Mercury

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.

Mercury 45 minutes after sunset from mid-latitude southern locations on July 30, 2017 (credit:- stellarium/freestarcharts)

Venus

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

Mars reaches solar conjunction on July 27th and is therefore unsuitably placed for observation throughout the month.

Jupiter

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.

Jupiter during July 2017 (credit:- freestarcharts)

Jupiter during July 2017 - pdf format (credit:- freestarcharts)

Saturn

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.

Saturn as imaged by the Cassini space probe (credit:- NASA/JPL-Caltech/SSI)

Saturn during July 2017 (credit:- freestarcharts)

Saturn during July 2017 - pdf format (credit:- freestarcharts)

Uranus

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.

Uranus during July 2017 (credit:- freestarcharts)

Uranus during July 2017 - pdf format (credit:- freestarcharts)

Neptune

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.

Neptune during July 2017 (credit:- freestarcharts)

Neptune during July 2017 - pdf format (credit:- freestarcharts)

Solar System Data Table July 2017

 DateRight AscensionDeclinationApparent MagnitudeApparent SizeIllum. (%)Distance from Earth (AU)Constellation
Sun5th Jul 201706h 56m 15.0s22d 48m 27.3s-26.731.5'1001.017Gemini
Sun15th Jul 201707h 37m 05.0s21d 33m 47.9s-26.731.5'1001.016Gemini
Sun25th Jul 201708h 17m 07.1s19d 42m 28.4s-26.731.5'1001.016Cancer
Mercury5th Jul 201708h 01m 28.1s22d 24m 54.1s-0.805.4"851.235Cancer
Mercury15th Jul 201709h 11m 09.4s17d 27m 05.5s-0.206.1"691.098Cancer
Mercury25th Jul 201710h 02m 37.7s11d 39m 40.2s0.107.1"540.948Leo
Venus5th Jul 201703h 52m 34.6s17d 33m 19.0s-4.217.6"640.950Taurus
Venus15th Jul 201704h 38m 26.2s19d 46m 30.4s-4.116.3"681.025Taurus
Venus25th Jul 201705h 26m 21.6s21d 17m 52.1s-4.015.2"721.098Taurus
Mars5th Jul 201707h 25m 57.1s23d 00m 36.3s+1.703.6"1002.628Gemini
Mars15th Jul 201707h 53m 40.6s21d 57m 20.0s+1.703.5"1002.644Gemini
Mars25th Jul 201708h 20m 48.8s20d 37m 51.2s+1.703.5"1002.654Cancer
Jupiter5th Jul 201712h 53m 14.2s-04d 18m 00.1s-2.036.9"995.339Virgo
Jupiter15th Jul 201712h 56m 19.9s-04d 40m 03.1s-2.035.9"995.494Virgo
Jupiter25th Jul 201713h 00m 19.3s-05d 07m 24.0s-1.934.9"995.645Virgo
Saturn5th Jul 201717h 29m 12.5s-21d 55m 34.2s+0.118.3"1009.098Ophiuchus
Saturn15th Jul 201717h 26m 30.1s-21d 54m 50.0s+0.218.1"1009.169Ophiuchus
Saturn25th Jul 201717h 24m 13.3s-21d 54m 28.9s+0.217.9"1009.264Ophiuchus
Uranus5th Jul 201701h 44m 37.5s10d 12m 16.9s+5.803.5"10020.161Pisces
Uranus15th Jul 201701h 45m 21.9s10d 16m 12.7s+5.803.5"10019.995Pisces
Uranus25th Jul 201701h 45m 48.4s10d 18m 26.6s+5.803.6"10019.827Pisces
Neptune5th Jul 201723h 02m 11.5s-07d 09m 52.6s+7.902.3"10029.442Aquarius
Neptune15th Jul 201723h 01m 44.7s-07d 13m 02.4s+7.902.3"10029.302Aquarius
Neptune25th Jul 201723h 01m 07.8s-07d 17m 12.6s+7.802.3"10029.181Aquarius

Sky Highlights - July 2017

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for July

Meteor Shower
Southern Delta Aquariids (Aquarids) meteor shower peaks on July 29

Northern Hemisphere
Evening
West:- Mercury (mag. -0.5 to +0.3) (second half of month)
Southwest:- Jupiter (mag. -2.0)
South:- Saturn (mag. +0.2)
Midnight
West:- Jupiter
South:- Saturn
East:- Neptune (mag. +7.8)
Morning
Southwest:- Saturn
South:- Neptune
Southeast:- Uranus (mag. +5.8)
East:- Venus (mag. -4.1)

Southern Hemisphere
Evening
West:- Mercury (second half of month)
Northwest:- Jupiter
East:- Saturn
Midnight
West:- Jupiter
North:- Saturn
East:- Neptune
Morning
West:- Saturn
North:- Neptune
Northeast:- Venus, Uranus

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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