Our celestial neighbourhood in October
PICK OF THE MONTH
Neptune
Best time to see: 1 October, 23:00 UT
Altitude: 33º Location: Aquarius
Direction: South
Features: Colour, occasional atmospheric effects, Triton
Recommended equipment: 200mm or larger
Neptune was at opposition in the middle of September and remains very well placed for observation from the UK throughout October. By the end of the month, shining at mag. +7.8, Neptune and mag. –2.6 Jupiter will appear separated by just 6.7˚, both planets being located below the faint Circlet asterism in Pisces. The separation continues to reduce into next month, reaching a minimum of around 6.1˚ in late November.
At mag. +7.8, Neptune is too faint to be seen with the naked eye, theoretically being the only one of the main planets that needs optical assistance to see. In reality, it’s difficult to spot Uranus too, which often lurks on the threshold of naked-eye visibility, and binoculars are your best choice to try to secure a view of both worlds.
Through a 75mm telescope at high power, it’s possible to get a feel that Neptune’s blue-hued dot isn’t a star, but a larger scope, say over 150mm diameter, is recommended to confirm this view. If you suspect you’ve got it in your field of view but aren’t sure, centre it and gradually increase the power. If the atmospheric stability Þ Neptune and its largest moon Tri ton: viable targets (seeing) is poor, don’t go too for 200mm high with the magnification. A power of 150x or more should reveal Neptune as a planet.
The larger the aperture you use the easier it will be to see Neptune’s tiny 2.4-arcsecond disc. Large planetary imaging setups may, on occasion, pick up vague detail within the planet’s atmosphere, including banding and large-scale storms. Being the most distant of the main planets, Neptune doesn’t give up its secrets easily, but amazingly its scopes largest moon, Triton, can be seen quite easily through a 200mm instrument. Triton shines at mag. +13.5.
Mercury
Best time to see: 8 October, 30 minutes before sunrise
Altitude: 12˚
Location: Virgo
Direction: East
A morning planet on 1 October, mag. +1.4 Mercury rises 70 minutes before the Sun. It improves markedly and by 8 October at mag. –0.2, reaches greatest western elongation, rising 100 minutes before sunrise. It remains well-placed to around 20 October, at mag. –0.9. It remains bright, but its rising offset from the Sun then reduces. On 24 October, mag. –1.0 Mercury, preceded by a 1%-lit Moon, rises an hour before the Sun. By the end of the month, the rise time offset decreases to just 30 minutes.
Venus
Best time to see: 1 October, 20 minutes before sunrise
Altitude: 2˚ (extremely low)
Location: Virgo
Direction: East
Rising just 40 minutes before the Sun on 1 October, mag. –3.8 Venus is now becoming hard to see. Venus reaches superior conjunction on 22 October, thereafter reemerging into the evening sky.
Mars
Best time to see: 31 October, 03:00 UT
Altitude: 61˚
Location: Taurus
Direction: South
Mars is now a major planet in the late evening to early morning sky. Rising in the northeast around 20:30 UT on 1 October, it reaches 60˚ as dawn breaks. Shining at mag. –0.6 on this date, it presents an apparent disc size of 11 arcseconds. Passing just over 1˚ north of the Crab Nebula, M1, mid-month, Mars is joined by a 73%-lit Moon 3˚ to the north on 15 October. As the month ends, Mars shines at mag. –1.2 and is 15 arcseconds across.
Jupiter
Best time to see: 1 October, 23:40 UT
Altitude: 37˚
Location: Pisces
Direction: South
Following opposition, Jupiter remains superbly positioned. On 1 October, it shines at mag. –2.8, east and slightly south of the Circlet asterism in Pisces. On 8 October, it is joined by an almost full Moon less than 3˚ to the south as they rise. By 31 October, it appears at mag. –2.7 and reaches its highest position in the sky, due south at 21:30 UT, at an altitude of 35˚ from the centre of the UK.
Saturn
Best time to see: 1 October, 21:00 UT
Altitude: 21˚
Location: Capricornus
Direction: South
At mag. +0.6 on 1 October, dimming to mag. +0.8 by the end of the month, Saturn reaches its highest position due south, under dark sky conditions all month, reaching 20˚ altitude as seen from the centre of the UK. A bright 81%-lit Moon lies nearby on the evening of 5 October.
Uranus
Best time to see: 31 October, 00:30 UT
Altitude: 53˚
Location: Aries
Direction: South
Uranus is extremely wellplaced for UK viewing, appearing over 50˚ up when due south, from the centre of the UK. A 94%-lit waning gibbous Moon lies 2.5˚ west at 01:50 UT on 12 October.
The planets in October
The phase and relative sizes of the planets this month. Each planet is shown with south at the top, to show its orientation through a telescope
JUPITER’S MOONS: OCTOBER
Using a small scope you can spot Jupiter’s biggest moons. Their positions change dramatically over the month, as shown on the diagram. The line by each date represents 01:00 BST (00:00 UT.)
