The Night Sky in June

Abstract

THE summer solstice on June 22 brings the shortest night lasting, inthe northern latitude of Greenwich, less than 7½ hours, according to the sun's setting and rising, and a little more than 3 hours if twilight (nautical) be taken into account. The moon is full on June 12d 23·8h and new on June 27d 21·2h U.T. A lunar conjunction takes place with Jupiter on June 19d 3h: with Saturn on June 22d 15h and with Venus on June 30d 14h. Venus, a bright star in the evening western sky, sets at about 22½h, preceded by Mars. Jupiter rises before Oh after June 10 ; its present stellar magnitude is about –2·1, as compared with –3·4 for Venus. Saturn is reappearing in the skies as a morning star, and in the middle of the month rises after lh. About 21h in mid-June, Arcturus stands out conspicuously on the southern meridian. Lower in the south at this time will be found Spica just west of the meridian and Antares on the east. Antares, with a radius 450 times that of the sun's, has an averagemean density of only 1/3,000 that of air at N.T.P. From a radiant not far from Antares come the slow-moving fireballs known as Scorpiids. Two interesting double stars in Bootes may be noted—ɛ Bootis, having the euphonious name of Pulcherrima, is a beautiful double the components of which, separated by 2½", are a 3rd magnitude yellow star and a blue star of magnitude 6½ξ Bootis, with a period of about 160 years and an orbit of great eccentricity, comprises a yellow star (mag. 4·7) and a purple star (mag. 6·6) separated by about 4½". α Herculis provides another finely coloured pair-a mag. 3-0 orange star and a blue green mag. 6·1also separated by 4½". Between η and ζ Herculis may be seen a nebulousspot of light which is the well-known globular cluster in Hercules. Thestellar population of this spherical system is not less than 50,000 stars ; these occupy a volume of space (500 light years across) which would be able to contain the greater number of our naked-eye stars.