ow far can you see with your unaided eye? It’s a question that gets everyone intrigued. We’re all used to spotting landmarks several kilometres away, and from the top of the Shard in London, it’s reckoned you can see over 50kms.
But that’s just looking around us. Gaze upwards and you’re in a different realm. The moon is 384,000kms away, the sun 150 million kms from us, and the stars millions of millions of kilometres away – so far off that their light takes years to reach us. Even that pales into insignificance compared to an object high in the sky this month. The light from the Andromeda galaxy has travelled for literally millions of years before it hits your eyeball.
Go out on a clear night, away from streetlights and when the moon isn’t in the sky – the middle of this month is ideal – and look almost overhead in the south. Below the pale band of the Milky Way arching over the sky, you’ll spot the Andromeda galaxy as a faint smudge of light (see the starchart for help identifying it).
To be fair, there are a couple of more distant galaxies that people with exceptional eyesight and totally dark desert skies may able to pick out, but Andromeda is the most remote object that most of us will ever see without resorting to binoculars or a telescope, 2.5 million light years away.
To be visible at this immense distance, Andromeda must be incredibly bright: it shines with the light of a trillion stars. They are mainly arranged in a flat disc, tipped up to our view, thick in dust and gas where new stars are being born. The disc sports spiral arms that look impressive in photographs, but a word of warning: even with a telescope, your eye won’t see Andromeda as anything more than a milky blur.
The galaxy’s central bulge is made of old stars, dating back to just after the time of the Big Bang. And right at the centre is a giant black hole. While the black hole at the core of the Milky Way weighs as much as four million suns, the central monster in Andromeda outweighs our local star 100 million times over.
Beyond the visible stars, a vast cloud of gas envelopes Andromeda. Measurements announced just a couple of months ago show that this halo extends over a million light years in every direction, halfway towards the Milky Way.
Finally, while all the other major galaxies in the universe are speeding away from us, Andromeda is coming towards the Milky Way, at 400,000kms per hour. From its distance and its speed, astronomer calculate it will crash into our galaxy in four billion years’ time. After a huge burst of cosmic fireworks, the stars of the two galaxies will combine into a single mammoth galaxy, that astronomers have dubbed Milkomeda.
Giant planet Jupiter is lording it over the south-western sky after sunset, brighter than anything in the evening sky (bar the moon), with its sidekick Saturn just to the left. After its brilliant show last month, Mars is now fading as the Earth pulls away, but it’s still more brilliant than any star. You’ll find the red planet in the southern sky during the evening.
And Mars acts as a convenient signpost to find your way around some of the fainter constellations on view this month. A triangle of stars below marks the hindquarters of Cetus (the Sea Monster): his head is depicted by a quadrangle of stars between Mars and the Pleiades – the twinkling Seven Sisters star cluster.
The stars above and to the right of Mars form Pisces, a pair of fishes joined at their tails. To the upper left of the red planet, three stars in a bent line depict the celestial Ram, Aries.
Most distinctively, a large square of stars to the upper right of Mars marks out the body of Pegasus, the Flying Horse. His head and neck stretch downwards from the righthand star: if you look at the starchart, you’ll see that the star marking the horse’s nose – Enif – points upwards. That’s because old sky maps, for reasons best known to the ancients, showed Pegasus flying upside-down.
And from the left-hand star of the Square of Pegasus, a line of stars depicts princess Andromeda, and above them lies the great Andromeda galaxy.
If you’re out-and-about on the night of 17 November, you may catch some shooting stars of the Leonid meteor shower. In the past, we have occasionally been treated to a real storm of Leonids, but we’re not expecting a major display this year as the comet shedding the meteor particles is a long way from Earth.
Finally, in the morning sky, Venus is totally resplendent, rising around 4am in east. In the middle of November, you have a good chance to spot elusive Mercury, putting on its best morning appearance of the year. The innermost planet lies to the lower left of Venus, rising about 5.30am.
6 November: Moon near Castor and Pollux
8 November, 1.46pm: Last Quarter Moon
10 November: Mercury at greatest western elongation
12 November (am): Moon near Venus
13 November (am): Moon between Venus and Mercury
15 November, 5.07am: New moon
17 November: Maximum of Leonid meteor shower
19 November: Moon near Jupiter and Saturn
22 November, 4.45am: First quarter moon
25 November: Moon near Mars
29 November: Moon between Aldebaran and the Pleiades
30 November, 9.29am: Full moon near Aldebaran