The night sky for October 2016

Northern Hemisphere

Ian Morison tells us what we can see in the Northern hemisphere night sky during October 2016.

Highlights of the Month

October – A good month to observe Uranus with a small telescope.

Uranus comes into opposition – when it is nearest the Earth – on the night of the 15th of October, so will be seen well this month – particularly from around the beginning and end of the month when no moonlight will intrude. Its magnitude is +5.9 so Uranus should be easily spotted in binoculars lying in the southern part of Pisces to the east of the Circlet asterism and east-southeast of 4th magnitude stars Epsilon Piscium and Delta Piscium as shown on the chart. It rises to an elevation of ~45 degrees when due south. Given a telescope of 4 inches it should be possible to see that it has a disk (3.6 arc seconds across) which has a pale green-blue tint. With an 8 inch telescope and good seeing, perhaps using a green filter it may even be possible to see some detail in the planet’s cloud features which appear to be more prominent than usual. That is an observing challenge! Four of its satellites, Arial(+14.4), Umbrial(+15), Titania (+13.9) and Oberon (+14.1) can also be seen given a night of good seeing and a telescope of 8 inches diameter or more.

October 3rd – after sunset: Venus and a very thin crescent Moon

As twilight fades on the 3rd of October and given clear skies and a very low horizon in the south-west you may be able to spot Venus lying down to the left of a very thin crescent Moon, just 6.7percent illuminated. This gives you a chance of observing ‘earthshine’, the ‘dark’ side of the Moon faintly illuminated by light reflected from the Earth.

October 8th, – one hour after sunset: the first quarter Moon lies above Mars

After sunset, looking south and given clear skies, the first quarter Moon will be visible lying up to the left of Mars shining at magnitude +0.15. Mars, in Sagittarius, is lying just to the left of the top star of the Teapot, Lambda Sagittarii.

Observe the International Space StationUse the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset – this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK and across the world.

Find details of sighting possibilities from your location from the location index. See where the space station is now using the tracking page.

The Planets

  • JupiterJupiter having passed behind the Sun last month, will appear again low above the eastern horizon around the 8th of October. On the 11th, Jupiter at magnitude -1.7 lies close to Mercury but they will only be ~5 degrees above the horizon 30 minutes before sunrise. As the month progreses, Jupiter rises a little earlier so that by month’s end and still at magnitude -1.7, it rises some two and a half hours before the Sun. A low eastern horizon and the use of binoculars may well be needed but please do not use them after the Sun has risen. As the Earth moves towards Jupiter, the size of Jupiter’s disk increases slightly from 30.6 to 31.2 arc seconds so early risers at the end of the month should be able to observe the equatorial bands in the atmosphere and the four Gallilean moons as they weave their way around it.
  • SaturnOn September 11th, Saturn, lying in Ophiuchus, was just 6 degrees above, and a little to the left, of Antares in Scorpius. It is moving slowly eastwards but by October’s end will still be only 7 degrees distant. Saturn’s brightness stays constant during the month at +0.5 whilst its angular size drops slightly from 15.9 to 15.4 arc seconds. However, the rings are almost at their most open at 26 degrees from edge on and so still make a magnificent sight. Some 20 degrees above the southwestern horizon at the start of October an hour after sunset it will fall then to just 10 degrees by month’s end. This is really our last chance to observe it this apparition.
  • MercuryMercury is just past the peak of its best morning apparition, shining at magnitude -0.8 some 8 degrees above the eastern horizon 45 minutes before sunrise. On the 11th, at magnitude -1.1 it will lie just 0.8 degrees to the left of Jupiter. Its disk then has an angular diameter of 5 arc seconds. Mercury will appear lower each morning becoming lost in the Sun’s glare by mid month as it moves towards superior conjunction with the Sun on the 27th.
  • MarsMars, lying in Sagittarius, reaches its lowest declination (-25 degrees) on October 3rd and so will be seen some 9 degrees above the south-southwestern horizon as twilight ends. Fading from magnitude +0.1 to +0.4 during October, with a disk shrinking to just 8 arc seconds across during the month it will only appear as a featureless salmon-pink object. It starts the month to the lower left of the Lagoon Nebula, M8, and, on the 6th, passes just south of the top star making up the ‘Teapot’, Lamda Sagittarii. In the last two weeks of October it passes over the Teapot’s handle as it moves eastwards across the heavens. It lies closest to the Sun on the 29th.
  • VenusVenus can be viewed low in the southwest after sunset, starting the month in Libra with a magnitude of -3.9. On the 17th, it passes into Scorpius and then, on the 25th, into Ophiuchus. As it does so it will rise a little higher in the sky. But, despite its brightness, binoculars might well be needed to spot it, but please do not use them until after the Sun has set. During the month, its angular size increases from 12 to 14 arc seconds whilst the illuminated percentage of its disk falls from 86 percent to 78 percent. These two factors compensate each other so it brightness stays virtually constant. On the 5th, Venus passes just below the wide double star Alpha Librae whilst on the 20th it passes close to Delta Scorpii which forms part of the scorpion’s head.
  • Southern Hemisphere

    Claire Bretherton from the Space Place Carter Observatory in New Zealand speaks about the Southern hemisphere night sky during October 2016.

    Kia ora, and welcome to the October Jodcast from Carter Observatory in Wellington, New Zealand.

    October is a good time to look out for the zodiacal light, seen as a triangular glow in the west after sunset in a clear, dark sky. It is caused by light reflecting off dust along the plane of our solar system. This plane is marked by the ecliptic, the apparent path of the Sun across the sky, which runs through the constellations of the zodiac. At this time of year the ecliptic makes a steep angle with the horizon, making the zodiacal light easier to observe.

    As our nights are getting lighter and our days warmer our winter zodiac constellation of Scorpius/ te Matau a Maui drops down towards the horizon, taking cream-coloured Saturn with it. Saturn sits to the right of orange Antares, and with its 29.5 year orbit around the Sun, moves very little against the background sky. The pair set shortly before 11pm by the end of the month.

    In sharp contrast, Venus, with its 225 day orbit, moves quickly eastwards against the background stars, appearing higher and higher in the western evening sky. By the end of the month it passes between Saturn and Antares, setting over 3 hours after the Sun.

    Red Mars is higher still and continues to hold its position well this month, moving through the constellation ofSagittarius and setting after around 2 am. As we move away from Mars on our inner orbit, it is slowly slipping down the sky, and gradually becoming fainter, but it will remain in our evening skies well into the New Year.

    If you have a good pair of binoculars or a small telescope, you might want to look for another planet this month. Uranus, the second most distant planet in the Solar System, reaches opposition on Saturday 15th. This is when Uranus lies on the opposite side of Earth to the Sun, reaching its highest point in our skies at around midnight. It is also around this time that Earth and Uranus are at their closest, although this won’t make too muchdifference to the planet’s brightness from our point of view.

    Uranus will be above the horizon for much of the night, shining at magnitude 5.7 in the constellation of Pisces the fishes. On a very dark, clear night it may just be possible to glimpse Uranus with the naked eye, but a full Moon close to the time of opposition will make this impossible at that time. Better to look at either the start or end of the month, closer to the new moon. With binoculars, however, Uranus should be relatively easy to spot, as long as you know where to look, although it will appear as just a star like point of light without the use of a telescope.

    A little to the north of Pisces is the constellation of Pegasus, the winged horse, which appears to leap across the northern horizon in our evening sky. Pegasus is easy to spot by the Great Square of stars that makes up his body.

    The brightest star in the constellation is the reddish star Epsilon Pegasi, marking the horse’s muzzle. This star is commonly known as Enif, deriving from the Arabic word for nose. Epsilon Pegasi is an orange supergiant, around 12 times the mass of the Sun , and with a radius some 185 times larger.

    Nearby (and visible in the same binocular field of view) is the globular cluster M15, one of the oldest and best know star clusters in the sky, with an estimated age of around 12 billion years. The cluster is located around 34,000 light years away and measures 175 light years across. M15 is probably the most densely packed globular cluster in our galaxy, with half of its mass concentrated within 10 light years of the centre. It has been suggested that this massive concentration of stars may be caused by a rare type of supermassive Black Hole in the cluster’s core.

    With binoculars M15 will appear as a fuzzy star, whilst a medium sized or larger telescope will reveal individual stars, particularly towards the outer regions, appearing as chains and streams radiating out from the core.

    M15 also contains the planetary nebula Pease 1, the first to be found within a globular cluster. At magnitude 15.5, this is a faint object, and a telescope with an aperture of at least 300mm would be needed to observe it.

    The star at the bottom right of the Great Square of Pegasus is in fact Alpha Andromodae, or Alpheratz, the brightest star in the constellation of Andromeda. Located some 97 light years from Earth it is a spectroscopic binary star whose two components orbit each other in just 100 days.

    Alpheratz is a great starting point to star hop to the great galaxy in Andromeda, or M31. The nearest large spiral galaxy to our own, M31 makes a rare appearance in our southern hemisphere skies at this time of year, but you’ll need a good, dark sky and a clear view of the northern horizon to spot it. The further north you go, the better your chances of finding it.

    From Alpheratz look for two chains of stars extending out to the east. Hop along the uppermost, and brightest, of these chains past Delta Andromedae to Mirach (Beta Andromedae), then turn sharp right and head down to Mu Andromedae before jumping on the same distance again to find the galaxy.

    The Andromeda galaxy covers an area around 6 times the diameter of the full moon, but only the brighter central region is easily visible to the naked eye, or with binoculars or a small telescope.

    At 2.5 million light years away, and magnitude 3.4, it is the most distant object easily visible with the naked eye. Andromeda is thought to contain around one trillion stars, well over twice the number estimated in our own Milky Way. Some recent studies, however, have suggested that the Milky Way may contain more dark matter than Andromeda, giving the two galaxies a similar mass.

    M31 is approaching the Milky Way at 110 km/s and is expected to collide and merge with our Galaxy in around 4 billionyears.

    A little higher and towards the east, the Triangulum galaxy or M33 is better placed in our skies. At around 3 million light years from Earth and shining at magnitude 5.7 it is just at the limit of naked eye visibility under excellent conditions, making it one of the most distant objects able to be glimpsed unaided. With the mass of 10s of billions of Suns, M33 is the third largest member of the local group. Like the Andromeda galaxy, it is also approaching us, at around 100,000 kilometres per hour.

    To find M33, head back from Andromeda towards Mirach and then continue a similar distance to the other side. Whilst M33 with the naked eye is a challenge, it is easily observable in a pair of binoculars.

    The most striking feature of the Triangulum Galaxy is a massive region of star formation, known as NGC604, which can be seen with a small telescope. NGC604 is 100 times larger than the Orion Nebula and contains over 200 hot, massive blue stars formed just 3 million years ago. In fact, if it were at the same distance as the Orion Nebula, only the Moon would be brighter in the night time sky.

    Of course there are 2 galaxies that are always visible in our night sky, the Large and Small Magellanic clouds, which are circumpolar here in New Zealand. To find the Magellanic Clouds, first look for the bright star Canopus, twinkling colourfully, low in the southeast. The Magellanic clouds appear as two small smudges of light above it, they are irregular dwarf galaxies that neighbour our own. Whilst these galaxies are much smaller than the Milky Way, they still contain hundreds of millions of stars.

    The Large Magellanic Cloud, or LMC, is the lower of the two and is located 160,000 light years away. Through binoculars or a small telescope you may be able to spot a number of young star clusters visible as small patches of light. The LMC also contains a massive star formation region, one of the largest and brightest known, called the Tarantula nebula or 30 Doradus. Spanning around 600 light years across, and covering 13 arcminutes in the sky,the Tarantula nebula contains over 800,000 stars and protostars and is the most active starburst region identified within our local group of galaxies. If it were placed at the same distance as the Orion Nebula it would be so bright that it would cast a shadow here on Earth.

    The star formation activity within the Tarantula nebula began a few tens of millions of years ago, and some of the largest and brightest stars born within this region have already reached the ends of their short lives. In February 1987 supernova SN1987A was discovered in the outskirts of the Tarantula nebula by astronomers at Las Campanas Observatory in Chile, and independently by prolific amateur astronomer Albert Jones here in New Zealand. This supernova was the closest since the invention of the telescope just over 400 years ago and provided a unique opportunity for astronomers to study such an event in unprecedented detail. Reaching a peak magnitude of around 3, SN1987A was easily bright enough to spot with the naked eye.

    Smaller and more distant, at around 200,000 light years, is the Small Magellanic Cloud, or SMC. To the top-right of this galaxy you may spot a faint fuzzy ‘star’. This object is not actually associated with the SMC but is a beautiful globular cluster called 47 Tucanae, or NGC 104, and is actually located just a tenth of the distance away on the outskirts of our own galaxy. At magnitude 4.9 it is the second brightest globular cluster in the sky, after Omega Centauri, and can be easily seen with the naked eye. With a binoculars or a small telescope it is a wonderful sight, revealing a densely packed central core, whilst a larger telescope will start to resolve some of its millions of ancient stars.

    Wishing you clear skies and happy galaxy hunting from the team hear at Space Place at Carter Observatory