covered the Propontis, in latitude 45deg north. There were other white areas in the north, but more settled conditions prevailed in tbe southern hemisphere. There Was "evidence of a sandstorm, however, just north of the Mare Sirennm, on June 10. The position of Mars ■changed from N.N.W., 62dcg to N. by W„ Godeg, during the month, at 16h S.T. At 9.30 p.m. on July 3, Mars presents to our view the whole of the great desert area named Arabia. It will then be seen that, like our Pacific Ocean, it occupies practically one-half of the surface of the planet. The following dark areas are also visible on its margins:—Arethusa Lacus in the north, Asclcpius Lacus in the N.E., Syrtis Major in the E.S.E., Margaritifer Sinus in the S.S.W., and Acidalium Ala re in the N.W. At 8.30 p.m. on the 18th the bright areas visible include Elysium N.W. of the centre, and Arcadia N.E. of the centre, while tho dark areas comprise the Propontis, which may be snowy, north of the centre, the Trivium CharontiS west of tho centre, and the Ala re Sirenum in the south. On August 2, at 7.30 p.m., the bright areas are Arabia east of the centre, Ophir in the S.S.W., and Tempo in the N.W. Of the dark areas, the pear-shaped Acidalium Alaro is north of the centre, and the Margaritifer Sinus is in tho S.S.E.

The planet Jupiter is also well placed for observation at convenient hours, -bis position at IGh S.T. changing from E, 38deg, to E. by N., 42deg, daring July. His four bright satellites may be watched with quite a small telescope. In the following description the time is counted from midnight to midnight, so that July 1:15:27 means 13.27 p.m. on July 1, in New Zealand standard time. The innermost satellite, 10, will be in superior conjunction for the first time on July 1:15 :27, and for the eighteenth time on July 31 .T 7-48 The second, Europa, is in superior conjunction for the first time on July 1:00:18, and for the ninth time on July 29:15:19. The third satellite, Ganymede, is in superior conjunction on July 2:07 :37, and for the fifth time on July 30:20:44, while the outermost, Callisto, is in superior conjunction on July 10:09:27 and July 26:23:40. At superior (geocentric) conjunction the satellite is directly behind Jupiter as seen from the Earth. To find the apparent period for the month it is only necessary to divide the time between the first and last superior conjunction by one less than the number of conjunctions. The epoch of elongation east occurs one-quarter of a period after superior conjunction, that of elongation west ono-quartor of a period before. For Ganymede, greatest elongation east occurs on Sundays, greatest elongation west on Wednesdays,', while Callisto is furthest cast on July 14 and 31, furthest west on July C and 22. As regards his proximity to the Earth, Jupiter will be best placed in July, for he is in opposition to the Sun on July 15. The planet Saturn will he stationary in the morning sky on July 18. Decent observations of b 2 Carinae suggest that its variation is rather irregular. A minimum of Gamma Scrpontis is predicted for July 11-27, arid those of 84 Velorum for July 2, 13, and 24, in the early _ mornings. The interesting colour variable Beta Herculis is well placed at 16h S.T., and culminates about half an hour later. Its primary minima, which are the colour maxima, begin on July 8d 13h, and 21d 03h. They last about 2d lOh, so that the abrupt change on July 10:23 should be easily observable. From the Queen’s Gardens, Dunedin, at 16h S.T., Arcturus will appear rather low over the Burns Hall, Achernar low in the opposite direction. Antares high in the direction opposite to that of Vogel street, and Altair over the seaward end of Lower High street. The Moon will shine down Dowling street from a rather low altitude at 8.50 p.m. on July 13, and will be moderately low over the Early Settlors’ Hall at 8;10 p.m. on the 23rd. At 16h during the month Mars will he high and approximately over Burling-

ton street, while Jupiter will he at a moderately low to moderate elevation, over the Early Settlers’ Hall.

CONSTELLATIONS OF THE SOUTH RECTANGULAR ZONE. lI.—LUPUS, THE WOLF. Part of this beautiful constellation has boon reseribed already, as it extends into the South Circumpolar Zone. Those stars mentioned as “ already described ” belong to that portion. In tho South Rectangular Zone there are four stars of the third magnitude m Lupus. Alpha, in tho square 176,22, has been mentioned already. Beta, of mag. 2.8 and typo B2p, in tho square 179, 18, is a spectroscopic binary whoso spectral lines become double twice in every revolution. , Its light takes 270 years to travel to our eyes, and it may bo regarded as a pair of stars of sunpowers 300 and 170, temperatures 23,000 and 16,000 deg. absolute, and diameters 3.2 and 3.0 times that of the Sun. The period of revolution has not been determined. Delta Lupi, of mag. 3.4 and type 82, in the square 183,16, is also 270 light years distant. It,is also blue in colour, with a temperature of 17,800 deg. and a diameter 3.5 times that of the Sun. Occupying the square, 186,16 is Gamma, of mag. 3.0 and type 85, 250 light years distant. It requires rather a powerful telescope to show Gamma as a double, star. Its components are of mags. 3.6 and 3.8, and their period of revolution is 104 years, their mean separation being 46.7 times the distance from the Earth to the Sun. This resembles the distance from the Sun to Pluto, the most recently discovered outer planet, and amounts to 4,340 million miles. The two stars are of sun powers 190 and 160, and their blue colour indicates a temperature of 19,800d0g., giving their diameters as 2.8 and 2.5 times that of the Sun. In this part of Lupus there are also 15 stars of tho fourth magnitude. lota, of type B 3 and mag. 4.1, also in the Circumpolar Zone, is distant 470 light years and is light blue in colour, its temperature being 13,900 deg. It is 440 times as bright but only 5.6 times as wide as the Sun, and its position in this zone is 171,21. Tan 2 Lupi, or mag. 4.5 and typo FB. is a close binary of mags. 5.2 and 5.3, and its radial velocity varies in a period of 3,043 days. Its distance from the Earth is great but very uncertain, and the position is 172,20. Rho, which may be mapped in the square 175,24, and also belongs to the Circumpolar Zone, is of mag. 4.1 and. type 85. It is 230 light years away, 100 times as bright and 2.6 times as wide as the Sun. Omicron, in the square 178,19, is of mag. 4.5, and is both of the same type and at the same distance as Rho, but slightly lower in temperature, Rho being at 15.000 and Omicron at 14,100 deg. Omicron is 75 times as bright and 2.3 times as wide as the Sun. mentioned, is in tho square 180,22. In the square 181,20, may be mapped Lambda, of type B 3 and mag. 4.4, a very close binary of magnitudes 5.0 and 5.4, the colour of which has not been analysed, but the results given conform to the usual spectral relationships iu visual binaries. The light from Lambda takes 360 years to travel to our eyes, and the two components are of sun-powers 110 and 76, temperatures 15,200 and 13,300 deg, and diameters 2.6 anti 3.5 times ‘tiia/t of the Sun. Kappa, in the square 181,24, and Mu, in the square 183,23, have been mentioned already. Recently Mu has been suspected of slight variations. Only a few stars iu Lupus, were far enough north to be numbered by Flamsteed. Of these, 2 Lupi, of mag. 4.4 and typo KO, in the square 183,5 belongs also to the Equatorial Zone. Its distance is 270 light years, and its yellow colour denotes a temperature of 3,620 deg. It is 107 times as bright and 45 times as wide as our Sun, but the largest star on this -list is Phi 1, of tvpe K 5 and mag. 3.6, in the square 184,11, distant 190 light years, and having a diameter 61 times that of the Sun, or no 'less than 53 million miles. Its orange colour indicates a temperature of 3,360 deg, and its sun-power is 120. Our next star is Epsilon, of tvpe B 3 and mag. 3.7, in the zone square 184,20. Through the telescope is appears as a binary of mags. 3.9 and 6.0, separated by a distance of one second of arc. At its great distance of 300 light years, this represents a separation of at least 90 astronomical units—i.e., 90 times the distance from the Sun to the Earth. The spectroscope, moreover, shows the bright star to be a double-lined binary, of which little is known. Further information may bo obtained in New Zealand soon, as slight variations are suspected. In the meantime we may take the sunpower of the bright pair of stars to be 210, that of the companion 30, and the colour analysis gives this companion a temperature of 28,000<leg, its diameter being 0.9 of that of the Sun. The division of the spectroscopic binary remains uncertain, but the probable temperatures arc 24,000 and 15,000 deg, and the diameters 2.0 and 2,2 times that of the Sun. Another of the few large stars in Lupus is Omega, in the square 187,18, of mag. 4.3 and typo K 5. This star has an eleventh mag. companion at a distance of 12 seconds, with the same proper motion. As the distance of the system from the Earth is 220 light years, this separation.of 12sec represents an actual separation of at least 800 astronomical units. The large star is an orange giant of sunpower 80 and temperature 3,330 deg. its diameter being 54 times that of the Sun. Tho light of the companion is really rather feeble, being about, oneseventh of that of our Sun.

Ohi Lup., of type B 9 ami mag. 4.1, is a double-lined spectroscopic binary distant 270 light years, which should be mapped in the square 180,9. The colour gives a temperature of 10,900 degrees, and the system probably consists of two stars of equal temperature, sun-powers 90 and 50, and diameters 2.1 and 1.6 times that of the Sun. In the square 191,14 we insert Eta, of type B 3 and mag. 3.6. This star is 360 light years away and travels through space accompanied by a star of mag. 7.7 at a distance of 15 seconds. The actual distance of this companion from its primary is no less than 1,660 astronomical units. Eta is a blue star of temperature 17.300d0g. sun-power 410, and diameter 4.8. Its companion is nine times as bright as the Sun. Finally, Theta, of mag. 4.3 and type 113, in the square 193,12, is distant 230 light years, and has a temperature of 14,700 deg, is 86 times as bright and 2.4 times as wide as the Sun.

A very noticeable feature of Lupus is a series of stars grouped in the form of a large capital S. These are Mu, Kappa, Pi, Lambda, Epsilon, Omega, Gamma, and Delta, together with others of the fifth magnitude, and they include an exceptionally large number of visual double stars. Beta Lupi and Kappa Ccntanri, though in different constellations, form a bright “ nakedeye ” double. The genitive form of the name of this nsterism is “ Lupi,” and the contracted form “ Lup.”.