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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.

From the southern Hemipshere and tropics, Mercury is an evening object after the first week of September (image from the NASA Messenger space probe)


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).


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

Jupiter and Mars during September 2013 - pdf format


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, 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, 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

Uranus Finder Chart for September 2013 - pdf format


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

Neptune Finder Chart for September 2013 - pdf format

Solar System Data Table September 2013

 DateRight AscensionDeclinationApparent MagnitudeApparent SizeIllum. (%)Distance from Earth (AU)Constellation
Sun5th Sep 201310h 55m 08.7s06d 54m 06.4s-26.731.7'1001.008Leo
Sun15th Sep 201311h 31m 06.4s03d 07m 13.0s-26.731.8'1001.006Leo
Sun25th Sep 201312h 06m 58.8s00d 45m 23.0s-26.731.9'1001.003Virgo
Mercury5th Sep 201311h 33m 58.9s03d 59m 26.0s-0.804.9"951.366Leo
Mercury15th Sep 201312h 33m 09.0s-03d 37m 11.8s-0.305.1"881.308Virgo
Mercury25th Sep 201313h 26m 09.7s-10d 27m 22.3s-0.105.6"801.209Virgo
Venus5th Sep 201313h 22m 50.9s-09d 06m 39.8s-4.115.2"721.096Virgo
Venus15th Sep 201314h 06m 03.2s-13d 51m 31.9s-4.116.3"691.024Virgo
Venus25th Sep 201314h 50m 13.3s-18d 07m 33.4s-4.217.6"650.950Libra
Mars5th Sep 201308h 29m 52.1s20d 03m 14.1s1.704.1"962.275Cancer
Mars15th Sep 201308h 55m 45.3s18d 30m 32.6s1.604.2"962.226Cancer
Mars25th Sep 201309h 20m 49.4s16d 47m 11.8s1.604.3"952.172Cancer
Jupiter5th Sep 201307h 02m 51.5s22d 32m 09.7s-2.135.1"995.613Gemini
Jupiter15th Sep 201307h 09m 37.5s22d 22m 22.5s-2.136.0"995.478Gemini
Jupiter25th Sep 201307h 15m 30.6s22d 13m 08.0s-2.237.0"995.333Gemini
Saturn5th Sep 201314h 22m 44.1s-11d 49m 48.7s0.716.0"10010.399Libra
Saturn15th Sep 201314h 26m 11.0s-12d 08m 56.0s0.715.8"10010.527Libra
Saturn25th Sep 201314h 30m 00.2s-12d 29m 22.4s0.715.6"10010.637Libra
Uranus5th Sep 201300h 43m 08.4s03d 50m 58.1s5.703.7"10019.155Pisces
Uranus15th Sep 201300h 41m 49.3s03d 42m 28.5s5.703.7"10019.088Pisces
Uranus25th Sep 201300h 40m 23.6s03d 33m 19.3s5.703.7"10019.049Pisces
Neptune5th Sep 201322h 22m 46.1s-10d 51m 22.0s7.802.4"10028.986Aquarius
Neptune15th Sep 201322h 21m 46.0s-10d 57m 08.4s7.802.4"10029.029Aquarius
Neptune25th Sep 201322h 20m 50.4s-11d 02m 26.4s7.802.3"10029.100Aquarius