EYES ON THE NIGHT SKY: SEPTEMBER 2018

Comet Comet 21P/Giacobini-Zinner N.A.Sharp/NOAO/AURA/NSF
Date: 
1 year 7 months ago

Welcome to September’s edition of Eyes on the Night Sky. This month we will get to know the Milky Way in more detail; all you need are your eyes and a clear, dark sky. We will also cover news about planets, a stunning star cluster, a few galaxies and a possible brightening comet.

The Milky Way

Milky Way looking up at Cygnus

The Milky Way is an amazing autumn sight – look out for it during the first two weeks of September during the time of the new moon and in the third week when the waxing moon has set. You need your eyes, perhaps some binoculars but most importantly, dark skies such as the countryside, away from the town or the Elan Valley Dark Sky Park. If you don’t have a tripod to steady your binoculars, you could simply lie on a blanket on the ground and use your body as support.

Start near the Zenith - the sky right above you - and look for the dark region above the constellation of Cygnus – which is called “The Funnel Cloud Nebula” (image above) – it’s a huge funnel-shaped area,  as wide an out stretched fist - around seven degrees wide.

The Northern Coalsack lies alongside Cygnus. This molecular dust is in the region where stars are formed in our galaxy. These early forming stars (protostars) generate molecular dust and obscures visible light. In fact, there is an extremely star-rich region to the south of the Northern Coalsack  called the Cygnus OB2 star cluster that we are unable to see, due to the protostars!

The Cygnus Star Cloud is a stunning area to be studied with the unaided eyes, binoculars or a telescope with a low magnification eyepiece. Spanning seventeen degrees of sky, a dark sky will show this area to its true potential.

Next, is the Great Rift, which is unlit molecular dust that lies between the Sagittarius Arm of the Milky Way and our Solar System, located around 2.6000 light years from Earth. The Great Rift stretches from the constellations of Cygnus right down to Sagittarius.

Sagittarius section of the Milky Way

The constellation of Scutum contains a rich region of stars called the Scutum Star Cloud. Situated 6000 light years away, binoculars and averted vision will resolve this patch into individual stars. At the left of the cloud, lies the Wild Duck Cluster (M11) and can be spotted with binoculars.

If you are able to access an area with a low horizon, the Sagittarius Star Clouds are well worth studying for its intensely rich and mesmerising view through binoculars. The Smaller Sagittarius Star Cloud, also known as Open Cluster M24, which is a massive 330 light years wide and 10,000 light years from Earth.

Planet-wise, at the start of the month, Mercury rises 90 minutes from the east-northeast horizon before the Sun. It may be possible to see it with the unaided eye. This is the best time to catch this planet as it rises later throughout the month.

Venus sets around an hour after the Sun and will appear as a think crescent, being in phase. Therefore, it will only be visible in binoculars. Like Mercury, the best time to see this planet is in the first two weeks of September and it will sit low on the horizon.

Mars sets earlier in the evening this month, at 1am at the beginning of September and midnight at the end.

Saturn rises to only fourteen degrees above the horizon this month, the northern face of its rings visible. Due to the relatively low position, it may be difficult to see any great detail. Jupiter is also positioned low in the early evening sky, to the SSW and sets at 7pm at the end of the month.

Uranus will be a binocular target throughout September as it rises in the East at 9.30pm at the start of the month and 7.30pm towards the end. Use a tripod to steady the binoculars and look for a greenish disc. There is plenty of time to spot it as this planet will be present all night.

The new moon occurs on 9th September and full moon on 25th September. Earthshine may be visible around the 1st – 9th and 10th – 15th September.

We have been keeping an eye on Comet 21P/Giacobini-Zinner over the last few weeks. It is bright enough (magnitude +8 ) to be seen through 10 x 50 binoculars. It may become brighter over September, peaking at magnitude +6 .

Try to catch this comet before the moon casts too much light into the sky and watch out for moonless nights – you can use this handy darkness calendar to determine the best time to see it.

This short, periodic comet - a 6.6 year orbit around the sun - was first discovered by Michael Giaobini in Nice, France in 1900 and seen by Ernest Zinner in 1913.

21P/Giacobini-Zinner Comet

Observers will be able to track this comet until 10th September, through perihelion (orbit around the Sun). This comet has a habit of undergoing periodic outbursts, as it nears perihelion, which means it could become even brighter. The Sun’s light reacts with the icy exterior of the comet, causing sublimation and as material collapses, avalanches are created, which causes the outbursts. This recent discovery replaces the previous theory that internal geysers causes comets to erupt. Let's hope we get some clear skies to see it.

Andromeda Galaxy

Andromeda Galaxy

Explore some easy deep sky targets with the unaided eyes, binoculars or telescope. In September, our neighbouring galaxy, Andromeda (M31) is high enough to see and in areas with little or no light pollution, can be seen with the unaided eye. This spiral galaxy is situated 2.5 million light years from Earth and 220,000 light-years wide. This galaxy is known to contain around 1 trillion stars and is the largest galaxy in the Local Group. It appears as a bright ellipse in 10x50 binoculars and in telescopes of more than eight inches in aperture, dust lanes can be seen, as well as its neighbouring satellite galaxies, M32 and dwarf galaxy M110. All three galaxies can be seen through binoculars.

The Double Cluster

The Double Cluster

The Double Cluster is one of the best naked eye, binocular and telescope targets. This true pair cluster, situated between Cassiopeia and Perseus, resembles two, glowing balls of stars and has a slightly nebulous appearance through 10x50 binoculars. Through a telescope, they resolve into two glittering clusters of stars. Take some time to enjoy the contrast between the blue, hot stars and its red, cooler counterparts. In the northern hemisphere, this pair, being only a few light years apart from each other, is circumpolar - meaning it is always in the sky - every night and all night. It is situated within the Perseus arm of the Milky Way galaxy and is 7500 light years away from us.

See you next month and hope you have clear skies!