Stargazing October: The mighty Andromeda galaxy reigns

2.5 million light years away, the ‘star’ of autumn is the Andromeda galaxy, with its beautiful spiral shape, young blue stars and pregnant nebulae, write Heather Couper & Nigel Henbest

Centaurus A is a trillion times the mass of our sun (ESO/WFI)

It’s that time of year again, when the trees start to go bare, the weather does a U-turn after 2018’s glorious summer, and the heavens have a fit of the sulks.

Gone are the warm, radiant constellations of our warmer days, to be replaced with the most uninspiring heavens you’ll get to see. The nights are drawing in as the Sun travels down to grace the southern hemisphere (due to the tilt of Earth’s orbit), and the clouds roll in … yes, you’ve guessed it. We’re not keen on autumn.

This time last year, we wrote about the only object of interest at this time of year visible to the unaided eye. As we said last year, find the large, barren Square of Pegasus (high in the south), and trace a line of three stars to its upper left. This is the constellation of Andromeda (supposedly a princess chained to a rock, about to be gobbled up by a sea monster).

Pick out the middle star – and just above, if you have dark, clear skies, you’ll spot the “star” of autumn – the mighty Andromeda galaxy. 2.5 million light years away, it’s huge; through a small telescope, you can see it covers an area four times the size of the full moon. It’s a lot bigger than our Milky Way, too, playing host to a trillion stars (compared to our galaxy’s 200,000 million). Like our galaxy, it’s a beautiful spiral shape, with young blue stars and pregnant nebulae making up its encircling arms.

Now look below that middle star in Andromeda – the same distance as where you saw the Andromeda galaxy above. You’ll need a medium telescope for this one, especially from the light-polluted skies of Britain. This is the Triangulum galaxy: much smaller than Andromeda or the Milky Way. It’s another spiral, and presents itself to us full-frontal. Lying 3 million light years away, it’s claimed that this galaxy is the furthest object you can see with the unaided eye. One slight problem – you have to be in a desert, and blessed with very good eyesight.

Our universe contains billions of galaxies, and there’s a pair of galaxies in Ursa Major above the Plough (see map below) which can be spotted through moderate telescopes. M81 and M82 are both members of a galaxy cluster (galaxies are gregarious), lying a “mere” 12 million light years away. M81 is a serene spiral. But it’s a big galaxy, and it has inflicted gravitational grief on M82, which looks like a cosmic mess. The core of this ragged spiral is suffering a violent outburst of star formation, earning it the title of a “starburst galaxy”.

The night sky at around 11 pm this month (Heather Couper and Nigel Henbest)

Not all galaxies are spiral; they’re the ones that are the most photogenic. Go down to the southern hemisphere and you’ll easily spot two “patches” in the sky. These are the Magellanic Clouds, once classified as “irregular” galaxies. They’re the closest major galaxies to our Milky Way, lying within 200,000 light years. Now astronomers suspect that they may once have been spiral galaxies, but were ripped apart by the Milky Way’s gravity. Irregular galaxies – usually small – are furiously busy at making stars.

On the other hand, elliptical galaxies have done with all that. The most common galaxies in the universe are “dwarf ellipticals” – tiny balls of old, red stars with no cosmic gas to revive starbirth.

But ellipticals can be immense. On your trip down south, take in a view of Centaurus A through binoculars. It’s a whopper of a beast – 1,000 billion times the mass of our sun. It’s currently feeding on a spiral galaxy, whose matter is pouring into a central black hole that weighs in at 55 million suns.

Galaxies – star cities – are the stuff of our cosmos. But don’t be fooled by their glamorous appearance. Most large galaxies (including the Milky Way) harbour supermassive black holes at their cores. Like all big cities – downtown is not where you want to be in a big galaxy. It’s a reminder that we live in a violent universe.

What’s up?

In the southern sky, brilliant Mars is still dominating our early evenings. Though it’s fading as the Earth pulls away, the red planet is still brighter than any of the stars on view.

To its right, you’ll find rather fainter Saturn, now setting about 9.30pm. At the start of the month, you may just catch Jupiter to the right of Saturn. The giant planet is very low in the southwest after sunset, and it’s sinking down into the twilight glow to disappear from view by the middle of October. Distant Uranus is closest to the Earth on 24 October, but – unless you have really dark skies – you’ll need binoculars to spot it in the constellation of Pisces.

So it’s all going to be a bit boring on the planetary front. But the smaller bodies of the solar system are livening things up a bit. Comet Giacobini-Zinner passed the Earth last month, a great sight in binoculars or a telescope but never bright enough to see with the naked eye. In early October, grab a small telescope for a last chance to view the ghostly visitor in the morning sky, to the lower left of Orion.

But we may be treated to some brilliant fragments of this comet lighting up our skies, in the form of shooting stars streaming from the constellation Draco. This Draconid meteor shower takes place every year, but it’s usually only a drizzle of space debris. Because the comet brushed past the Earth only four weeks beforehand, we may be treated to a better show in 2018: look out on the night of 8/9 October – only naked eyes needed!

The night of 21/22 October sees the Orionid meteor shower, fragments from the more famous Halley’s Comet raining down to Earth. Unfortunately, the Moon is almost full that night, and its light will drown out all but the brightest shooting stars.

Diary

6 October, morning: moon near Regulus
8-9 October: Draconid meteor shower
9 October, 4.47am: New moon
11 October: Crescent moon near Jupiter
14 October: Crescent moon near Saturn
16 October, 7.02pm: moon at first quarter
18 October: Moon near Mars
21-22 October: Orionid meteor shower
24 October, 5.45am: Full moon; Uranus at opposition
27 October, morning: Moon near Aldebaran
28 October, 2.00am: British Summer Time ends
31 October, 4.40pm: Moon at last quarter

Just published! For the low-down on all that’s up in the sky next year, check out Heather Couper and Nigel Henbest’s latest book: ‘Philip’s 2019 Stargazing‘