Mercury has its worst evening apparition of the year for observers in the Northern Hemisphere. It reaches greatest eastern elongation from the Sun - 26° - on September 21. However, the ecliptic lies at such a shallow angle to the horizon that Mercury is only 7° above the horizon at sunset, and 3° high a half hour later when the sky might be dark enough to spot it. It retains this altitude for several days before and after this date. Mercury is actually quite bright at magnitude 0.0, so it might be easy to spot in binoculars in spite of its low altitude.
Saturn is getting increasingly low in the western sky after sunset. On Sept. 1st, the planet lies 24° above the western horizon a half hour after sunset; by the 30th, its altitude is just 13° at 30 minutes after sunset. At midmonth its disk spans 16 arc-seconds, while its rings stretch 37", and are tilted 23° to our line of sight. This month represents the last opportunity to get good views of Saturn, so take advantage of it! When will Saturn return? Please check our "What's New" page to find out!
On September 1, Mars lies just 5° to the right of Saturn, but the gap widens as Mars moves eastward. On the 27th, Mars passes just 3° to the south of its similarly colored rival, Antares. (The star's name can be translated as "rival of Ares" - the Greek name for Mars). The view of Mars through a telescope is disappointing, as it is only about 6" across - far too small to reveal any surface detail.
Neptune reached opposition on August 29, which means it was at its closest, brightest, and largest of this entire year. Throughout September, it remains a prime viewing target. At magnitude 7.8, the planet is well below naked-eye visibility, though it can easily be picked up in binoculars if you know where to look. In a telescope, it shows a tiny blue-grey disk about 2.4" across.
Our Solar System's other "ice giant,"Uranus, follows Neptune across the night sky. It rises about an hour and a half after Neptune, in the constellation Pisces. It will not reach opposition until early October, but it is already near its peak magnitude of 5.7 (bright enough, incidentally, to be seen with the naked eye under good conditions). In a telescope, it displays a clear greyish-green disk about 3.7" wide.
Jupiter rises two and a half hours before the Sun as September begins, and four and a half hours before sunrise by month's end. It shines at magnitude -1.8, and is increasingly easy to see as it climbs higher day by day. In a telescope, it displays a disk 33" across, large enough to show detail even when the planet is low. Its four large moons - Io, Europa, Ganymede, and Callisto - are visible even in small telescopes, and you can follow their changing patterns night by night.
As September begins, Venus rises about an hour and a quarter before the Sun, and lies about 15° to Jupiter's lower left. Its brightness, magnitude -3.9, makes it hard to miss even in the morning twilight. As the month goes on, however, it rises later and later; by the 30th, it is virtually lost in the solar glare.
At midmonth, the dwarf planet/asteroid 1 Ceres is about 5.5° to the upper right of Saturn.
Pluto lies due north of the "Teapot" in Sagittarius; It shines no brighter than magnitude 14.1, and represents a difficult target in this crowded region of the sky.