When September arrives, the hours of darkness grow longer in the Northern Hemisphere, while day-length decreases. The shorter daylight hours trigger all kinds of biological events, such as animal migrations and fall leaf color changes. The longer nights bring greater opportunities for skywatchers to view the wonders of the night sky. Meanwhile, September 22nd this year will mark the time of the Autumnal Equinox, which occurs at precisely 10:29 pm EDT. This marks the moment when the Sun appears to cross the Celestial Equator, appearing to move below or south of it. Earth’s tilt and its constant annual motion around the Sun cause this each year. This means that we are heading towards winter. Winter’s cold is still months away and September nights are very comfortable for getting outside.
Saturn the beautiful ringed planet stays above our southwestern horizon all month, but it is getting lower each night. In the first week of September it is 20 degrees above the horizon one hour after sunset, with Mars just 5 degrees to its left. Both are down to magnitude 0.6, but Mars appears reddish-orange, while Saturn is more yellowish. By the end of September Saturn will only be 10 degrees above the horizon an hour after sunset, while Mars will appear to move much faster against the background stars all month because it orbits the Sun much faster than Saturn. This motion will take Mars east, or left, of Saturn out of Libra, across Scorpius, and into Ophiuchus. On September 27th, Mars will pass just 3 degrees above Antares, a red star and the brightest star in Scorpius. Saturn will be to the right, or west of Mars that evening, and the waxing crescent Moon will be seen just 0ne degree to the right of Saturn! Two nights later on the 29th, look for the Moon to be directly above the pair of planets.
In the early morning eastern sky we can find Jupiter at magnitude –1.8 rising about 4 am local daylight time in early days of September. During the month it will rise sooner and appear higher above the horizon. Venus may be spotted in early September, rising around 5 am and appearing even closer to the horizon. But with a good clear view to the horizon, we can spot it easily because it is so bright — -3.9 magnitude. By the end of the month it will be only a few degrees from the Sun and be lost to us in its glare.
The Full Moon this month will be on the 8th; Last Quarter on the 15th; and New Moon will be on the 24th.