Mercury reaches superior conjunction on the far side of the Sun on October 8th. From northern locations, the planet is not visible this month but may be seen just after sunset towards the end of month from southern latitudes, close to the west-northwestern horizon.
Venus, mag. -3.9, continues to move back towards the Sun but remains a morning object for most of October. From northern temperate locations, the brilliant planet can be seen low down above the eastern horizon just before sunrise, although by month's end observers may have difficulty spotting it against the bright twilight. Venus can also be seen from southern locations, but with a reduced visibility period.
On October 3rd, Venus reaches perihelion when it's 0.718 AU (approx. 107 million kilometres or 66.7 million miles) from the Sun. A close conjunction occurs on October 5th when Venus and Mars are separated by only 1/5 of a degree. At mag. +1.8, Mars appears almost 200x fainter than Venus and binoculars will help to spot it. On the mornings of October 17th and 18th, the thin waning crescent Moon appears near the two planets creating pleasant viewing.
Mars, mag. +1.8, is now an early morning object visible towards the east before sunrise. The red planet starts the month in Leo before crossing into Virgo on the 12th, where it stays for the remainder of the month. Mars is not visually striking, but does rise slightly earlier in the sky each morning as the month progresses. As previously mentioned, much brighter Venus passes close by the planet on the 5th and the thin waning crescent Moon joins the pair in the morning skies of the 17th and 18th.
Mars reaches aphelion on October 7th, when it's 1.666 AU (approx. 249.2 million kilometres or 154.9 million miles) from the Sun.
Jupiter, mag. -1.7, passes through solar conjunction on October 27th. This month the planet is only likely to be seen during the first two weeks from southern and tropical latitudes, low down above the western horizon just after sunset.
Saturn, mag. +0.6, remains an early evening object in Ophiuchus. It's visible just after sunset towards the southwest from northern latitudes and towards the west from southern locations. The visibility period continues to diminish each day and by month's end from mid-northern temperate latitudes it will be setting just a couple of hours after the Sun, although up to 3.5 hours for those living further south.
On October 16th, Saturn's rings reach their maximum tilt at 27 degrees and on October 24th, the waxing crescent Moon passes 3 degrees north of the planet.
Uranus is located in Pisces close to the Aries constellation border. The distant planet reaches opposition on October 19th and therefore is visible all night long. It rises above the eastern horizon at sunset, reaches its highest point in the sky around midnight before setting in the west as the Sun re-appears. At mag. +5.7, Uranus is faintly visible to the naked eye under dark skies and easily visible with binoculars and small telescopes.
At opposition, Uranus is located approx. 18.915 AU (approx. 2,830 million kilometres or 1,758 million miles) from Earth. The planet has an apparent diameter of 3.7 arc seconds and through a telescope at high magnifications it appears as a small but obviously non-stellar green disk. However, even with the large amateur scopes, it's difficult to make out any atmospheric details.
The almost full Moon passes 4 degrees south of Uranus on October 6th.
Neptune continues to move very slowly retrograde in Aquarius. The most distant planet is now a month passed opposition but remains well placed for observation throughout the month. It can be seen just after sunset and remains visible for most of the night. Although beyond naked eye visibility, Neptune is relatively easy to spot with binoculars or small scopes. During October, it fades slightly in brightness from mag. +7.8 to +7.9.
The planet is positioned about 30 degrees south of the centre of the Great Square of Pegasus and a fraction of a degree southeast of lambda Aqr (λ Aqr - mag. +3.7). First magnitude star, Fomalhaut (α Psc - mag. +1.2), is 22 degrees directly to the south.
On October 3rd and again on the 30th, the waxing gibbous Moon passes less than a degree south of the planet.
Solar System Data Table October 2017
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||Oct 5||12h 43m 03.3s||-04d 37m 42.6s||-26.7||32.0'||100||1.000||Virgo|
|Sun||Oct 15||13h 19m 48.3s||-08d 24m 50.0s||-26.8||32.1'||100||0.997||Virgo|
|Sun||Oct 25||13h 57m 29.4s||-12d 00m 12.8s||-26.8||32.2'||100||0.994||Virgo|
|Mercury||Oct 5||12h 34m 19.9s||-02d 07m 28.3s||-1.6||04.9"||99||1.383||Virgo|
|Mercury||Oct 15||13h 36m 49.2s||-09d 34m 39.9s||-1.2||04.7"||99||1.426||Virgo|
|Mercury||Oct 25||14h 37m 19.2s||-16d 03m 34.9s||-0.6||04.8"||96||1.405||Libra|
|Venus||Oct 5||11h 18m 22.5s||05d 57m 25.1s||-3.9||11.0"||91||1.512||Leo|
|Venus||Oct 15||12h 04m 08.6s||01d 11m 47.6s||-3.9||10.8"||93||1.552||Virgo|
|Venus||Oct 25||12h 49m 55.0s||-03d 40m 55.5s||-3.9||10.5"||95||1.587||Virgo|
|Mars||Oct 5||11h 19m 38.3s||05d 36m 56.4s||1.8||03.7"||99||2.538||Leo|
|Mars||Oct 15||11h 42m 56.0s||03d 06m 49.6s||1.8||03.8"||98||2.495||Virgo|
|Mars||Oct 25||12h 06m 07.0s||00d 35m 24.7s||1.8||03.8"||98||2.445||Virgo|
|Jupiter||Oct 5||13h 47m 41.6s||-09d 59m 55.9s||-1.7||30.8"||100||6.393||Virgo|
|Jupiter||Oct 15||13h 55m 51.1s||-10d 45m 48.0s||-1.7||30.7"||100||6.425||Virgo|
|Jupiter||Oct 25||14h 04m 10.0s||-11d 31m 10.8s||-1.7||30.6"||100||6.435||Virgo|
|Saturn||Oct 5||17h 26m 28.0s||-22d 09m 15.5s||0.6||16.1"||100||10.352||Ophiuchus|
|Saturn||Oct 15||17h 29m 25.8s||-22d 13m 08.1s||0.6||15.8"||100||10.503||Ophiuchus|
|Saturn||Oct 25||17h 32m 55.3s||-22d 17m 01.8s||0.6||15.6"||100||10.642||Ophiuchus|
|Uranus||Oct 5||01h 40m 35.5s||09d 47m 39.0s||5.7||03.7"||100||18.945||Pisces|
|Uranus||Oct 15||01h 39m 04.6s||09d 39m 00.6s||5.7||03.7"||100||18.917||Pisces|
|Uranus||Oct 25||01h 37m 31.9s||09d 30m 12.9s||5.7||03.7"||100||18.920||Pisces|
|Neptune||Oct 5||22h 54m 24.2s||-07d 59m 40.7s||7.8||02.3"||100||29.075||Aquarius|
|Neptune||Oct 15||22h 53m 36.5s||-08d 04m 27.0s||7.8||02.3"||100||29.175||Aquarius|
|Neptune||Oct 25||22h 52m 57.4s||-08d 08m 17.3s||7.9||02.3"||100||29.298||Aquarius|