Mercury reaches greatest elongation east on July 30th, when it moves out to 27.2 degrees from the Sun. From Southern Hemisphere locations, the planet can be seen early in the month low down towards the northwestern horizon just after sunset. Visibility then improves gradually each evening until greatest elongation is reached. For example, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury will be 16 degrees above the horizon, 45 minutes after sunset. From the middle to the end of the month, its magnitude decreases from -0.5 to +0.3.
On July 25th, the thin crescent Moon passes less than a degree north of Mercury and on the following day Mercury passes a degree south of Regulus (mag. +1.4).
From mid-latitude northern temperate locations the planet isn't so well placed, but can be spotted hugging the western horizon near the end of the month.
Venus remains a brilliant morning object. From mid-latitude northern temperate locations the planet's visibility actually improves slightly during July. It rises about 2 hours and 45 minutes before the Sun at the start of month, increasing to about 3 hours by months end. From southern temperate locations, Venus rises up to 3.5 hours before the Sun on July 1st although an hour less by July 31st.
As the month progresses, the planet fades slightly from magnitude -4.2 to -4.0 with its illuminated phase increasing from 63% to 74%. On July 14th, Venus passes 3 degrees north of Aldebaran (mag. +0.9) and on July 20th the waning crescent Moon passes 3 degrees south of the planet.
Mars reaches solar conjunction on July 27th and is therefore unsuitably placed for observation throughout the month.
Although fading, Jupiter remains a brilliant evening object moving direct in Virgo. It's visible towards the west as soon as it's dark enough. However, by months end it sets before midnight from northern temperate latitudes, although slightly earlier for those located further south.
As the month progresses, the giant planet fades from magnitude -2.0 to -1.9 with its apparent size decreasing from 37 to 34 arc seconds. On July 1st, the waxing crescent Moon passes 3 degrees north of Jupiter.
Saturn remains well placed for observation throughout July. The "Ringed" planet is only a month passed opposition and is visible after sunset. It then remains observable for most of the remainder of the night.
Saturn is currently moving slowly retrograde in Ophiuchus close to the border with Sagittarius. With the Earth slowly distancing itself, the apparent brightness and size of the planet continues to decrease. Its magnitude fades from +0.1 to +0.3, with its apparent diameter shrinking from 18.3 to 17.8 arc seconds as the month progresses.
Saturn's wonder of course is its ring system. They are currently wide open and even a small 80mm (3.1-inch) scope will easily show them. Larger telescopes display much detail. For example, a 200mm (8-inch) reflector under good seeing conditions reveals the 0.7 arc seconds wide Cassini division, the Enke division, the hazy C-ring and up to half a dozen satellites.
On July 7th, the waxing gibbous Moon passes 3 degrees north of Saturn.
Uranus, mag. +5.8, is located in Pisces close to the border with Aries. From mid-northern temperate locations at the beginning of the month, it rises 4 hours before the Sun. By months end, it can be seen an hour or so after midnight. For those located further south the visibility period is slightly better still.
Under dark skies Uranus is faintly visible to the naked eye, although from most populated areas optical aid is required. The planet is positioned a degree north of omicron Psc (ο Psc - mag. +4.3).
On July 17th, the last quarter Moon passes 4 degrees south of Uranus.
Neptune continues to move slowly retrograde in Aquarius. With opposition now a month away, the distant planet is now well placed for observation. At the start of July, it rises after midnight from northern temperate latitudes. From further south, it's even better placed and visible up to a couple of hours earlier than that.
Neptune is located 30 degrees south and slightly west of the centre of the Great Square of Pegasus. Lambda Aqr (λ Aqr - mag. +3.7) is positioned 2.5 degrees west-southwest of the planet. Neptune is the only planet that's never bright enough to be spotted with the naked eye. However, it's relatively easy to see with binoculars or small scopes.
Neptune brightens marginally from magnitude +7.9 to +7.8 as the month progresses. On July 13th, the waning gibbous Moon passes a degree south of the planet.
Solar System Data Table July 2017
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||5th Jul 2017||06h 56m 15.0s||22d 48m 27.3s||-26.7||31.5'||100||1.017||Gemini|
|Sun||15th Jul 2017||07h 37m 05.0s||21d 33m 47.9s||-26.7||31.5'||100||1.016||Gemini|
|Sun||25th Jul 2017||08h 17m 07.1s||19d 42m 28.4s||-26.7||31.5'||100||1.016||Cancer|
|Mercury||5th Jul 2017||08h 01m 28.1s||22d 24m 54.1s||-0.8||05.4"||85||1.235||Cancer|
|Mercury||15th Jul 2017||09h 11m 09.4s||17d 27m 05.5s||-0.2||06.1"||69||1.098||Cancer|
|Mercury||25th Jul 2017||10h 02m 37.7s||11d 39m 40.2s||0.1||07.1"||54||0.948||Leo|
|Venus||5th Jul 2017||03h 52m 34.6s||17d 33m 19.0s||-4.2||17.6"||64||0.950||Taurus|
|Venus||15th Jul 2017||04h 38m 26.2s||19d 46m 30.4s||-4.1||16.3"||68||1.025||Taurus|
|Venus||25th Jul 2017||05h 26m 21.6s||21d 17m 52.1s||-4.0||15.2"||72||1.098||Taurus|
|Mars||5th Jul 2017||07h 25m 57.1s||23d 00m 36.3s||+1.7||03.6"||100||2.628||Gemini|
|Mars||15th Jul 2017||07h 53m 40.6s||21d 57m 20.0s||+1.7||03.5"||100||2.644||Gemini|
|Mars||25th Jul 2017||08h 20m 48.8s||20d 37m 51.2s||+1.7||03.5"||100||2.654||Cancer|
|Jupiter||5th Jul 2017||12h 53m 14.2s||-04d 18m 00.1s||-2.0||36.9"||99||5.339||Virgo|
|Jupiter||15th Jul 2017||12h 56m 19.9s||-04d 40m 03.1s||-2.0||35.9"||99||5.494||Virgo|
|Jupiter||25th Jul 2017||13h 00m 19.3s||-05d 07m 24.0s||-1.9||34.9"||99||5.645||Virgo|
|Saturn||5th Jul 2017||17h 29m 12.5s||-21d 55m 34.2s||+0.1||18.3"||100||9.098||Ophiuchus|
|Saturn||15th Jul 2017||17h 26m 30.1s||-21d 54m 50.0s||+0.2||18.1"||100||9.169||Ophiuchus|
|Saturn||25th Jul 2017||17h 24m 13.3s||-21d 54m 28.9s||+0.2||17.9"||100||9.264||Ophiuchus|
|Uranus||5th Jul 2017||01h 44m 37.5s||10d 12m 16.9s||+5.8||03.5"||100||20.161||Pisces|
|Uranus||15th Jul 2017||01h 45m 21.9s||10d 16m 12.7s||+5.8||03.5"||100||19.995||Pisces|
|Uranus||25th Jul 2017||01h 45m 48.4s||10d 18m 26.6s||+5.8||03.6"||100||19.827||Pisces|
|Neptune||5th Jul 2017||23h 02m 11.5s||-07d 09m 52.6s||+7.9||02.3"||100||29.442||Aquarius|
|Neptune||15th Jul 2017||23h 01m 44.7s||-07d 13m 02.4s||+7.9||02.3"||100||29.302||Aquarius|
|Neptune||25th Jul 2017||23h 01m 07.8s||-07d 17m 12.6s||+7.8||02.3"||100||29.181||Aquarius|