Mercury is an early evening object during the second half of October from southern and tropical latitudes. The fast moving planet can be seen low above the western horizon just after sunset. During the visibility period its brightness hardly changes at about magnitude -0.2. By month's end, from mid-latitude southern locations, Mercury sets 1 hour and 45 minutes after the Sun. From mid-latitude northern locations, the planet is not so well placed, but might just be spotted very low in the west towards the tail end of the month.
On October 14th, Mercury (mag. -0.3) passes 7 degrees north of much brighter Venus (mag. -4.5) and on October 30th, Mercury passes 3 degrees south of Jupiter (mag. -1.7).
Venus is an early evening object visible during the first half of the month from southern and equatorial latitudes. However, the planet will move closer to the Sun with each passing day. Observers at mid-latitude northern locations will struggle to spot Venus at all this month.
As previously mentioned on October 14th, Venus and Mercury are located in the same region of sky. Venus reaches inferior conjunction on October 25th.
Mars is located in Capricornus where it spends all of October. As the month progresses, the planet fades from magnitude -1.3 to -0.6 with its disc shrinking from 16 to 12 arc seconds. From northern locations, Mars sets during the evening, although it's visible for considerably longer for those located further south. With a small telescope, of the order of 100mm (4-inch) aperture, it should still be possible to spot details, such as Syrtis Major, on its pink surface.
Jupiter is visible low in the west after sunset. The 'King of the Planets' is now well past its best for this year, but still easily seen. It fades slightly from magnitude -1.8 to -1.7 during October. Jupiter's apparent disk shrinks from 32.6 to 31.4 arc seconds this month. Due to its southerly declination, it's currently better seen from equatorial and southern locations.
On October 11th, the thin waxing crescent Moon passes 4 degrees north of Jupiter and on October 30th, Mercury (mag. -0.2) and Jupiter are separated by only 3 degrees.
Saturn, slowly moving eastwards in Sagittarius, is an evening object visible towards the south-west from northern latitudes and the north from southern locations. The planet is now fading with its brightness reducing from magnitude +0.5 to +0.6 as the month progresses. It also shrinks in apparent size during October from 16.5 to 15.7 arc seconds.
From mid-latitude southern locations, Saturn sets around midnight but considerably earlier for those located in the north. The crescent Moon passes 2 degrees north of Saturn on the 15th.
Uranus is located in south-western Aries close to the Pisces constellation border. The distant planet reaches opposition on October 24th and therefore 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, but easily seen with binoculars and small telescopes.
At opposition, the planet is located approx. 18.875 AU (approx. 2,824 million kilometres or 1,755 million miles) from the Earth. Uranus 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.
On the same day, the full Moon passes 5 degrees south of Uranus.
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. It shines at magnitude +7.8.
The planet can be found about half way along an imaginary line connecting phi Aquarii (φ Aqr - mag. +4.2) with lambda Aquarii (λ Aqr - mag. +3.7). First magnitude star, Fomalhaut (α Psc - mag. +1.2), is about 23 degrees south of Neptune.
On October 20th, the waxing gibbous Moon passes less than three degrees south of the planet.
Solar System Data Table - October 2018
|Date||Right Ascension||Declination||Mag.||App. Size||Illum. (%)||Dist. (AU)||Constellation|
|Sun||Oct 01||12h 27m 36.0s||-02d 58m 51.8s||-26.7||31.9'||100||1.001||Virgo|
|Sun||Oct 15||13h 18m 51.3s||-08d 19m 08.5s||-26.8||32.1'||100||0.997||Virgo|
|Sun||Oct 31||14h 19m 37.5s||-13d 55m 53.8s||-26.8||32.2'||100||0.993||Virgo|
|Mercury||Oct 01||12h 56m 47.5s||-05d 27m 02.9s||-0.9||4.8"||98||1.406||Virgo|
|Mercury||Oct 15||14h 18m 30.8s||-14d 56m 43.2s||-0.3||5.0"||90||1.335||Virgo|
|Mercury||Oct 31||15h 46m 51.5s||-22d 31m 38.8s||-0.2||5.9"||75||1.138||Libra|
|Venus||Oct 01||14h 21m 46.9s||-21d 19m 23.3s||-4.8||46.2"||17||0.361||Virgo|
|Venus||Oct 15||14h 15m 55.5s||-21d 29m 21.2s||-4.4||56.7"||5||0.294||Virgo|
|Venus||Oct 31||13h 44m 36.6s||-16d 33m 47.0s||-4.3||60.9"||1||0.274||Virgo|
|Mars||Oct 01||20h 36m 20.3s||-22d 36m 42.5s||-1.3||15.8"||88||0.592||Capricornus|
|Mars||Oct 15||21h 01m 03.8s||-20d 13m 07.5s||-1.0||13.9"||87||0.676||Capricornus|
|Mars||Oct 31||21h 34m 04.7s||-16d 55m 42.5s||-0.6||12.0"||86||0.781||Capricornus|
|Jupiter||Oct 01||15h 18m 26.1s||-17d 28m 59.4s||-1.8||32.6"||100||6.046||Libra|
|Jupiter||Oct 15||15h 29m 29.9s||-18d 11m 53.5s||-1.8||31.9"||100||6.178||Libra|
|Jupiter||Oct 31||15h 43m 11.7s||-19d 00m 33.8s||-1.7||31.4"||100||6.285||Libra|
|Saturn||Oct 01||18h 12m 01.8s||-22d 45m 47.1s||0.5||16.5"||100||10.097||Sagittarius|
|Saturn||Oct 15||18h 15m 03.9s||-22d 46m 41.0s||0.5||16.1"||100||10.324||Sagittarius|
|Saturn||Oct 31||18h 19m 57.7s||-22d 46m 37.2s||0.6||15.7"||100||10.563||Sagittarius|
|Uranus||Oct 01||01h 57m 02.2s||11d 21m 54.8s||5.7||3.7"||100||18.952||Aries|
|Uranus||Oct 15||01h 54m 58.1s||11d 10m 36.0s||5.7||3.7"||100||18.886||Aries|
|Uranus||Oct 31||01h 52m 28.4s||10d 57m 00.1s||5.7||3.7"||100||18.884||Aries|
|Neptune||Oct 01||23h 03m 19.7s||-07d 08m 27.8s||7.8||2.4"||100||29.018||Aquarius|
|Neptune||Oct 15||23h 02m 08.6s||-07d 15m 42.1s||7.8||2.3"||100||29.142||Aquarius|
|Neptune||Oct 31||23h 01m 07.2s||-07d 21m 46.9s||7.8||2.3"||100||29.341||Aquarius|