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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

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

 DateRight AscensionDeclinationMag.SizeIllum. (%)Distance (AU)Constellation
Sun5th Sep 201210h 56m 43.4s06d 44m 15.0s-26.731.7'1001.008Leo
Sun15th Sep 201211h 32m 40.1s02d 57m 00.8s-26.731.8'1001.006Leo
Sun25th Sep 201212h 08m 33.8s-00d 55m 46.2s-26.731.9'1001.003Virgo
Mercury5th Sep 201210h 39m 47.5s10d 22m 38.6s-1.605.1"981.329Leo
Mercury15th Sep 201211h 49m 08.9s02d 37m 55.7s-1.404.8"991.393Virgo
Mercury25th Sep 201212h 50m 54.1s-05d 06m 05.2s-0.604.9"951.380Virgo
Venus5th Sep 201208h 00m 01.7s18d 50m 38.2s-4.319.3"600.867Cancer
Venus15th Sep 201208h 45m 28.1s17d 03m 55.0s-4.217.7"650.941Cancer
Venus25th Sep 201209h 31m 09.0s14d 29m 03.9s-4.116.5"691.014Leo
Mars5th Sep 201214h 21m 51.5s-14d 43m 06.5s1.205.1"921.823Virgo
Mars15th Sep 201214h 48m 05.4s-16d 53m 22.5s1.205.0"921.872Libra
Mars25th Sep 201215h 15m 32.2s-18d 53m 13.8s1.204.9"931.916Libra
Jupiter5th Sep 201204h 55m 10.0s21d 47m 47.4s-2.439.7"994.964Taurus
Jupiter15th Sep 201204h 58m 30.4s21d 52m 19.4s-2.441.0"994.812Taurus
Jupiter25th Sep 201205h 00m 32.7s21d 54m 45.7s-2.542.3"994.663Taurus
Saturn5th Sep 201213h 42m 10.8s-08d 07m 16.6s0.915.9"10010.463Virgo
Saturn15th Sep 201213h 46m 00.4s-08d 30m 34.2s0.815.7"10010.569Virgo
Saturn25th Sep 201213h 50m 07.3s-08d 54m 56.5s0.815.6"10010.654Virgo
Uranus5th Sep 201200h 28m 42.2s02d 17m 02.1s5.703.7"10019.143Cetus
Uranus15th Sep 201200h 27m 20.5s02d 08m 09.5s5.703.7"10019.089Cetus
Uranus25th Sep 201200h 25m 53.4s01d 58m 46.4s5.703.7"10019.063Pisces
Neptune5th Sep 201222h 14m 43.4s-11d 32m 43.7s7.802.4"10029.006Aquarius
Neptune15th Sep 201222h 13m 44.0s-11d 38m 18.9s7.802.4"10029.056Aquarius
Neptune25th Sep 201222h 12m 49.6s-11d 43m 23.2s7.802.3"10029.133Aquarius