The Sky in September

Abstract

As an offset to the perceptibly shortening days, September provides in the latitude of the British Isles unexcelled night skies to those who search with binoculars or merely use their oyes. By the middle of the month at 21h U.T. (- 22h Summer Time), the great triangle formed by Vega, Deneb, and Altair is not far past culmination, whilst crossing the zenith obliquely to the meridian is the Milky Waya brilliant sight when the moon does not interfere. Arcturus, nearing the north-west horizon, is balanced by Capella in the north-east, and after midnight the Pleiades, Aldebaran, and the head of Orion make the low eastern sky conspicuous. There are also other gems, such as the tiny constellation, Delphinus, the double star cluster in Perseus, and the well-known double star, p Cygni. The moon is full on September 12 at 12h, and in this lunation becomes the ‘harvest moon’. On September 7 it occults X Sagit-tarii (magnitude 2-9), the disappearance of the star taking place in twilight at 1911 29.5m and the reappearance at 20h 35m. Saturn is the only planet at all well placed for observation; in the middle of the month it transits about 23h. The ring system appears about half-way open. On September 12d 3h, the planet is in conjunction with the moon. Venus is at inferior conjunction with the sun on September 8, when the planet passes 8° south of the sun's centre; a thin crescent may then be observed telescopically. The variability of Algol (P Persei) may be observed within about lj hours before and after the following times: September 4d 23.6h, 7d 20.4h 25d 1.3h, 27d 22-111 and 30.1 18-&1. The sun enters the sign Libra (Autumnal Equinox) on September 24d 0h.