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Ian Morison tells us what we can see in the northern hemisphere night sky during October 2015.
To the south in early evening - moving over to the west as the night progresses is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is Aquilla. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle". East of Cygnus is the great square of Pegasus - adjacent to Andromeda in which lies M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia with Perseus below.
The Square of Pegasus is in the south during the evening and forms the body of the winged horse. The square is marked by 4 stars of 2nd and 3rd magnitude, with the top left hand one actually forming part of the constellation Andromeda. The sides of the square are almost 15 degrees across, about the width of a clentched fist, but it contains few stars visibe to the naked eye. If you can see 5 then you know that the sky is both dark and transparent! Three stars drop down to the right of the bottom right hand corner of the square marked by Alpha Pegasi, Markab. A brighter star Epsilon Pegasi is then a little up to the right, at 2nd magnitude the brightest star in this part of the sky. A little further up and to the right is the Globular Cluster M15. It is just too faint to be seen with the naked eye, but binoculars show it clearly as a fuzzy patch of light just to the right of a 6th magnitude star.
- Jupiter is one of the pre-dawn planets that we can observe this month. Shining at magnitude -1.7 (increasing to -1.8 during the month) it starts the month as the lowest of the pre-dawn planets and will be just 12 degrees above the eastern horizon as dawn breaks. It rises earlier as the month progresses moving upwards towards Regulus under the body of Leo, the lion, and will meet with Mars on the 17th of the month. As the Earth moves towards Jupiter, the size of Jupiter's disk increases slightly from 31.4 to 33 arc seconds so early risers should be able to easily observe the equatorial bands in the atmosphere and the four Gallilean moons as they weave their way around it.
- Saturn may be seen at the start of October, shining at magnitude +0.6 at an elevation of ~7 degrees low in the southwest about 45 minutes after sunset. As the month progresses it will become increasingly hard to spot in the evening twilight. It starts the month in eastern Libra setting around 2 hours after the Sun but passes into Scorpius on the 16th and is less than one degree above Beta Scorpii on the 26th of the month. By month's end it sets one hour after the Sun. Sadly, the atmosphere will seriously limit our view of its ~15 arc second disk and rings - now open ~24 degrees to the line of sight. We will have to wait for a few months until it can be seen in the pre-dawn sky.
- Mercury is also a pre-dawn object this month becoming visible (at magnitude +0.3) about the 11th close to a thin crescent Moon - but just 8 degrees above the horizon some 40 minutes before sunrise. Binoculars may well be needed to spot it. At this time Mercury will lie 20 degrees below Jupiter. Mercury reaches greatest elongation west on the 16th but falls back towards the Sun brightening to magnitude -1 as it does so but becoming increasingly difficult to spot.
- Mars is also a pre-dawn object starting the month almost halfway between Venus (above) and Jupiter (below) shining at magnitude +1.8 some 23 degrees above the eastern horizon an hour before sunrise. On the mornings of the 17th and 18th, Mars, then at magnitude +1.7 is less than half a degree away from magnitude -1.8 Jupiter whose disk will appear almost exactly 8 time wider than Mars. With Mar's disk still just 4 arc seconds across no details will be seen on its salmon-pink surface (unless, of course, you have access to the Hubble Telescope).
- Venus, shining initially at magnitude -4.7, will dominate the pre-dawn sky this month and will be some 30 degrees above the horizon as dawn breaks at the start of the month. On the 26th of the month it reaches greatest elongation west some 46 degrees away in angular distance from the Sun. It rises some four hours before the Sun though its disk may not appear half-lit until several days later. Venus's apparent diameter shrinks from 33 to 23 arc second during the month but at the same time the percentage of its disk which is illuminated (its phase) increases from 35 to 53 percent. As a result, the effective area reflecting the Sun's ligh remains almost constant which is why the magnitude only drops to -4.5 by month's end.
Best seen just before Third Quarter, Mons Piton is an isolated lunar mountain located in the eastern part of Mare Imbrium, south-east of the crater Plato and west of the crater Cassini. It has a diameter of 25 km and a height of 2.3 km. Its height was determined by the length of the shadow it casts. Cassini is a 57km crater that has been flooded with lava. The crater floor has then been impacted many times and holds within its borders two significant craters, Cassini A, the larger and Cassini B.
- Uranus comes into opposition on the night of the 11th/12th of October, so will be seen well this month - particularly from around opposition 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. 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.
- On October 8th and 9th The planets Venus, Mars and Jupiter will be joined by a thin crescent Moon in the eastern sky one hour before sunrise. Jupiter is closing in on Mars and it might just be possible to spot Mercury lying just above the horizon if you have a very clear view in this direction.
- Mercury may be easier to spot on October 11th 30 minutes before sunrise when, given clear skies and a low eastern horizon, you should be able to spot it just two and a half degrees to the lower left of a very thin crescent Moon.
- On October 17th, one hour before sunrise and if clear, you should be able to spot Mars (shining at magnitude +1.7) just 24 arc minutes to the left of Jupiter (magnitude -1.8). Venus, at magnitude -4.4, will then be lying 6 degrees to their upper right.
Haritina Mogosanu from the Carter Observatory in New Zealand tells us about the southern hemisphere night sky during October 2015. Click here for the full, fantastic transcript of her starrytelling.
Cats and crosses
We will start our journey of the October Night sky pointing at the Southern Cross, or Crux, and first turn South. At night south is opposite from the part of the sky known as the ecliptic, where we can see the Sun and the planets and the Moon. In the Southern Hemisphere the ecliptic goes through the northern part of the sky. Always pointing to the Southern Cross in the southwest are 'The Pointers ', Beta and Alpha Centauri, making a vertical pair at about 60 degrees declination south. Alpha Centauri, the top Pointer, is the closest naked eye star at 4.3 light years away, and it's the third brightest star in the entire sky. Beta Centauri is a blue-giant star, very hot and very luminous, hundreds of light years away. This, our most famous constellation, is also the smallest of the 88 constellations of the sky, covering a patch of only 68 square degrees. The Southern Cross is a constellation within the sky-river of the Milky Way. Being so small it fits almost perfectly in the white flow of the stars. The Southern Cross is the home of the beautiful open cluster Jewel Box or NGC 4755, which to the naked eye appears like a fuzzy patch. A telescope would reveal stars that shine in many colours and they are very beautiful. Opposite the Southern Cross, also within the milky way, and circumpolar to the Northern Hemisphere, is Cassiopeia, the W queen.
Lower in the sky than the Southern Cross in October is the Diamond Cross, an asterism in the southern constellation of Carina. Pointing towards the Milky Way at one side, adjacent to Theta Carinae, is a small open cluster visible with binoculars. Theta Carinae marks the northeastern end of the Diamond Cross asterism and it's also the brightest star in the open star cluster IC 2602. The cluster is also known as the Running Man or the Southern Pleiades, but to me it has always looked like the letter M. Also in the constellation of Carina, one of the most spectacular stars of the Southern Sky, Eta Carinae is a stellar system containing at least two stars with a combined luminosity over five million times that of the Sun. I have seen eta Carinae looking though a 40 cm Boller and Chivens telescope here at the Space Place at Carter Observatory in Wellington. Or to be more precise, I have seen the Homunculus nebula. It looked like a tiny hourglass. This is probably the most spectacular deep sky memory I have from the Southern Hemisphere.
From a star invisible to the naked eye let's jump onto the other side of the magnitude scale. Let's look at the brightest star from Carina - Canopus, the famous navigator of the golden fleece ship, Argo Navis. In Maori this star is called Atutahi and he is the Chief of all the stars in the sky. Low in the southeast, Canopus can be seen at dusk, often twinkling colourfully. It swings up into the eastern sky during the night. Canopus is a circumpolar star as seen from Wellington. Not only is Canopus the brightest star from Carina but it is also the second brightest star in the entire sky to our naked eye. As many astronomers from New Zealand call their cats Canopus, the star is also known here as The Cat Star.
Now onto our last cross, the False cross is yet another asterism in the flow of the milky way. It belongs to the constellation of vela. A bit bigger than the Southern Cross, it looks almost identical but you can tell that is the false cross because it doesn't have pointer stars pointing at it. Both the Diamond Cross and the False Cross are sometimes mistaken for the true Crux, although the False Cross has always been a worse deceiver than the Diamond Cross, because most of its stars have approximately the same declinations as the stars of Crux. The story goes here in New Zealand that whoever followed the False Cross ended up in Australia...
An astronomical menagerie
Scorpius- the official name of the constellation, which is only a patch in the sky, has an eye catching asterism in it, that looks like everything it was named after: scorpion, fish hook, dragon, and many other things. Visible from New Zealand at this time of the year you can find it if you follow the two pointers of the Southern Cross in the opposite direction. Above them, lays Triangulum Australe, below is Lupus the wolf. In front of them, the fish hook of the ancient navigator Maui, almost dragged the Milky Way down from the sky. According to the Maori legend it will continue to do so all throughout October. Rehua the Maori name for Antares, marks the bait of the hook. Above Scorpius-the fish hook is Corona Australis, the Southern Crown, a round group of stars that look like fireworks spreading apart. Or the teaspoon of the teapot, according to some who like tea. As observed from the Northern Hemisphere, the asterism is a scorpion which only goes up above the horizon for thirty degrees, which makes it seem to rather crawl around the horizon like a gigantic scorpion would do. Here in Aotearoa New Zealand because of our position on Earth, Scorpius climbs all the way up to Zenith, which is why the fishing hook was considered the zenith asterism of New Zealand by the ancient Maori navigators. Below the fish hook Saturn is currently the only planet in the evening sky. It is midway down the western sky at dusk and sets in the southwest around 10 pm mid-month. The moon is just below Saturn on the 16th and well to its right on the 17th.
Going back on the path of The Milky Way, right at the center of it, a spectacular bird guards the center of our galaxy. This is the Milky Way Kiwi, a shape made from dark dust within the milky way. Sliding down the Milky Way, towards north, the skyline meets the horizon near Vega. Vega is setting in the late evening. Vega is 50 times brighter than the Sun shining from 25 light years away. Vega is the 5th brightest star. Looking in the same direction as for Vega but in the morning, you will notice the Dog Star, Sirius. Sirius is a blue giant and the brightest star in the sky, twice as bright as Canopus, the cat star. Neighbouring it, in the constellation of Orion, Betelgeuse, in Maori Putara is a familiar star located in the shoulder of Orion. This red supergiant star has a radius of 950-1200 times the size of the Sun, and would engulf the orbit of Jupiter if placed in our Solar System.
With the Milky Way descending from the heavens, the sky looks almost empty on the other side apart of a few smidges of light and some bright stars. Nearing Zenith is Grus the famous double double asterism. Towards north, The Great Square of Pegasus the flying horse, adorns the northern horizon. Underneath it we can just barely observe the fourth galaxy visible with the naked eye: Andromeda is a dash on the blackness of the sky. Towards south, the Large and Small Clouds of Magellan, LMC and SMC, look like two misty patches of light in the southeast sky. They are easily seen by eye on a dark moonless night.
And finally, the planets
Bright planets appear in the eastern dawn sky. Brilliant silver Venus rises two hours before the Sun through October. That's around 5 a.m. at the beginning of the month. Golden Jupiter is on the dawn horizon at 6 a.m. below and right of Venus. Between the two bright planets, at the beginning of the month, are the white star Regulus and the reddish planet Mars. Beyond Mars, Jupiter moves up the dawn sky. By mid-month it is passing Mars. The pair are less than a full-moon's width apart on the morning of the 18th. Around the 26th Jupiter passes by Venus, making an eye-catching pairing of bright planets in the dawn. Jupiter and Mars are on the far side of the Sun. Jupiter is 920 million km away; Mars 345 million km. Venus is on our side of the Sun, 92 million km away on the 15th.
This concludes our jodcast for October 2015 at space place at carter observatory. As the Maori say, E whiti ana nga whetu o te Rangi (the stars are shining in the sky) Ko takoto ake nei ko Papatuanuku (whilst Mother Earth lays beneath). Kia Kaha and clear skies from the Space Place at Carter Observatory in Aotearoa New Zealand.Compiled by Ian Morison