The moon begins this month at full phase. A few days later, Sept. 5, the moon occults Mars for viewers in the Southern Hemisphere – a very close conjunction for Northern Hemisphere observers. Sept. 11, the third-quarter Luna skirts less than half a degree south of the cluster, M35, in the eastern morning sky for early risers. On the morning of Sept. 13, Venus is four degrees south of the moon. By Sept. 25, Jupiter is 1.4 degrees north of the first-quarter moon, while a little later, Saturn is three degrees north. Jupiter and Saturn are gradually closing up the gap that will culminate on a closest approach on Dec. 21. Neptune and Uranus are visited by the moon Sept. 2 and 7, respectively.
Mercury gradually moves away from the sun in what will be its greatest elongation east (GEE) in the western evening sky. Unfortunately, the angle of the ecliptic makes this an unfavourable apparition for northern observers, so Mercury hugs the horizon right at sundown – a tough observation. On the early morning of Sept. 21, the speedy planet is 0.3 degrees above the bright star, Spica, in the constellation Virgo (the Maiden).
Venus commands the morning sky well above the horizon, shining like a beacon before sunrise and often described as a UFO by the unknowing. The waning crescent moon passes by Sept. 13.
Mars is in its best apparition of the 2020s, rising at sunset and setting at dawn. The moon joins up with the Red Planet Sept. evenings of Sept. 5 and 6, an occultation in South America. Mars appears to become stationary Sept. 9 and thereafter begins retrograde motion – apparently moving westward. This strange behaviour greatly puzzled the ancient astronomers, resulting in all sorts of weird ideas. What they failed to take into account was the Earth’s own motion, more rapid than Mars, so we overtake it during an opposition. It was Copernicus and Galileo who put forth the idea that the sun, not the Earth, was at the centre of the Solar System.
Jupiter has been retrograding and becomes stationary Sept. 13 beginning prograde motion against the background stars of Sagittarius. Watch for the moon passing by Sept. 25.
Saturn has also been retrograding, and begins prograde motion Sept. 29. The moon catches up with the Ringed Planet Sept. 25, only two degrees south.
Uranus rises before midnight. On the night of Sept. 7, the moon is directly south of the blue-green gas planet with the Pleiades and Hyades clusters off to the east.
Neptune rises about 8 p.m., and the moon joins up on the evening of Sept. 2.
The Autumn equinox occurs on Sept. 22 at 1:31 UT (early in the morning in North America).
The zodiacal light is visible in the east before sunrise for the last two weeks of the month.
James Edgar has had an interest in the night sky all his life. He joined The Royal Astronomical Society of Canada in 2000, was national president for two terms, is now the editor of the Observer’s Handbook, and production manager of the bi-monthly RASC Journal. The IAU named asteroid 1995 XC5 “(22421) Jamesedgar” in his honour.
