Mercury
Unfortunately, Mercury is not well placed for observation this month. From our perspective, the planet is currently moving behind the Sun and will reach superior conjunction on September 10th. As a result, for most of September it appears too close to the Sun to be safely observed. At conjunction, Mercury will be located a distant 1.37 AU or 205 million km (127 million miles) from Earth.
The exception is during the last week of September when for southern hemisphere observers Mercury will set about 75 minutes after the Sun. However, the planet is located low down towards the western horizon and at magnitude -0.5 is likely to be difficult to spot in the bright early sunset sky.
Venus
Venus remains a brilliant unmistakable object in the early morning sky during September. From northern hemisphere temperate latitudes the planet rises a full 4 hours before the Sun. For observers located in equatorial and southern hemisphere locations the visibility period is not quite as long, but still a respectable 2 hours or more.
The planet starts the month in Gemini and is positioned almost half way along an imaginary line between Gemini’s brightest star Pollux (mag. 1.1) and Procyon (mag 0.3), the brightest star in Canis Minor. Of course, Venus is much the brighter of the three; nearly 75x brighter than Procyon and almost 150x brighter than Pollux. Venus continues its rapid eastward motion, arriving in Cancer on September 4th. It then moves swiftly through Cancer before crossing the border into Leo on September 23rd.
During the month Venus fades slightly from magnitude -4.3 to -4.1, while the lit phase of the planet increasing from 58% to 70%. On September 12th, the thin crescent Moon will pass only 4 degrees south of Venus.
Mars
Mars at magnitude 1.2 continues to be visible in the early evening sky but now sets less than two hours after the Sun. However, the planets rapid eastward motion means that the time at which it sets after the Sun will only change by about 10 minutes during September.
The red planet starts the month in Virgo about 10 degrees east of Saturn before crossing the border into Libra on September 5, where it spends the remainder of the month moving through the constellation. On September 19, the 11 percent lit crescent Moon will pass only 0.2 degrees south of Mars and an occultation is visible from central South America and French Polynesia.
Jupiter
Jupiter remains a brilliant morning object and continues to rise earlier during September. For northern hemisphere observers the giant planet rises around midnight on September 1st and around mid-evening by months end. It’s not quite so good from southern latitudes with Jupiter rising a couple of hours or so later than their northern counterparts.
For the whole of September, the gas giant remains in Taurus and is located a few degrees northeast of Aldebaran (mag. 0.9) and about 20 degrees southeast of the famous Pleiades star cluster (M45). It also increases in both magnitude and apparent size this month; the mag. improves from -2.3 to -2.5 with the apparent diameter increasing from 39 to 43 arc seconds.
On September 8, the last quarter Moon will pass 0.6 degrees south of Jupiter. An occultation is visible from the South Pacific Ocean to the west of South America.
Jupiter in Taurus during September 2012 - pdf format
Saturn
Saturn at magnitude 0.9 is located in Virgo and may be glimpsed during the first half of the month, low down towards the western horizon as darkness falls. For northern hemisphere observers come the second half of the month, Saturn will be battling against the bright evening twilight. It will be increasing more difficult to see before it is eventually lost to the Sun’s glare. Those living in the tropics and southern hemisphere should be able to track Saturn for a little time longer. On September 30th, when viewed from Sydney Australia the planet will be positioned about 8° above the western horizon one hour after sunset.
Saturn is located about 6 degrees to the northeast of mag. 1.0 star Spica and on September 18th, the 6% lit crescent Moon will pass 5 degrees to the south of the Saturn.
Uranus
Uranus reaches opposition on September 29th in Pisces and is visible all night. At magnitude 5.7, the planet is faintly visible to the naked eye under dark skies and good conditions. Even if you can’t see Uranus with the naked eye it is a very easy binocular target.
At opposition, Uranus is located approx. 19.061 AU or 2851.5 million km (1771.8 million miles) from Earth. It has an apparent diameter of 3.7 arc seconds and with sufficiently high magnification even small telescopes will show the planets disk. However, it is a featureless world even when viewed through the largest amateur telescopes.
Uranus is located close to star 44 Piscium, which at mag. 5.8 is almost equal in brightness.
Neptune
Neptune has only just passed opposition for this year (on August 24) and hence is still visible for most of the night. It is located in the constellation of Aquarius and located only four degrees south of mag. 4.2 star Ancha (theta Aquarii). At mag. 7.8, Neptune is not a naked eye target but is visible with binoculars.
Solar System Data September 2012
| Date | Right Ascension | Declination | Mag. | Size | Illum. (%) | Distance (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th Sep 2012 | 10h 56m 43.4s | 06d 44m 15.0s | -26.7 | 31.7' | 100 | 1.008 | Leo |
| Sun | 15th Sep 2012 | 11h 32m 40.1s | 02d 57m 00.8s | -26.7 | 31.8' | 100 | 1.006 | Leo |
| Sun | 25th Sep 2012 | 12h 08m 33.8s | -00d 55m 46.2s | -26.7 | 31.9' | 100 | 1.003 | Virgo |
| Mercury | 5th Sep 2012 | 10h 39m 47.5s | 10d 22m 38.6s | -1.6 | 05.1" | 98 | 1.329 | Leo |
| Mercury | 15th Sep 2012 | 11h 49m 08.9s | 02d 37m 55.7s | -1.4 | 04.8" | 99 | 1.393 | Virgo |
| Mercury | 25th Sep 2012 | 12h 50m 54.1s | -05d 06m 05.2s | -0.6 | 04.9" | 95 | 1.380 | Virgo |
| Venus | 5th Sep 2012 | 08h 00m 01.7s | 18d 50m 38.2s | -4.3 | 19.3" | 60 | 0.867 | Cancer |
| Venus | 15th Sep 2012 | 08h 45m 28.1s | 17d 03m 55.0s | -4.2 | 17.7" | 65 | 0.941 | Cancer |
| Venus | 25th Sep 2012 | 09h 31m 09.0s | 14d 29m 03.9s | -4.1 | 16.5" | 69 | 1.014 | Leo |
| Mars | 5th Sep 2012 | 14h 21m 51.5s | -14d 43m 06.5s | 1.2 | 05.1" | 92 | 1.823 | Virgo |
| Mars | 15th Sep 2012 | 14h 48m 05.4s | -16d 53m 22.5s | 1.2 | 05.0" | 92 | 1.872 | Libra |
| Mars | 25th Sep 2012 | 15h 15m 32.2s | -18d 53m 13.8s | 1.2 | 04.9" | 93 | 1.916 | Libra |
| Jupiter | 5th Sep 2012 | 04h 55m 10.0s | 21d 47m 47.4s | -2.4 | 39.7" | 99 | 4.964 | Taurus |
| Jupiter | 15th Sep 2012 | 04h 58m 30.4s | 21d 52m 19.4s | -2.4 | 41.0" | 99 | 4.812 | Taurus |
| Jupiter | 25th Sep 2012 | 05h 00m 32.7s | 21d 54m 45.7s | -2.5 | 42.3" | 99 | 4.663 | Taurus |
| Saturn | 5th Sep 2012 | 13h 42m 10.8s | -08d 07m 16.6s | 0.9 | 15.9" | 100 | 10.463 | Virgo |
| Saturn | 15th Sep 2012 | 13h 46m 00.4s | -08d 30m 34.2s | 0.8 | 15.7" | 100 | 10.569 | Virgo |
| Saturn | 25th Sep 2012 | 13h 50m 07.3s | -08d 54m 56.5s | 0.8 | 15.6" | 100 | 10.654 | Virgo |
| Uranus | 5th Sep 2012 | 00h 28m 42.2s | 02d 17m 02.1s | 5.7 | 03.7" | 100 | 19.143 | Cetus |
| Uranus | 15th Sep 2012 | 00h 27m 20.5s | 02d 08m 09.5s | 5.7 | 03.7" | 100 | 19.089 | Cetus |
| Uranus | 25th Sep 2012 | 00h 25m 53.4s | 01d 58m 46.4s | 5.7 | 03.7" | 100 | 19.063 | Pisces |
| Neptune | 5th Sep 2012 | 22h 14m 43.4s | -11d 32m 43.7s | 7.8 | 02.4" | 100 | 29.006 | Aquarius |
| Neptune | 15th Sep 2012 | 22h 13m 44.0s | -11d 38m 18.9s | 7.8 | 02.4" | 100 | 29.056 | Aquarius |
| Neptune | 25th Sep 2012 | 22h 12m 49.6s | -11d 43m 23.2s | 7.8 | 02.3" | 100 | 29.133 | Aquarius |