The Night Sky in September


    THE sun crosses the celestial equator at the autumnal equinox (or First Point of Libra) on September 23 at 17h U.T. The moon is full on September 9 at 20-lh and new on September 23 at 20 -6h. For a few days near full phase, the moon rises only 21-23 minutes later on successive evenings instead of the normal 50 minutes in these latitudes-hence the Harvest Moon. The moon occults two naked-eye stars during the month, namely: (1) δ Piscium (mag. 4*6) on September 11, when its reappearance from behind the moon's disk, as seen from Greenwich, takes place at 22h 40-6m U.T. at position angle 238° from the north point; (2) ε Tauri (mag. 3-6) on September 15, the disappearance taking place at 22h 32.2m at 131° and the reappearance at 23h07.5m at 211°. The respective times and position angles as seen from Edinburgh are 22h 35.4m (118°) and 23h 18.9m (224°). Lunar conjunctions with the planets occur as follows: with Jupiter on September 8 at 7h; with Saturn on September 12 at 8h; with Mars on September 22 at 14h and with Venus on September 27 at 9h. Mars, a morning star difficult to see, is in conjunction with Mercury on September 4 at 20h and September 16 at 15h; on September 5, Mars is near the first magnitude star Regulus. Jupiter is a bright object rather low in the night sky and southing at about 22h in mid-September. The various phenomena of the satellites may be followed with the aid of the tables and diagram given on pp. 616-617 of the Nautical Almanac for 1938. The four bright inner satellites, visible with binoculars, are most closely grouped near the planet at 22h 15m on September 1, 7 (all eastwards), 8, 10 (one satellite occulted), 17 (the same satellite again occulted by Jupiter), 18, 25 and 26. Saturn, which is now visible throughout the night, souths at about lh 30m in the middle of the month. The diameter of the minor axis of the ring system is about 8". At 22h on September 15, Arcturus is setting in the north-west ; Aldebaran is rising in the north-east, preceded by the beautiful cluster of the Pleiades.

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    The Night Sky in September. Nature 142, 391 (1938).

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