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The night sky for October 2015

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during October 2015.

The Stars

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.

The Planets

The Moon

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.


Southern Hemisphere

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.

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The Night Sky This Month is one part of the Jodcast. The full show contains the latest news, interviews with astronomers, answers to listener questions and more.

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