GLORY OF THE STARS.

New Zealand Herald, Volume LXVIII, Issue 20887, 1 June 1931, Page 14

GLORY OF THE STARS.

THE HEAVENS IN JUNE. ; VARIABILITY OF EROS. INTERESTING PHENOMENA. BY CRUX AUSTRALIS. The Sun will be in the constellation Taurus until June 21, when it will enter Gemini, its altitude at noon .as seen from Auckland will decrease from 33deg. at the beginning of the month to 29$deg. on June 27, then remaining practically the same for the remainder of the month. The winter solstice and the shortest day occur on the 22nd. Very little spot activity was witnessed on the Sun's disc during May. The Moon in the course of its monthly circuit of the sky will be in conjunction with the various planets as follows: — Saturn, 4th, 6.30 a.m.; Venus, 14th, 7.30 p.m.; Mercury, 15th, 8.30 a.m.; Jupiter, 18th, 4.30 p.m.; Mars, 21st, 4.30 p.m. The Moon will occult two stars, as seen from Auckland, during the month. On the 23rd Eta Virginia will be occulted at 5.10 p.m., 'and 50 B Scorpii will disappear behind the Moon's limb at 11.2 p.m. on June 27. Mercury is at present near its greatest elongation in the morning sky, where it can be seen shortly before dawn. During the month it will gradually draw closer to the Sun, with which it will be ji superior conjunction on the 29th. Venus is drawing closer to the Sun in the morning sky. It is still a prominent object and can be seen early this month lying close to Mercury. Mars, in Leo, is steadily becoming more remote from us and accordingly has lost its interest as a telescopic object. On the evening of June 8 Mars will pass less than a degree north of the brilliant Hegulus, in the constellation Leo. On the 16th, at 10.30 p.m., Mars will be in conjunction with Neptune, the latter, which can be seen with a small telescope, then being half a degree south of the ruddy planet. The brilliant Jupiter, in the constellation Gemini, is now drawing very close to the Sun, and therefo-s cannot be favourably observed telescopically, though still visible as a brilliant evening star. Places of the Constellations. The constellations may.be seen in the positions given below at 10 p.m. on the Ist, 9 p.m. on the 15th, and 8 p.m. on the 30th of the month. Low on the north meridian the bright red Arcturus, in the constellation Bootes, is prominent, with Coma Berenices, a hazy cluster of stars, to the left of this. Leo, containing the bright Regulns, is setting in the north-west with Virgo above, the brightest star of which, Spica, can be seen on the meridian above Arcturus. Further south the long group of Hydra runs beside Virgo and Leo from the zenith to the western horizon. Between the middle of this and Virgo lie the sntoll groups of Crater and Corvus. Hercules is rising in. the north-east, and between this and Bootes the striking little semi-circle of Corona can be seen, with portion of Serpens above. Ophiuchus is well above the eastern horizon, with the remainder of Serpens below it and the first stars ot Aquila just rising due east. Libra lies above Ophiuchus and close to the zenith. In the southern portion of the sky we find the large group of Asgo occupying the greater part of the south-western sky, the brilliant Canopus being just above the south-western horizon, with the remainder of Argo, following the Galaxy, situated above it. Between Argo and the zenith the Cross can now be seen at a good altitude, surrounded by the brilliant group of Centaurus. The small groups of Chameleon and Musca are south of the Cross, with the circumpolar group of Octans to the left of those. Hydrus is below the pole on the southern horizon, with Reticulum and Dorado to the right and Tucana to the left. In the south-east Sagittarius is prominent, with the first cf Capricornus on the horizon below. The pretty asterism of the Southern Crown lies just above Sagittarius, and between the latter and the zenith is the splendid group of Scorpio, containing the red Antares. Lupus lies between Scorpio and the zenith, with Ara and Triangulum below. Below these again lie Pavo and Indus, and Grus lies just above the south-south-eastern horizon. The Variability of Eros. In this column recently the opposition of the minor planet Eros was discussed, and an explanation was given that the nearness of that small body would afford astronomers an opportunity of re-measur-ing the scale of the solar system. It has long been known that the light of Eros was variable, and as it shines by reflecting the Sun's light, it seemed that either the surface of its disc consisted of a dark area and a highly reflective area, or that the small body was not 'a sphere but an egg-shaped body which alternately presented to us a circular and an elliptical appearance in the course of its rotation.

The variability in I he brightness of this asteroid has been 'studied since 1901 and many interesting changes in the type of its variability have been noted. At first the amplitude of the variation was one magnitude, with two unefpial minima in a period of over five hoirs. The variation grew smaller and in 1907 and in 1914 it was nearly absent; by 1919. however, it again exceeded one magnitude. The variation wns found to be large at the present opposition, so that the planet was sometimes one and a hall magnitudes fainter than predicted. This variability and the absence of proper sfar charts contributed to prevent many observations being secured in the Dominion, although an elaborate observing scheme had been planned. This .unexpected faintness of Eros, however. did not prevent the observers at the world's biggest observatories from carrying out their original programmes, although, in addition to accurate photographs of the position of Eros, extra observations bad to be made of the brightness of the body.

It is therefore not surprising that in the past few months,,numerous estimates of the range and the period of variability of Eros have been published. From discrepancies among the various estimates it seems thai the asteroid is not. viiiying with mathematical regularity. This view has added value lent to it by the publication of results obtained at Harvard Observatory at the beginning of this year, showing that Eros varied by over one magnitude in December and that the amount, of its variation had steadily dropped until, on January 18. its range was only half a magnitude The latest stage in the drama was the publication of a message, with the names of three prominent astronomers appended, stating that Eros had been observed to be an elongated body, the elongation appearing to rotate in a period of 5J hours. It thus appears that an important and unlooked-for fact has been discovered. If this elongation of the rapidly-spinning body is established, may wo not. look for an ' ultimate fission into two distinct bodies, in a manner similar to that in which till Earth is believed to have cast off its satellite, the Moon ? The prospect Offers a field for fanciful imaginings and it seems certain that at least some new light will lie thrown 011 the. astronomical theories of the breaking up of rapidlyrotating bodies to form satellites. Although it had been suggested and forgotten that, perhaps another asteroid, Abundantia, was double, tho latest discovery will strengthen Eros in its position as the most unirjue minor planet in the solar system—unique because of its near approaches to us and because of its peculiar shqpe. It is interesting to note that Innes, a South African astronomer, haj recently intimated that Eros was suspected to be elongated when observed there in 1924, although the matter had not been made public, perhaps in the hope of obtaining later confirmation of a somewhat doubtful observation*