Mercury reaches greatest elongation on July 12th, when it moves out to 26.4 degrees east of the Sun. The planet is visible just after sunset low down above the western horizon in evening twilight. On July 3rd and 4th, Mercury passes within a degree of sprawling open cluster M44, also known as the Praesepe or Beehive cluster. This cluster can be seen with the naked eye under dark skies, but not against the twilight sky. However, it should be visible with binoculars. From northern temperate locations, Mercury rapidly fades from view after greatest elongation and by the third week of the month will be lost to the bright twilight. For those further south, the planets visibility period is better still.
From July 1st to 15th, Mercury fades in brightness from magnitude -0.1 to 0.5. Much brighter Venus, mag. -4.2, appears about 15 degrees above Mercury. On July 14th, the thin waxing crescent Moon passes 2 degrees north of Mercury.
Venus, remains a brilliant early evening object that can be seen throughout July. The planet can be seen above the western horizon as soon as it's dark enough, although it sinks towards the horizon as the month progresses. As previously mentioned, much fainter Mercury can be seen below Venus hugging the horizon.
During July, Venus increases in magnitude -4.1 to -4.3, with its illuminated phase decreasing from 70% to 57%. On July 9th, Venus passes just over a degree north of Regulus (mag. +1.4). Later on July 15th, the waxing crescent Moon passes just north of Venus offering pleasant early evening viewing.
Mars reaches opposition on July 27th when it approaches to within 0.386 AU (approx. 57.7 million kilometres or 35.9 million miles) from the Earth. This month is a very special time for observers of the red planet as it makes its closest approach to Earth since 2003. Currently moving retrograde in Capricornus, Mars rises a couple of hours after the Sun at the beginning of the month, and by months end it's visible all night. As the month progresses its brightness increases from magnitude -2.2 to -2.8. At peak Mars spans some 24.3 arc seconds of apparent size and exceeds 24 arc seconds for a week before and after opposition. Even with a small 80mm (3.1-inch) refractor it's possible to spot prominent details, such as Syrtis Major, on its salmon-pink surface.
On July 1st, the waning gibbous Moon passes 5 degrees north of Mars. On the same day as Mars reaches opposition, a total lunar eclipse is visible from Africa, Asia, South America, Europe and Australia.
Jupiter is visible as soon as it's dark enough. The giant planet is now 2 months past opposition and fades slightly from magnitude -2.3 to -2.1 with its apparent size decreasing from 41.5 to 38 arc seconds as the month progresses. However, it still remains visible until the early hours of the morning.
Jupiter starts the month moving retrograde in Libra. On July 11th it reaches its second stationary point for this year. After that direct motion is resumed with this also being regarded as signalling the end of the current opposition period. Through a small scope, Jupiter's equatorial bands, occasionally the Great Red Spot, and up to four of its Galilean moons can be seen.
On July 20th, the waxing gibbous Moon passes just over 4 degrees north of Jupiter.
Saturn is now just past opposition and remains visible for most all of the night, except for a short time before sunrise. The magnificent ringed planet continues to move retrograde in Sagittarius. Its brightness reduces from magnitude 0.0 to +0.2 during July, with its angular size decreasing slightly from 18.4 to 18.0 arc seconds. The planet is positioned north of the "teapot" asterism of Sagittarius and a few degrees from fifth magnitude globular cluster, M22.
Saturn appears to the naked eye creamy-white. Even a small telescope will show its most famous feature, the spectacular ring system. Also easily visible is Titan, the largest and brightest moon, which at 8th magnitude can be spotted with binoculars. Small scopes reveal other moons including Rhea, Tethys and Dione.
On July 25th, the waxing gibbous Moon passes 2 degrees north of Saturn.
Uranus, mag. +5.8, is located in Aries. The planet rises early morning at the beginning of the month improving to around midnight or just after by months end. Under dark skies Uranus is faintly visible to the naked eye, although from most populated areas optical aid is required.
On July 7th, the waxing gibbous Moon passes 5 degrees south of Uranus.
Neptune continues to move slowly retrograde in Aquarius. With opposition now a couple of months 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 about 30 degrees south and slightly west of the centre of the Great Square of Pegasus. It can be found about a quarter of the way along an imaginary line connecting phi Aquarii (&phi Aqr - mag. +4.2) with lambda Aquarii (&lambda Aqr - mag. +3.7). Although the distance ice giant is the only planet that's not visible to the naked eye, it can easily be seen with binoculars and small telescopes.
Neptune brightens marginally from magnitude +7.9 to +7.8 as the month progresses. On July 4th and 31st, the waning gibbous Moon passes 3 degrees south of the planet.
Solar System Data Table - July 2018
|Date||Right Ascension||Declination||Mag.||App. Size||Illum. (%)||Dist. (AU)||Constellation|
|Sun||Jul 01||06h 38m 40.5s||23d 08m 21.1s||-26.7||31.5'||100||1.017||Gemini|
|Sun||Jul 15||07h 36m 03.8s||21d 36m 09.0s||-26.7||31.5'||100||1.017||Gemini|
|Sun||Jul 31||08h 39m 40.1s||18d 23m 28.3s||-26.7||31.5'||100||1.015||Cancer|
|Mercury||Jul 01||08h 19m 59.4s||20d 57m 06.2s||-0.1||6.6"||61||1.023||Cancer|
|Mercury||Jul 15||09h 22m 12.8s||14d 21m 35.9s||0.5||8.4"||38||0.801||Leo|
|Mercury||Jul 31||09h 32m 38.1s||09d 56m 22.2s||2.6||10.9"||10||0.616||Leo|
|Venus||Jul 01||09h 29m 52.8s||16d 40m 36.3s||-4.1||15.7"||70||1.060||Leo|
|Venus||Jul 15||10h 29m 54.6s||10d 44m 18.3s||-4.2||17.5"||64||0.953||Leo|
|Venus||Jul 31||11h 32m 41.8s||03d 06m 07.3s||-4.3||20.2"||57||0.827||Leo|
|Mars||Jul 01||20h 50m 49.1s||-22d 51m 59.8s||-2.2||20.9"||97||0.449||Capricornus|
|Mars||Jul 15||20h 43m 56.7s||-24d 17m 01.3s||-2.6||23.2"||99||0.404||Capricornus|
|Mars||Jul 31||20h 27m 12.6s||-25d 53m 13.1s||-2.8||24.3"||100||0.385||Capricornus|
|Jupiter||Jul 01||14h 44m 28.8s||-14d 45m 23.0s||-2.3||41.4"||99||4.759||Libra|
|Jupiter||Jul 15||14h 43m 57.3s||-14d 46m 48.8s||-2.2||39.8"||99||4.948||Libra|
|Jupiter||Jul 31||14h 46m 11.0s||-15d 01m 15.2s||-2.1||38.0"||99||5.186||Libra|
|Saturn||Jul 01||18h 23m 07.7s||-22d 28m 56.1s||0.0||18.4"||100||9.050||Sagittarius|
|Saturn||Jul 15||18h 18m 48.4s||-22d 32m 30.4s||0.1||18.3"||100||9.093||Sagittarius|
|Saturn||Jul 31||18h 14m 32.1s||-22d 36m 09.0s||0.2||18.0"||100||9.209||Sagittarius|
|Uranus||Jul 01||01h 59m 03.5s||11d 34m 33.9s||5.8||3.5"||100||20.256||Aries|
|Uranus||Jul 15||02h 00m 22.0s||11d 41m 19.9s||5.8||3.5"||100||20.030||Aries|
|Uranus||Jul 31||02h 01m 08.9s||11d 45m 10.5s||5.8||3.6"||100||19.761||Aries|
|Neptune||Jul 01||23h 10m 42.1s||-06d 20m 15.2s||7.9||2.3"||100||29.535||Aquarius|
|Neptune||Jul 15||23h 10m 11.7s||-06d 24m 01.4s||7.8||2.3"||100||29.330||Aquarius|
|Neptune||Jul 31||23h 09m 12.4s||-06d 30m 49.4s||7.8||2.3"||100||29.138||Aquarius|