The night sky for October 2015

For the last few months, here in New Zealand we have been looking a lot at the stars on our flag. This is the first time in history that all New Zealanders will have a say in the design of a new NZ flag. Our current flag was designed in 1859 for ships and adopted as the national flag in 1902, and features the Union Jack and the Southern Cross.

Click here to listen to the October 2015 Jodcast. This is a transcript of the Southern Hemisphere Night Sky. Credits due to the lovely Becky Bateman from SpacePlace – who came up with the idea to have a starry talk about flags. 

So we will start our journey of the October Night sky pointing at the Southern Cross, or Crux as it is officially named by the International Astronomical Union. We will follow the Milky Way as usual, looking at what other wonderful things we can see there. On the way across the sky we will talk about the third brightest, second brightest and the brightest star in the sky and where to find them. We will discover luminous and massive stars along the way. We also look at flags of the world that have stars, moons and Suns and finally wander away with the planets in the morning sky.

Why don’t you just 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.

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Alpha Centauri – our closest neighbour, only (roughly) 4.25 light years away.

The Southern Cross

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.

Our most famous constellation is also the smallest of the 88 constellations of the sky, covering a patch of only 68 square degrees. Although about five thousand years ago it was completely visible at midnight during spring, even from mid latitudes in the Northern Hemisphere, the Earth’s precession gradually brought it beneath the northern line. The General Precession, as it is known in astronomy, is the wobble of the Earth about its axis. This wobble will also bring into view different polar stars. The circuit is completed in 26,000 years. Because of the general precession, the Southern Cross it is only circumpolar now to those living south of 34 degrees latitude south, although it can be seen up to below 26 degrees latitude north (the latitude of Miami).

Circumpolar means it never sets nor rises but travels the sky in a big circle.

The Southern Cross was originally part of the constellation of Centaurus. Augustin Royer established it as a constellation in 1679. The Southern Cross is a true beacon of the Southern Hemisphere. It is very easy to find directions by it even though it’s not indicating the south celestial pole directly. Personally, I find it easier to find my way here in the Southern Hemisphere with the help of the Southern Cross than I did in the Northern Hemisphere looking for Polaris. 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. Opposite the Southern Cross, also within the Milky Way and circumpolar to the Northern Hemisphere, is Cassiopeia, the queen whose stars form a W shape in the sky.

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 reveals stars that shine in many colours and they are very beautiful.

The Diamond Cross

Lower in the sky than the Southern Cross in October is the Diamond Cross, an asterism in the southern constellation of Carina. The patterns that people make of the stars are called asterisms. In contrast, constellations are set areas or patches of the sky, just like countries on Earth, which take their names from asterisms. Asterisms are dot-to-dot pictures, fanciful patterns on the celestial firmament. So the diamond cross asterism, just like its name describes it, looks like a diamond. 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.

Winner of Earth & Space Category and Overall Winner of Astronomy Photographer of the Year 2013
Southern Cross, Diamond Cross, Magellanic Clouds, Canopus, False Cross, and the MILKY WAY KIWI – Mark Gee’s famous Winner of Earth & Space Category and Overall Winner of Astronomy Photographer of the Year 2013

Eta Carinae

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. Its size is about 250 times the size of the Sun. Colliding powerful winds form a bow shock – similar to the sonic boom from a supersonic airplane – that then heats the gas between the stars. The two stars travel around each other along highly elliptical paths during their five-and-a-half-year long orbit.

The Chandra X-ray Observatory discovered that depending on where each star is on its oval-shaped trajectory, the distance between them changes by a factor of twenty. Stars like Eta Carinae are just a few floating among the rest of 400 billion that make our galaxy. At about 7500 light-years from Earth, it was first recorded as a 4th magnitude star. It brightened considerably over the period 1837 to 1856 in an event known as the Great Eruption.

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Eta Carinae – NASA

Eta Carinae became the second brightest star in the sky in 1843 before fading to well below naked eye visibility. 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. I remember how the silence of the night felt heavy and dense around me whilst my eye was stuck to the telescope. I had to use peripheral vision, with the help of my rod cells from the retina to see it properly. The time almost stopped for me whilst I was basking in the glory of the light I was receiving from Eta Carinae.  What a night!

The Cat Star

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 was the famous navigator of the golden fleece ship, Argo Navis. In Māori 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. A yellow star, Canopus is 13 000 times the Sun’s brightness and 300 light years away.



The False Cross

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 declination as the stars of Crux. The story goes here in New Zealand that whoever followed the False Cross ended up in Australia… If that were true then Australia would have had perhaps the false cross on her flag. Instead, it has the  Southern Cross. However the Australian flag also sports a fifth star, Epsilon Crucis, as well as the big star of the commonwealth placed just underneath the Union Jack.

australian_flag_pictures

The Southern Hemisphere teems with astronomy related national flags. The smallest of the 88 constellations is found on state flags, provinces flags, company logos and many more. Australia, New Zealand, Niue, Tokelau, Papua New Guinea, Samoa, and in the South American Continent Santa Cruz (in Argentina), Antarctica and Mercosur (South American Common Market) and the flags flown by Argentina and Chile in Antarctica have the Southern Cross on it.

The night sky from the flag of Brazil

Whilst most of these countries fly the Southern Cross, I believe that the most spectacular flag astronomically speaking is the flag of Brazil, a true star chart. It is in fact a sky chart over Brazil’s night sky on November 15 when the Republic of Brazil was proclaimed.  There are 21 stars on the chart representing the states of Brazil, including the stars of the Southern Cross, Canopus, Procyon and Sirius, Sigma Octantis, Spica and also Scorpius which is where I want to go next in our journey.

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“Flag of Brazil (dimensions)” by Tonyjeff, based on national symbol.

Scorpius

ScorpiusScorpius – 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 Māori legend it will continue to do so all throughout October. Rehua the Māori 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. Imagine this in the desert of Sahara at night. Once the bottom of a sea, the desert now teems with creatures like the scorpion and its name made it to the stars, given probably by the other great navigators by the stars, the ancient caravan leaders.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 Māori navigators.

Antares the brightest star in Scorpius, is a red giant star: 600 light years* away and 19 000 times brighter than the Sun.  Red giants are dying stars; wringing the last of the thermonuclear energy from their cores.  Massive ones like Antares end in a spectacular supernova explosion, although it is believed that nothing will compare to the explosion from Eta Carinae, which is expected to end as a hypernova in the near (astronomical) future.

Above and right of the fish hook ‘the teapot’, made by the brightest stars of Sagittarius, is upside down in our Southern Hemisphere view.

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

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The furthest place a flag has ever been planted by humans. Directly. By hand. Okay glove of the spacesuit.

The moon is just below Saturn on the 16th and well to its right on the 17th. As we have arrived to the Moon, please note that this is also on some countries’ flags. When the Turks conquered Constantinople (now Istanbul) in 1453 they adopted its flag also adopting the crescent flag into Islam. Algeria, Azerbaijan, Brunei, union of the Comoros, Laos, Libya, Malaysia, Maldives, Mauritania, Pakistan, Palau (which has a full Moon on its flag), Singapore, Tunisia, Turkey, Turkmenistan, Uzbekistan, Western Sahara, South Carolina, and Northern Cyprus they all have the moon on their flags. Whereas the US has their flag of a star spangled banner on the Moon. This is the furthest place that a flag was taken by humans.

The Milky Way Kiwi

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The Spectacular Milky Way Kiwi – by only_eats_plankton

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. More than ten years ago astrophotographers from New Zealand were taking snapshots of the night sky. One of them looked at the pictures and realised that the dark patch known in the Northern Hemisphere as the Dark Horse, being upside down here, looked just like a great galactic kiwi bird. But as I realised later while traveling, you either have to be from New Zealand or have friends in New Zealand to know what a kiwi looks like. The Milky Way Kiwi is my absolute favourite object in the sky and I once saw it with the naked eye from Lake Tekapo in the South Island.

The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the Sun is just one.  The thick hub of the galaxy, 26 000 light years away, is in Sagittarius. The actual centre, with a black hole four million times the Sun’s mass, is hidden by dust clouds in space which make interesting shapes like our Milky Way’s kiwi. The direction of the black hole is right on the top of the head of the Milky Way kiwi, just like a jewel on a crown. At just 26,000 light years from Earth, Saggitarius A* is one of very few black holes in the universe where we can actually witness the flow of matter nearby. The very large telescope in Chile has some interesting stories to tell about that.

The Dog Star and neigbours

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. This does not mean that ‘dogs are brighter than cats‘ in general, as Donald James said, but just that the dog (star) is closer to us, at about 8 light years distance.

But it seems that this dog’s yard is the home of both the brightest naked eye star and also of the largest known star. That is VY Canis Majoris; a red hypergiant star in the Canis Major constellation – our Big Dog. The stars is located about 5,000 light-years from Earth. Its upper size its believed to be  more than 1,540 times the size of the Sun. Placed in our Solar System, its surface would extend out past the orbit of Saturn.

That’s the biggest star that we know of, but the Milky way probably has dozens of stars that are even larger, obscured by gas and dust so we can’t see them. 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.

VY Canis Majoris
The biggest star ever known

The ‘Empty’ Sky

With the Milky Way descending from the heavens, the sky looks almost empty on the other side apart of a few smudges of light and some bright stars. But that means nothing. When the Hubble Space Telescope turned toward a part of the sky that was carefully selected to be as empty of stars as possible. It took the famous Hubble Ultra deep sky picture, the deepest portrait of the visible universe ever achieved by humankind. Where our eye sees only empty blackness, Hubble reveals a universe teeming with galaxies.

A wide-field image of the region of the sky around the constellation of Fornax, constructed from the data from Digitized Sky Survey 2. The field of view is approximately 1.94 degrees x 1.65 degrees.
A wide-field image of the region of the sky around the constellation of Fornax, constructed from the data from Digitized Sky Survey 2. The field of view is approximately 1.94 degrees x 1.65 degrees.

Still, with the naked eye, its almost empty: you can see 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.

To the 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.  They are galaxies like our Milky Way but much smaller. The Large Cloud is about 5% the mass of our Galaxy and the small one 3%. That is still many billions of stars in each. The LMC is around 160 000 light years way; the SMC around 200 000 l.y. And it is believed that the LMC is the home of the most massive star known, with the mundane name of R136a1 There’s some controversy, but it might contain as much as 265 times the mass of the Sun.

On moonless evenings in a dark rural sky the Zodiacal Light is visible in the west.  It looks like late twilight. One sees a faint broad column of light passing through Libra. It is Sunlight reflecting off meteoric dust in the plane of the solar system. The dust may have come from a big comet, many centuries ago.

Flags and 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. Mars has a flag too although according to the Outer Space Treaty, no country can claim it the flag was created as a symbol of the vision for the “future history” of Mars in which the planet is transformed from red, to green, and then blue like the Earth. It flies the colours red, green and blue and it symbolises liberty as every tricolour flag does.

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.

The Sun is rising in the morning for most of us and with it a new day begins. There are many countries that have the Sun on their flags. I want to mention only one, the flag of Tuktoyaktuk, located in the Northwest Territories (Canada). What’s so special about this flag? It harbours the midnight Sun, something I always dreamed to see.

The midnight Sun on the Tuktoyaktuk flag

Flags are a reminder of things that matter to us. Their symbolism is helping us focus our attention like a beacon in the wilderness. Beacons help guide navigators to their destinations, just like the stars can do. May the stars be with you!

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.

Read more:

NASA Chandra – Sag*A
The Flag of Mars
The Behemoth Eta Carinae: A Repeat Offender
What is the biggest star in the Universe?
Chandra Eta Carinae

Hubble’s Ultra Deep Field
NZ Flag Consideration Project
NZ Flag, your chance to decide
Flags of the Night Sky Book – Amazon Link
The Origins of NZ Flag