IN STARRY SKIES

Evening Post, Volume CV, Issue 123, 26 May 1928, Page 26

IN STARRY SKIES

ARROW, EAGLE, DOLPHIN, AND LITTLE HORSE (By "Omega Centauri.") There lies an Arrow-—from what bow it Near to the flying Swan, no Poets tell. Beneath it soars the lloyal Bird ot Jove, Rais'd by his master to these realms above. * To sailors oft an inauspicious star, Rises at dawn of day, the bright Atah'. Where Capricorn his horned forehead rears, Not distant far his course the Dolphin. steers — Obedient fish—that from a distant shore His coy reluctant bride (to Neptune bore. With four fair stars lie decks the sumnfer skies, Sparkling and soft as maidens' beauteous eyes. —Aratus. Although three of these constellations are small and rather insignificant, they aro all included in Ptolemy's original forty-eight. The equator runs through the middle of Aquila pawing between the stars Eta and Theta. ' The other three lie entirely north of the equator, but even the most northerly only extends to declination 22 degree's north. They are all well situated for observation here throughout the winter. By the middle of July they are well above the North-Eastern horizon at half-past S in the evening. \ SAGITTA. Sagitta has no star brighter than magnitude 3.7, but its straight lino of stars is rather suggestive of an arrow, and seems to have been so named by the Persians, Arabians, Hebrews, and Eomans. Aratus says that no poet tells 'us from what bow it fell, bufaecording to Eratosthenes it was the arrow used by Apollo when destroying the Cyclopes, those gigantic cave-dwelling, one-eyed cannibals of whom Polyphemus was the most prominent. The Milky Way crosses this little constellation in two branches. The main one comes to it through the centre of Aquila, the other both narrower and fainter passes near the boundary between Ophiuchus and Serpens. The ancient constellation was only four degrees in length, but now it has been stretched to more than ten degrees. Some of its star fields aro magnificent when viewed through the telescope. A number of its stars are double or multiple. Beta has a close double as a companion eight seconds from it. Zeta is itself a close double, white in colour, with a ninth magnitude blue companion nine seconds away. Epsilon has an eighth magnitude companion at a distance of 92 seconds. Theta, in the head of the Arrow, is a triple star, the components being of magnitudes 6, 7.1, and 8.3. The colours are given by Webb as white, bluish, and reddish, Irat Smyth and Chambers describe them as pale topaz, grey and pearly yellow. Xi a sixtli magnitude star is the principal object in a beautiful group which contains also a very red star and a close tenth magnitude pair. Eta lies in a specially rich, region, and, in a circle round it of 40 minutes radius, there are several close pairs. Bis a variable star of the Beta. Lyra type with a period of 7.0.5 clays. S is a short period variable, ranging from magnitude 5.5 to 0.1 in 5.4 days. Tis an irregular variable with a range from 5.3 to 9.9. Uis an Algol variable with a period of 3.4 days. During each eclipse it sinks from .magnitudes' 0.5 'to 9 M7lis a, rich compressed globular ciuster in the shaft of the arrow. Its diameter is about five minutes. It was discovered by Mcchain in 1781. -Messier described it as a nebula without : stars, but it was resolved by Sir William Horschcl in 1783. Within one degree of it is a beautiful low power field containing a pair and a triple group, all of the eighth or ninth magnitude. The distance of the globular cluster I from us io believed to be ten thousand light years. AQUILA. The Eagle is easily recognised by the line, about five degrees in length, -which is marked by throe stars in the Milky Way, the centre 'one being far brighter than either of the others. Alpha is slightly brighter than a typical iirst magnitude star. It is the eleventh in the list of brightest stars, and lies between Beta Centauri and Alpha Crucis in magnitude. Its name Altair means The Flying Eagle. Gamma, or Tarazed, is the next brightest' star. The name means the "Soaring Falcon." Beta is called Alschain. Altair is the vertex of a great isosceles triangle in the sky,, the corners of the base being Vega, the brilliant gem of Lyra, and Dencb the tail of the Swan. These stars arc each about 48/dcgrees from Altair. Another, more nearly equilateral, has Vega and Bas Alhaguo for the ends of its base, and Altair again for its vertex. Altair owes its apparent brightness to its comparative nearness to us. It is only 16 light-years ,away. Theta and Gamma, at distances of 217 and 181 light years, are really far more brilliant suns. ' Altair is only about 17 times, whilst Theta and Gamma are over 300, and over 360 times respectively, as bright as our sun. Eta is, however,' far more brilliant than either of these. It is three times as distant as Gamma, and appears but half a magnitude fainter. It must therefore be in reality about six times as bright. This would' make its luminosity 1800 times that of the sun. All the bright stars in Aquila show motions of approach, some as high as. thirty miles per second. Part of this speed is of course due to the motion of the Sun. The radiant point of the Aquilids, which are seen between 7th June and 12th August, is about .5 degrees east of Altair. Eta and Thota are spectroscopic binaries with periods of 7 days 4 hours 14 minutes and 17 clays 3 hours respectively. The whole of tho galaxy in this constellation is strewn with double and multiple stars. Tho list given in. Webb's "Celestial Objects for Common Telescopes" fills five and a half pages. The field about Epsilon is very fine, containing a triplet, a pair and other stars. Mv is accompanied by a f>.int pair. Gamma has another beautiful field with a double curved row of ninth or tenth magnitude stars. Eta varies between magnitudes 3.5 and 4.7 in tho period given, above. XJ is ' another short-period variable, ranging from 6.2 to 6.9 in 7 days. S. and B. are long period variables with ranges from 8.4 to 11.8 and from 5.8 to 12 in 146.7 and 355 days respectively. The magnificent but extremely distant cluster Mil is sometimes included in Aquila, but we have already described it in Scutum Sobieski. NOVA AQUILAE No. 3. Ten years ago tho constellation Aquila became for a short time the most studied and best known in tho heavens. This was due to the sudden appearanco within it, but near the border of Serpeus, of the brightest nova that had \been seen for 300 years. It was noticed first in Wellington by Mr. G. V. Hudson on tho evening of 9th June, 1918. It was then as. bright as Altair. The Government Astronomer was immediately communicated *with and very soon telescopes throughout the country were directed towards it. From tho Wellington College Observatory it was watched throughout tho night, and photographs were taken of it. By 5 a.m. oe tho 10th it was as bright as

Alpha Ccutanri. The evening of the 10th was overcast in Wellington, but good views were obtained from Lower Hutt and Wanganui. It was then nearly ns bright as Sirius, reaching to maximum of —1.4. Then it rapidly declined, in seventeen days falling to magnitude 3.7. After that, there were the usual fluctuations as it' gradually faded. Examination of several hundred plates taken at Harvard between 1888 and 1018 showed that before the outburst it was a star of the tenth or eleventh magnitude showing slight changes in magnitude. On 3rd June, it was still of normal brightness, but on 7th June it had risen to magnitude 0. On the 9th it was 100,000 times as bright as it had been less than a week before. During one single day it gave out more light energy than it had emitted in the 250 previous years. Tlie spectrum went through all flic characteristic changes that have been described and discussed in these columns in connection with the theories of the origin .of such outbursts. By August, 1919, it had developed into a planetary nebula, and its size taken in connection with the observed rate of outrush of gas when at a maximum, was consistent with its estimated distance of 300 light years. DELPHINUS. To the north-east of Aquila i? the small constellation Delphinus, the pictured form of which is a weird creature very unlike the real Dolphin. It is also unnaturally small compared with the Eagle close beside it. On the other hand it is far larger than Equuleus, the Little Horse. The Dolphin was considered by the ancients to ,be a very remarkable fish, one of its characteristics 'being a great fondness for music. One of them is said to have found Amphetrite when she was hiding among Jhe islands of Atlas, and brought her as a wife for Neptune. As a'reward the Dolphin was given a place amongst the constellations. Another Greek, story tells/that Arion, the poet and musician of (Corinth, acquired a great fortune in Italy, but when returning was thrown overboard by the sailors who wished to secure his wealth. As soon as he found that his life was ill danger he bogged permission to:play one tune upon his lute before he died. This attracted a shoal of dolphins, and one of them rescued him as soon ts he touched the water and carried him safely on its back all tho way tc the shores of Peloponcsus. The main stars of the Dolphin, though not bright, make a noticeable little figure in the sky. Alpha} Beta, Delta, and Gamma form a slightly irregular diamond, and. Eta, Epsilon, Kappa, and lota, another rather similar figure. Alpha and Beta are known by the extraordinary names Sualocin and Eotanev, the origin of which was a puzzle until it was noticed that if read backwards they gave Nicolaus Vecator, tho Latin form of the name of an assistant of Piazzi. Alpha is a B typo star IC3 light years away. _ Beta is a close binary with a more distant .eleventh magnitude companion, 121 light years from us. -The main pair has 61 time 3 the sun's mass and its orbital motion takes 2.0J years. Gamma is also a binary. . Its components are of magnitudes 4.5 and 5.5 and are 11 seconds apart. Its distance is 125 light years. Vis a long period variable ranging from magnitude .7.5 to 17 in 540 days. "W is an Algol variable with a range from 9.3 to 12 in '4.8 days ; U is an irregular variable and S, T, X are long-period variables with ranges from magnitude 8 to magnitude 13, and with periods of 277.5, 331.2, and 277 days respectively. EQUULEUS. The Little Horse is even smaller than tho Dolphin. The Arabians called it the Part of a Horse, and the Hindus the Horseman. The Greeks took it to represent a beautiful horse presented to Pollux by Juno. There is no star in tho constellation above the fourth magnitude, but there aro many fields that are interesting when seen through a small telescope. Alpha is dignified by a special name Kitalpha, which the Arabians applied to the whole constellation. Beta is a triple star one of the components of which has a fainter companion to be seen only with largo instruments. Epsilon is a binary with its orbit almost in the line of sight, so that the pair opens and closes in 97.4' years. It is 171 light years from us. Delta is a binary star with the remarkably short period of 5.7 years. It is only 46 light years from us, and the. two stars have a combined mass less than twice that of our. sun Gamma, with small instruments, is a striking pair. Tho magnitudes of the components are 4.2 and 5.7 and their colours yellow and white. Since it is 465 light years away its components must bo very brilliant bodies giving together nearly 3000 times as much light as our sun.