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Mercury

Mercury reaches greatest eastern elongation on July 1. On this date, the separation is a good 26 degrees but unfortunately for northern hemisphere observers the angle is not favourable; the planet appears low down after sunset and unlikely to be seen in the evening twilight. Observers in the southern hemisphere and tropics fare much better. Here Mercury is visible during the first two weeks of the month towards the WNW horizon. The chart below shows how the altitude of Mercury varies during June and July when viewed from Sydney, Australia (34S) one hour after sunset. For people located at similar latitudes to Sydney, a comparable view occurs.

Mercury during June and July 2012

Mercury during June and July 2012 from Sydney, Australia - pdf format

During the period of visibility, Mercury fades from mag. 0.4 on July 1 to mag. 2.0 on July 16. The planet's elongation from the Sun then rapidly decreases as it moves towards inferior conjunction on July 28.

Venus

Following on from last month's spectacular transit of the Sun, Venus is now visible as a morning object among the stars of Taurus. During the first half of the month, Venus rises over two hours before the Sun for observers in the southern hemisphere and tropics, although still low down in the morning twilight for northern hemisphere observers. By months end, Venus is much better placed for all, rising at least 3 hours before the Sun. The mag. of Venus during July is about -4.5 with the apparent disk size decreasing from 45 to 28 arc seconds as the month progresses.

On July 15, there is a superb photographic opportunity when Venus appears close to Jupiter, the crescent Moon and first mag. star Aldebaran in the pre dawn sky.

Moon, Venus, Jupiter and Aldebaran as seen on July 15, 2012

Moon, Venus, Jupiter and Aldebaran as seen on July 15, 2012 - pdf format

Mars

Mars is now moving direct in Virgo and is visible as soon as it gets dark. The planet is now a few months past opposition and past its best. The brightness of the red planet changes little during the month, decreasing from mag. 0.9 to 1.0. During this time, the apparent size also varies little at around 6 arc seconds.

The planets eastwards motion is so fast that by months end the gap between Mars and Saturn is noticeably less than at the start of the month.

Saturn and Mars in Virgo - July 2012

Saturn and Mars in Virgo - July 2012 - pdf format

Jupiter

Jupiter is now a morning object in Taurus. The great planet is now moving closer to Earth and will continue to increase in brightness and apparent size until it reaches opposition in December. Currently shining at mag. -2.1, Jupiter is well placed at the beginning of the month for observers in the southern hemisphere and tropics, rising more than 2 hours before sunrise. For northern hemisphere observers, Jupiter at this time remains quite low in the morning twilight but by the middle and the end of the month the planet is more conspicuous.

On July 15, the Moon occults Jupiter and its four largest moons. This rare event is visible from Europe and North Africa. Venus and first mag. star Aldebaran are located close by.

Saturn

Like Mars, Saturn is visible as soon darkness falls. Also like Mars, Saturn is now past opposition and past its best for this year but still shines at mag. 0.8 with a respectable apparent disk size of 17 arc seconds. The planet sets before midnight at the end of the month and is easy to find; it is located just a few degrees north of mag. 1.0 star Spica. Mars is also in Virgo to the west of Saturn but rapidly closing the gap between the two.

Uranus

Uranus is now well placed in the morning sky, rising before midnight. The seventh planet from the Sun shines at mag. 5.8 in the northwest part of the constellation of Cetus. It is about 1.5 east of almost equal brightness star, 44 Piscium (mag. 5.8).

Neptune

Neptune is also well placed in the morning sky. Located in Aquarius, it shines at mag. 7.8 and now rises before midnight. The planet is a relatively easy binocular object, located three degrees south of mag. 4.2 star Ancha (theta Aquarii).

Solar System Data Table July 2012

 DateRight AscensionDeclinationMag.SizeIllum. (%)Distance (AU)Constellation
Sun5th July 201206h 58m 09.4s22d 45m 40.2s-26.731.5'1001.017Gemini
Sun15th July 201207h 38m 58.0s21d 29m 13.7s-26.731.5'1001.016Gemini
Sun25th July 201208h 18m 57.6s19d 36m 16.2s-26.731.5'1001.016Cancer
Mercury5th July 201208h 43m 46.2s17d 26m 20.9s0.708.7"340.770Cancer
Mercury15th July 201208h 56m 29.6s14d 07m 01.2s1.810.5"160.644Cancer
Mercury25th July 201208h 39m 57.2s13d 21m 38.1s4.511.5"030.585Cancer
Venus5th July 201204h 29m 53.0s17d 23m 02.8s-4.541.9"200.398Taurus
Venus15th July 201204h 46m 56.8s17d 42m 53.3s-4.535.8"290.467Taurus
Venus25th July 201205h 13m 28.5s18d 32m 46.2s-4.430.8"370.541Taurus
Mars5th July 201212h 03m 24.5s00d 00m 19.4s0.906.5"891.446Virgo
Mars15th July 201212h 23m 04.4s-02d 19m 01.4s1.006.2"891.516Virgo
Mars25th July 201212h 43m 46.1s-04d 42m 25.0s1.005.9"901.583Virgo
Jupiter5th July 201204h 13m 15.9s20d 23m 29.0s-2.134.2"1005.770Taurus
Jupiter15th July 201204h 21m 48.4s20d 44m 22.9s-2.134.8"995.670Taurus
Jupiter25th July 201204h 29m 50.0s21d 02m 20.0s-2.135.5"995.555Taurus
Saturn5th July 201213h 28m 18.1s-06d 31m 36.9s0.717.4"1009.526Virgo
Saturn15th July 201213h 29m 08.2s-06d 39m 22.8s0.817.1"1009.691Virgo
Saturn25th July 201213h 30m 34.1s-06d 50m 33.3s0.816.9"1009.857Virgo
Uranus5th July 201200h 32m 25.1s02d 42m 40.5s5.803.5"10019.955Cetus
Uranus15th July 201200h 32m 31.7s02d 43m 01.3s5.803.6"10019.790Cetus
Uranus25th July 201200h 32m 20.4s02d 41m 28.5s5.803.6"10019.632Cetus
Neptune5th July 201222h 20m 20.3s-10d 59m 49.8s7.902.3"10029.327Aquarius
Neptune15th July 201222h 19m 41.3s-11d 03m 48.5s7.802.3"10029.208Aquarius
Neptune25th July 201222h 18m 53.6s-11d 08m 34.1s7.802.3"10029.112Aquarius