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Mercury

Mercury passed through inferior conjunction at the end of September and at the start of October remains too close to the Sun to be visible. However, the planet moves fast and just over two weeks later on October 16th it reaches greatest western elongation (18.1 degrees). As a result, Mercury is visible as an early morning object from northern temperate locations - and to a lesser extent from tropical latitudes - from about the first week of October until the last few days of the month.

This also happens to be the most favourable morning apparition of the year for observers at these latitudes. For example, from 52N (e.g. London, England) the planet will be 9 degrees above the east-southeastern horizon 45 minutes before sunrise on October 16th. Mercury's altitude then decreases gradually each subsequent day until it's lost to the morning twilight at months end. During the visibility period the planet brightens rapidly from mag. +1.3 to -1.0. In the same area of sky about 25 degrees to the northwest are Venus (mag. -4.5), Jupiter (mag. -1.8) and Mars (mag. +1.8).

On October 11th, the waning crescent Moon passes 0.9 degrees south of Mercury with an occultation visible from South S. America and the Falkland Islands. The following day the planet reaches perihelion at 0.307 AU (approx. 45.9 million kilometres or 28.5 million miles) from the Sun.

For Southern Hemisphere observers, Mercury is inconveniently placed for observation this month.

October evening apparition of Mercury from a latitude of 52N (credit:- freestarcharts)

Venus

Venus like Mercury also reaches greatest western elongation this month; on October 26th it moves out to 46 degrees from the Sun. The unmistakable planet is a blazing beacon of light in the eastern morning sky, visible for over 4 hours by months end from northern temperate latitudes although only about half this time from the Southern Hemisphere.

Venus is so bright that it easily outshines any other planet in the Solar System or any night-time star. This month the dazzling planet is not alone in the early morning sky, Jupiter and Mars are nearby. Those at northern latitudes will also be able to spot a fourth planet, Mercury, low down above the horizon from the first week of the month.

On October 8th, the waning crescent Moon passes 0.7 degrees south of Venus with an occultation visible from Australia and New Zealand at 20:33 UT. The next day, Venus passes 2.5 degrees south of Regulus (α Leo - mag. +1.4) with the waning crescent Moon, Mars and Jupiter all close by. For comparison, Venus is 12 times brighter than Jupiter with Jupiter 25 times brighter than Mars!

Later on October 26th, Venus passes 1.1 degrees south of Jupiter. This month there are many wonderful viewing and photo opportunities with these planets grouped so closely together.

Venus, Jupiter and Mars during October 2015 (credit:- freestarcharts)

Venus, Jupiter and Mars during October 2015 - pdf format (credit:- freestarcharts)

Mars

Mars is an early morning object in Leo during October. From northern temperate latitudes it's visible towards the east for 3 hours before sunrise at the start of the month, improving to over 4 hours by months end. However, the planet is less well placed for those living further south.

The magnitude of Mars improves slightly from +1.8 to +1.7 although it's not particularly bright. However, the planet's close proximity to Venus and Jupiter will aid significantly in locating it. With the Earth now slowly closing in on "The Red Planet" its visibility will gradually improve month by month until opposition is reached on May 22, 2016. Mars will then shine at magnitude -2.1, almost 40 times brighter than it appears now! Telescopically observers have the chance then to study or image the Martian surface in some detail, something that's currently impossible due to its small apparent size of just 4 arc seconds.

On October 9th, the waning crescent Moon passes 3 degrees south of Mars. As previously mentioned this forms a wonderful pre-dawn setting along with Venus, Jupiter and Regulus. Later on the 17th, Mars passes 0.4 degrees north of Jupiter with both planets easily fitting into the same low/medium magnification telescope eyepiece field of view.

Jupiter, Mars, Venus, Regulus and the Moon - 90 minutes before sunrise on October 9th as seen from mid Northern Latitudes (credit:- Stellarium)

Jupiter, Mars, Venus, Regulus and the Moon - one hour before sunrise on October 9th as seen from mid Southern Latitudes (credit:- Stellarium)

Jupiter

Jupiter is now a beautiful early morning object moving direct among the stars of Leo. During October its brightness and apparent size improve slightly from magnitude -1.7 to -1.8 and 31 to 33 arc seconds respectively. What makes for wonderful pre-dawn spectacles this month is Jupiter's close proximity to even more brilliant Venus. At start of month, Venus is about 15 degrees west of Jupiter. On October 26 it overtakes the giant planet passing 1.1 degrees to the north before ending the month about 5 degrees further to the southeast.

The waxing Moon passes 3 degrees south of Jupiter on October 10th and as previously mentioned Jupiter passes less than half a degree south of Mars on October 17th.

Saturn

Saturn, mag. +0.6, is an early evening object that's visible as soon as it's dark enough. On October 1st from northern temperate latitudes it appears a few degrees above the southwestern horizon, setting about 2 hours after the Sun. The visibility period of the planet continues to diminish as the month progresses and by the end of October it will be inconveniently submerged in the twilight at dusk. Saturn is somewhat easier to see further south. From southern temperate latitudes the "Ringed planet" is visible for up to twice as long.

The thin waxing crescent Moon passes 3 degrees north of the planet on October 16th. On the same day, Saturn eastward motion carries it across the constellation boundary into Scorpius from Libra. Located 10 degrees to the southeast is first magnitude star Antares (α Sco mag. +1.0).

Saturn during October 2015 (credit:- freestarcharts)

Saturn during October 2015 - pdf format (credit:- freestarcharts)

Uranus

Uranus reaches opposition on October 12th in Pisces and is therefore visible all night. The distant Ice World rises above the eastern horizon at sunset, reaches its highest point in the sky during the middle of the night before setting in the west as the Sun re-appears. At magnitude +5.7, the planet is faintly visible to the naked eye under dark skies. Even if you can't spot Uranus with the naked eye it's a very easy binocular target.

Uranus as imaged by the Hubble Space Telescope (credit:- NASA/Lamy)

At opposition, Uranus is located approx. 18.984 AU (approx. 2840 million km or 1765 million miles) from Earth. The planet has an apparent diameter of 3.7 arc seconds and a small telescope at high magnification will show it as a small green disk, obviously non-stellar. However, even when viewed through the largest of amateur scopes it's difficult to make out any details.

On October 26th, the full Moon passes 0.9 degrees south of Uranus with an occultation visible from New Zealand at 10:25 UT.

Uranus during October 2015 (credit:- freestarcharts)

Uranus during October 2015 - pdf format (credit:- freestarcharts)

Neptune

Neptune continues to move very slowly retrograde in Aquarius during October. The most distant planet in the Solar System is now one month passed opposition but remains well placed for observation, visible as soon as it's dark enough and for most of the night. Neptune is too faint to be seen with the naked eye but relatively easy to spot with binoculars. During October it fades slightly from magnitude +7.8 to +7.9.

Aquarius is the tenth largest constellation in the sky but it's faint. Its brightest star Sadalsuud (β Aqr) shines at only magnitude +2.9 and most other stars are considerably fainter. Despite this once familiar with the surrounding area of sky locating Neptune isn't that difficult. The planet is currently positioned towards the constellation centre about three quarters along an imaginary line connecting lambda Aqr (λ - mag. +3.7) with sigma Aqr (σ Aqr - mag. +4.8).

On October 23rd, the waxing gibbous Moon passes 3 degrees north of Neptune.

Neptune during October 2015 (credit:- freestarcharts)

Neptune during October 2015 - pdf format (credit:- freestarcharts)

Solar System Data Table October 2015

 DateRight AscensionDeclinationApparent MagnitudeApparent SizeIllum. (%)Distance from Earth (AU)Constellation
Sun5th Oct 201512h 41m 16.2s-04d 26m 22.3s-26.732.0'1001.000Virgo
Sun15th Oct 201513h 17m 59.8s-08d 14m 00.0s-26.832.1'1000.997Virgo
Sun25th Oct 201513h 55m 37.2s-11d 50m 03.4s-26.832.2'1000.995Virgo
Mercury5th Oct 201512h 07m 43.6s-01d 56m 36.7s3.109.6"060.701Virgo
Mercury15th Oct 201512h 13m 58.5s00d 12m 17.9s-0.507.2"490.940Virgo
Mercury25th Oct 201513h 02m 50.3s-04d 31m 46.6s-0.905.6"841.195Virgo
Venus5th Oct 201509h 52m 35.4s10d 07m 53.5s-4.631.2"380.534Leo
Venus15th Oct 201510h 26m 07.1s08d 26m 21.3s-4.527.4"440.608Leo
Venus25th Oct 201511h 03m 04.0s05d 56m 15.0s-4.424.4"500.683Leo
Mars5th Oct 201510h 32m 55.0s10d 31m 20.6s1.804.0"972.368Leo
Mars15th Oct 201510h 56m 14.6s08d 13m 33.8s1.804.1"962.312Leo
Mars25th Oct 201511h 19m 07.8s05d 52m 38.9s1.704.2"962.250Leo
Jupiter5th Oct 201510h 52m 56.4s08d 08m 05.3s-1.731.6"1006.242Leo
Jupiter15th Oct 201511h 00m 20.2s07d 24m 00.7s-1.832.0"1006.154Leo
Jupiter25th Oct 201511h 07m 18.7s06d 42m 14.4s-1.832.6"1006.048Leo
Saturn5th Oct 201515h 57m 32.3s-18d 40m 51.7s0.615.7"10010.613Libra
Saturn15th Oct 201516h 01m 25.3s-18d 53m 46.1s0.615.5"10010.731Libra
Saturn25th Oct 201516h 05m 40.1s-19d 07m 05.8s0.615.3"10010.830Scorpius
Uranus5th Oct 201501h 09m 33.0s06d 39m 21.9s5.703.7"10018.991Pisces
Uranus15th Oct 201501h 08m 02.3s06d 30m 09.6s5.703.7"10018.986Pisces
Uranus25th Oct 201501h 06m 32.7s06d 21m 06.9s5.703.7"10019.012Pisces
Neptune5th Oct 201522h 37m 18.5s-09d 34m 50.7s7.802.3"10029.127Aquarius
Neptune15th Oct 201522h 36m 33.7s-09d 39m 10.6s7.802.3"10029.236Aquarius
Neptune25th Oct 201522h 35m 58.4s-09d 42m 32.2s7.902.3"10029.367Aquarius