Mercury
Mercury has recently passed through superior conjunction (August 24th) and becomes visible in evening sky after the first week of September for those located in the tropics and southern hemisphere. The planet appears low down above the western horizon just after sunset and remains observable until the third week of October. Indeed, this is the most favourable evening apparition of the year for those concerned.
On September 10th from latitudes of 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury is 8 degrees above the horizon, 30 minutes after sunset. With a magnitude of -0.5, it will be easy to spot with binoculars and also visible to the naked eye. Mercury then climbs a little higher in the sky each subsequent evening; although at the same time its brightness gradually fades. Peak altitude occurs on October 9th, the date of greatest eastern elongation, when the planet will be 20 degrees above the horizon and shine at mag. -0.1.
On September 24th, Mercury (mag. -0.1) passes 0.8 degrees north of Spica (α Vir) the brightest star in Virgo (mag. +1.0).
Unfortunately, from northern temperate latitudes during September, Mercury remains unsuitably placed for observation.
Venus
Throughout September, Venus remains a spectacular "evening star" for observers located at southern and equatorial latitudes; an unmistakable blazing beacon shining above the western horizon. The visibility continues to improve as the month progresses. On September 1st, the planet sets about 3 hours after the Sun, increasing to nearly 4 hours by months end. Just as with Mercury, northern hemisphere observers are not so fortunate. Venus is visible towards the west-southwest horizon at dusk, but remains inconveniently low, setting just over 1 hour after the Sun.
The magnitude of Venus improves from -4.0 to -4.2 with the illuminated phase of the planet decreasing from 74 percent to 63 percent during September. On the 18th, Venus crosses into Libra from Virgo, where it remains for the remainder of the month.
On September 8th, the waxing crescent Moon passes 0.4 degrees south of Venus and an occultation is visible from southern South America and French Polynesia. Later in the month (Sep 20th), Venus passes 4 degrees south of much fainter Saturn (mag. +0.7).
Mars
Fast moving Mars is currently an early morning object. The intriguing "Red planet" is visible for a couple of hours in the eastern sky before sunrise for those located in the northern hemisphere, but rather less favourably placed for those living further south.
To the naked eye Mars (mag. +1.6) appears red-orange in colour. Its apparent size is slowly increasing but remains less than 4.5 arc seconds; spotting any details telescopically is very difficult.
On September 2nd, the thin 9% illuminated waning crescent Moon passes 6 degrees south of Mars and between September 7th and the 10th, Mars passes through the southern part of bright sprawling open cluster M44 "The Praesepe".
Jupiter and Mars during September 2013 - pdf format
Jupiter
Jupiter is now a brilliant object in Gemini, brightening from mag. -2.0 to -2.2 during September. The planet continues to move direct amongst the stars of Gemini and by the end of the month rises shortly before midnight from northern temperate latitudes, although not until 3 hours later from the southern hemisphere. The apparent size of Jupiter increases from 35 to 38 arc seconds during September, allowing ever more detail to be seen through telescopes.
On September 28th, the waning last-quarter Moon passes 5 degrees south of Jupiter in the morning sky.
Saturn
Saturn, mag. +0.7, continues to remain visible as an early evening object towards the west-southwest throughout September. However, its period of visibility is now fast diminishing and from northern temperate latitudes the "Ringed" planet will be rather low in the twilight at dusk by months end, although a somewhat easier object for observers located further south.
On September 1st, Saturn moves into Libra from Virgo where it remains for the rest of the month. The 18% illuminated waxing crescent Moon passes 2 degrees south of Saturn on September 9th with the much brighter Venus (mag. -4.2) passing 4 degrees south of Saturn on the 20th of the month.
Uranus
Uranus, magnitude +5.7, is now an evening object amongst the stars of Pisces. At the start of the month, the distant planet rises in the east less than two hours or so after sunset and continues to rise a little earlier each day as the month progresses. It then remains visible for the remainder of the night.
Uranus is visible to the naked eye from a dark site, but if you can't spot it, binoculars or a small telescope make the task easier. On September 20th, the full Moon passes 3 degrees north of Uranus.
Uranus Finder Chart for September 2013 - pdf format
Neptune
Neptune (mag. +7.8), is located in Aquarius and has just past opposition (August 27th). During September, the planet is visible as soon as its dark enough until just before sunrise.
With a declination of -10 degrees, Neptune is currently situated better for observation for observers located in either the tropics or southern hemisphere than for those in the northern hemisphere and is positioned about 1 degree to the west of Sigma (σ) Aquarii mag. +4.8.
On September 17th, the almost full Moon passes 6 degrees north of Neptune.
Neptune Finder Chart for September 2013 - pdf format
Solar System Data Table September 2013
| Date | Right Ascension | Declination | Apparent Magnitude | Apparent Size | Illum. (%) | Distance from Earth (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th Sep 2013 | 10h 55m 08.7s | 06d 54m 06.4s | -26.7 | 31.7' | 100 | 1.008 | Leo |
| Sun | 15th Sep 2013 | 11h 31m 06.4s | 03d 07m 13.0s | -26.7 | 31.8' | 100 | 1.006 | Leo |
| Sun | 25th Sep 2013 | 12h 06m 58.8s | 00d 45m 23.0s | -26.7 | 31.9' | 100 | 1.003 | Virgo |
| Mercury | 5th Sep 2013 | 11h 33m 58.9s | 03d 59m 26.0s | -0.8 | 04.9" | 95 | 1.366 | Leo |
| Mercury | 15th Sep 2013 | 12h 33m 09.0s | -03d 37m 11.8s | -0.3 | 05.1" | 88 | 1.308 | Virgo |
| Mercury | 25th Sep 2013 | 13h 26m 09.7s | -10d 27m 22.3s | -0.1 | 05.6" | 80 | 1.209 | Virgo |
| Venus | 5th Sep 2013 | 13h 22m 50.9s | -09d 06m 39.8s | -4.1 | 15.2" | 72 | 1.096 | Virgo |
| Venus | 15th Sep 2013 | 14h 06m 03.2s | -13d 51m 31.9s | -4.1 | 16.3" | 69 | 1.024 | Virgo |
| Venus | 25th Sep 2013 | 14h 50m 13.3s | -18d 07m 33.4s | -4.2 | 17.6" | 65 | 0.950 | Libra |
| Mars | 5th Sep 2013 | 08h 29m 52.1s | 20d 03m 14.1s | 1.7 | 04.1" | 96 | 2.275 | Cancer |
| Mars | 15th Sep 2013 | 08h 55m 45.3s | 18d 30m 32.6s | 1.6 | 04.2" | 96 | 2.226 | Cancer |
| Mars | 25th Sep 2013 | 09h 20m 49.4s | 16d 47m 11.8s | 1.6 | 04.3" | 95 | 2.172 | Cancer |
| Jupiter | 5th Sep 2013 | 07h 02m 51.5s | 22d 32m 09.7s | -2.1 | 35.1" | 99 | 5.613 | Gemini |
| Jupiter | 15th Sep 2013 | 07h 09m 37.5s | 22d 22m 22.5s | -2.1 | 36.0" | 99 | 5.478 | Gemini |
| Jupiter | 25th Sep 2013 | 07h 15m 30.6s | 22d 13m 08.0s | -2.2 | 37.0" | 99 | 5.333 | Gemini |
| Saturn | 5th Sep 2013 | 14h 22m 44.1s | -11d 49m 48.7s | 0.7 | 16.0" | 100 | 10.399 | Libra |
| Saturn | 15th Sep 2013 | 14h 26m 11.0s | -12d 08m 56.0s | 0.7 | 15.8" | 100 | 10.527 | Libra |
| Saturn | 25th Sep 2013 | 14h 30m 00.2s | -12d 29m 22.4s | 0.7 | 15.6" | 100 | 10.637 | Libra |
| Uranus | 5th Sep 2013 | 00h 43m 08.4s | 03d 50m 58.1s | 5.7 | 03.7" | 100 | 19.155 | Pisces |
| Uranus | 15th Sep 2013 | 00h 41m 49.3s | 03d 42m 28.5s | 5.7 | 03.7" | 100 | 19.088 | Pisces |
| Uranus | 25th Sep 2013 | 00h 40m 23.6s | 03d 33m 19.3s | 5.7 | 03.7" | 100 | 19.049 | Pisces |
| Neptune | 5th Sep 2013 | 22h 22m 46.1s | -10d 51m 22.0s | 7.8 | 02.4" | 100 | 28.986 | Aquarius |
| Neptune | 15th Sep 2013 | 22h 21m 46.0s | -10d 57m 08.4s | 7.8 | 02.4" | 100 | 29.029 | Aquarius |
| Neptune | 25th Sep 2013 | 22h 20m 50.4s | -11d 02m 26.4s | 7.8 | 02.3" | 100 | 29.100 | Aquarius |