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.
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.
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.
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.
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.
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 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 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
| ||Date||Right Ascension||Declination||Mag.||Size||Illum. (%)||Distance (AU)||Constellation|
|Sun||5th July 2012||06h 58m 09.4s||22d 45m 40.2s||-26.7||31.5'||100||1.017||Gemini|
|Sun||15th July 2012||07h 38m 58.0s||21d 29m 13.7s||-26.7||31.5'||100||1.016||Gemini|
|Sun||25th July 2012||08h 18m 57.6s||19d 36m 16.2s||-26.7||31.5'||100||1.016||Cancer|
|Mercury||5th July 2012||08h 43m 46.2s||17d 26m 20.9s||0.7||08.7"||34||0.770||Cancer|
|Mercury||15th July 2012||08h 56m 29.6s||14d 07m 01.2s||1.8||10.5"||16||0.644||Cancer|
|Mercury||25th July 2012||08h 39m 57.2s||13d 21m 38.1s||4.5||11.5"||03||0.585||Cancer|
|Venus||5th July 2012||04h 29m 53.0s||17d 23m 02.8s||-4.5||41.9"||20||0.398||Taurus|
|Venus||15th July 2012||04h 46m 56.8s||17d 42m 53.3s||-4.5||35.8"||29||0.467||Taurus|
|Venus||25th July 2012||05h 13m 28.5s||18d 32m 46.2s||-4.4||30.8"||37||0.541||Taurus|
|Mars||5th July 2012||12h 03m 24.5s||00d 00m 19.4s||0.9||06.5"||89||1.446||Virgo|
|Mars||15th July 2012||12h 23m 04.4s||-02d 19m 01.4s||1.0||06.2"||89||1.516||Virgo|
|Mars||25th July 2012||12h 43m 46.1s||-04d 42m 25.0s||1.0||05.9"||90||1.583||Virgo|
|Jupiter||5th July 2012||04h 13m 15.9s||20d 23m 29.0s||-2.1||34.2"||100||5.770||Taurus|
|Jupiter||15th July 2012||04h 21m 48.4s||20d 44m 22.9s||-2.1||34.8"||99||5.670||Taurus|
|Jupiter||25th July 2012||04h 29m 50.0s||21d 02m 20.0s||-2.1||35.5"||99||5.555||Taurus|
|Saturn||5th July 2012||13h 28m 18.1s||-06d 31m 36.9s||0.7||17.4"||100||9.526||Virgo|
|Saturn||15th July 2012||13h 29m 08.2s||-06d 39m 22.8s||0.8||17.1"||100||9.691||Virgo|
|Saturn||25th July 2012||13h 30m 34.1s||-06d 50m 33.3s||0.8||16.9"||100||9.857||Virgo|
|Uranus||5th July 2012||00h 32m 25.1s||02d 42m 40.5s||5.8||03.5"||100||19.955||Cetus|
|Uranus||15th July 2012||00h 32m 31.7s||02d 43m 01.3s||5.8||03.6"||100||19.790||Cetus|
|Uranus||25th July 2012||00h 32m 20.4s||02d 41m 28.5s||5.8||03.6"||100||19.632||Cetus|
|Neptune||5th July 2012||22h 20m 20.3s||-10d 59m 49.8s||7.9||02.3"||100||29.327||Aquarius|
|Neptune||15th July 2012||22h 19m 41.3s||-11d 03m 48.5s||7.8||02.3"||100||29.208||Aquarius|
|Neptune||25th July 2012||22h 18m 53.6s||-11d 08m 34.1s||7.8||02.3"||100||29.112||Aquarius|