Listen to the February 2016 starry sky here, under the Jodcast.
Getting to know the southern sky is for ever a wonderfully strange experience. In any new place that I visit I always feel grateful for landmarks. On Earth, I am looking for trees and buildings and mountains, in the sky I always look for the brightest stars. Here in New Zealand, there are places and times when the light of the individual stars is lost in the haze of the Milky Way as if a blanket of tiny lights is covering the Earth at night.
Not this time!
This time of the year we can only see the brightest stars in the evening sky.
The Sun’s winter wife, Hine Takurua/Sirius is the brightest star in the sky, reaching the sky’s peak at nightfall, to the north of the sky’s highest point, the Zenith.
Left of Takurua are the stars of Tautoru or, as we know them from the Northern Hemisphere, Orion’s Belt: Alnilam, Alnitak and Mintaka. Mintaka is precisely located on the celestial equator, which is the projection of Earth’s equator in the sky. This means Mintaka rises perfectly due East and sets perfectly due West, being a great companion for celestial navigation.
To Kiwis, Tautoru makes the bottom of ‘The Pot’. There are a few pots and pans in the New Zealand’s sky … and the cuisine here is delicious, so pots and pans figure strongly in New Zealand’s astronomy. One important pot contains Orion’s belt and its sword is the handle of the pot.
Above the pot, or Tautoru in Māori, at a distance somewhere between 700 and 1700 light years from Earth, is the glistening blue giant Puanga or Rigel, another very bright star. Actually Rigel is the seventh brightest star in the sky. “Only” 10 million years old, it is still burning hot at 12,000 degrees, in the constellation of Orion.
What is a constellation? – reloaded
Modern constellations are only patches in the sky, similar to countries on Earth, although they have kept the names given long ago to the asterisms that inspired their creation. There are 88 such patches covering the entire sky. One of them is Orion. The dot to dot shapes that we make from stars, are called asterisms. Asterisms can be inside of a constellation, like The Pot is inside Orion, or they can stretch over many constellations like the Māori Waka o Tama Rereti stretches across 270 degrees over the Milky Way in November. Another example is the ancient asterism of Argo Navis, which today is made of Carina, Puppis and Vela.
By convention, the brightness of the stars in a constellation is noted with the letters of the Greek alphabet.
Alpha for the brightest, beta for the second brightest and so on. And just like for countries on Earth, if the people of New Zealand are called New Zealanders, according to this convention, the name of the specific star identified by a Greek letter is followed by the genitive form of its parent constellation’s Latin name. For instance Alpha Orionis, means the brightest star in Orion.
This is something that astronomer Johann Bayer invented long ago to help him map the stars. But as there are always exceptions, here is one: although Rigel is the brightest star in Orion, its Bayer designation is Beta Orionis (Beta Ori, Beta Orionis), which means that when Bayer was compiling his famous atlas Uranometria in 1603, Rigel was not the brightest star in Orion, but the second brightest.
Many years have passed since then but Rigel has kept the name of Beta, even though is now officially the brightest star in Orion. Sometimes, historical conventions or events are more important in the grand scheme of things. However, for me is very important to understand why we stick to them even when they don’t make too much sense.
In stellar navigation, Rigel is also a significant star. Old records name it marinus aster, Latin for maritime star. No surprises why that was, since Rigel is bright, easily located and equatorial, which means it near the celestial equator, the projection of our own Equator in the sky and this means it is visible all around the world’s oceans. Its declination (the celestial equivalent of latitude) is minus 8 degrees (that would be like saying 8 degrees latitude south) so it cannot be seen from latitudes North of 82 degrees, that is about 8 degrees from the North Pole. Splendour and honours were attributed to the lot born under Rigel, according to the ancients.
Opposite Rigel, on the other side of Orion’s belt (more precisely below it, as seen from Wellington New Zealand), Pūtārā/ Betelgeuse, a shining red giant, or more precisely a supergiant, is the ninth brightest star in the sky. Betelgeuse is the second brightest star in Orion, floating in space about 600 light years away from us. Betelgeuse is a mistranslation of an unpronounceable (for me) Arabic name, meaning the armpit of the Central One or, according to some other people, Orion’s hand. It is also part of the famous winter triangle of the Northern Hemisphere. For the ancients, being born under Betelgeuse brought fortune, martial honours, wealth and other kingly attributes.
Betelgeuse is visible to virtually every inhabited region of the globe, except for a few research stations in Antarctica at latitudes south of 82 degrees, that is within around 8 degrees from the South Pole. That is because the declination of Betelgeuse in the sky is almost 8 degrees. If Betelgeuse would be a city on Earth it would be located at 8 degrees latitude North. Both “cities” of Betelgeuse and Rigel would share the same meridian, which in the sky is called Right Ascension.
Even though it is just a tad younger than Rigel, at about 8.5 million years old, Betelgeuse is a dying star approaching supernova, which is estimated to happen within the next 100,000 years.
It’s end is near.
Betelgeuse is also known as Alpha Orionis (although it is now the second brightest in the constellation, after Rigel), and it was indeed noted as a much brighter star than what is now observable.
Betelgeuse together with the two dogs, Sirius the big dog and, on the other side of the Milky Way, Procyon, the small dog, make a beautiful triangle, which obviously from New Zealand is upside down but still pointing at Taumata Kūkū, the Hyades, which are forming a mathematical ‘less-than’ (<) shape in the north western sky as seen from Wellington.
The Shining Ones
Lower down, Te Tāwhiti – the Shining Ones (or the Pleiades star cluster) – prepare for their trip to the underworld, soon to disappear behind the Sun. We will not be seeing them from March until the end of June when they will reappear just before the Sunrise, but they will be called a different name then: Matariki. Unlike the Europeans, who once we name a pattern of stars we keep it at all times of the year, the Southern Hemisphere is very fluid in this respect and I have learned that the Māori have different names for the same stars at different times of the year. Mostly these combinations come in threes. I have wondered why, and then realised that as the Earth goes around the Sun, the sky visibly appears to change only from season to season (or almost every three months if you wish). That is, if you compare it at the same time of the night throughout the year. So for the Māori, making different combinations in the sky according to the season they were in, was a great way to lock this knowledge into a different form of a calendar.
In fact if you watch the stars in the sky all night long, you will see that they behave just like the Sun: they will drift westwards throughout the night. Of course they don’t, it’s the Earth spinning around. But unlike the Sun, if you watch carefully, you will notice that every night, the same stars, if you look at them at the exact same hour and minute as the previous night — and taking a visible signpost like a tree or a pole as a visual anchor — they would seem to have shifted their position also westwards, just a tiny little bit. For us on Earth, this change is very visible from month to month and especially from season to season. This is why I believe that the Māori had seasonal names for their different groupings of stars, because the same shapes are repeating every year.
Stars make a great seasonal marker, especially for their particular culture, which was created whilst navigating the seas and oceans. Compare that to landlubbers like myself who always had nature and plants and landmarks to guide ourselves by, and who often experienced four very distinct seasons. Once we had named a constellation or an asterism it’s name would stay the same throughout the year. Not so for the Māori. No wonder our cultural views of the skies are so very different. People of Old did not have such detailed information about all these celestial movements and imagined that those stars, just like the plants in the wintertime (for those who had wintertime) would go to the underworld for a while.
Perhaps that’s the reason why the reappearance of the Pleiades in the sky after a long absence is associated in many cultures with dead ancestors.
So how about the next time you look at the sky you chose a star and a signpost, like a street lamp, and watch that star at exactly the same hour of the night through the year from exactly the same observation spot. I have one such spot too and I call it the center of the Universe.
From my center of the Universe, south of the Zenith, radiant Atutahi/ Canopus is the second brightest star in the entire sky. A circumpolar star, Atutahi is an Ariki; a Chief of the Stars. Another constellation that is circumpolar to Wellington is the Southern Cross, visible from 9pm. Coincidentally the Southern Cross will be easily located roughly at the same hour, nine o’clock on what I call the grand clock of heavens. This is the area of the sky starting from around (minus) – 60 degrees declination, to which Canopus belongs as well. Now looking at the circumpolar stars from New Zealand you will notice that they seem to progress on the sky clockwise, which makes that region of the sky look even more like a clock.
The neighbours – SMC and LMC
Within the Grand Clock of the Heavens – The Large and Small Magellanic Clouds (LMC and SMC respectively) are two nearby galaxies visible to the naked eye south of the zenith. They are so prominent in the sky that the first time I spotted the Large Magellanic Cloud I simply believed it was a cirrus cloud, biased by my Northern Hemisphere image of how a galaxy should look like. Imagine my awe when I realised what I was looking at.
Part of Piscis Austrinus, Formalhaut is one of the Royal Stars, and the one that shows the secret passage to terra australis, terra incognita.
What you can’t see:
- Capricornus (Sun in Capricornus from 20th of January to 16th of February) and
- Aquarius (Sun in Aquarius from 17th of February to 11th of March)
This is the Zodiacal band, an awesome drawing by Eugene Georgiades. Since one thousand years ago, when people stopped taking precession into account, the zodiacal constellations have shifted. Yes, we are once again not what we think we are. Here is an excellent site with more details about your real star sign.
Where did the Milky Way go?
And if you wonder where our Milky Way galaxy disappears to, as we can only see a few very bright stars in the sky at the moment — well it actually hasn’t gone away! It is well known that in New Zealand there are times when the Milky Way stretches as a band of stars from North to South going through Zenith. This is one of them. At dusk (around 10 pm in New Zealand, since right now it is still summertime and the night falls very late), the band of the Milky Way comes up from the Northern Horizon where Capella is hiding below it, and then arches through Betelgeuse, Sirius, the Southern Cross and its two pointers, where it is brightest, and then descends to earth through the south. But during this time of the year we are looking towards the outskirts of the Milky Way, especially when we turn our gaze towards Orion. Thus we see less stars in the sky than when we are looking towards the center of the Milky Way.
Featured sky: Argo Navis
With the Milky Way stretching as an arch high across the sky, its brightest regions are well positioned for observing, up in the sky away from the atmospheric haze of the horizon. So let’s turn our gaze south of Zenith, to the ancient constellation of Argo Navis. Argo Navis lies entirely in the southern celestial hemisphere, which is the part of the sky south of the celestial equator, the projection of Earth’s equator in the sky. Even though it is called the Southern Celestial Hemisphere, because the sky is really huge, we can see most of it from anywhere in the world, apart of the regions of the sky covered by the Earth itself. This is the reason why we cannot see, for instance, the Big Dipper or Casiopeea from Wellington or the Southern Cross from Northern Europe. Argo Navis can be found east of Canis Major, south of Monoceros and Hydra, largely in the Milky Way covering a great extent of the sky, almost nearly 75 degrees in length and containing 829 naked eye components. Modern day astronomers have divided Argo Navis into three constellations: Karina the Keel, Puppis the Stern and Vela the Sail. No bow. The Ship is said to be moving stern-forward.
The -naut of argonaut and the Navis of Argo Navis come from the same indo-European root náu– ‘Boat or ship’. We constructed many of our modern words from this ancient termination: aeronaut, aquanaut, astronaut, cosmonaut…
Of the three constellations that made the ancient Argo, Puppis marks the stern. Inside Puppis, two less known Messier Objects, M 46 and M 47 are revealing their beauty to southern hemisphere observers. Messier 46 (also known as M 46 or NGC 2437) is an open cluster at a distance of about 5,500 light-years away. Approximately 500 stars make the young cluster, which is thought to be only around 300 million years old. That is a very young age for a star! There is also a planetary nebula, NGC 2438, near the cluster’s northern edge. But that’s no planet at all. A planetary nebula is an expanding glowing shell of ionized gas ejected from old red giant stars late in their lives as the outer layers of the star are expelled by strong stellar winds.
Messier 46 open cluster is located close by Messier 47 another open cluster, which is about one degree west in the sky, so the two fit well in a binocular or wide-angle telescope field, like two close sisters, a name to which they are often referred.
Messier 47 (Messier Object 47, M47, or NGC 2422) was considered for a while the ‘lost Messier Object’, as the coordinates indicated by Charles Messier did not reveal anything for a long time. Rediscovered independently as NGC 2422 by a Canadian astronomer T. F. Morris who had the realization that NGC 24202 and M47 were the same thing, M47 lies at a distance of about 1,600 light-years from Earth with an estimated age of about 78 million years. There are about fifty stars in this cluster.
As ancient poet Aratos said…
Sternforward Argo by the Great Dog’s tail
Is drawn; for hers is not a usual course,
But backward turned she comes, as vessels do
When sailors have transposed the crooked stern
On entering harbour; all the ship reverse,
And gliding backward on the beach it grounds.
Sternforward thus is Jason’s Argo drawn.
Canopus at its helm.
Until next time Kia Ora and Kia Kaha from the Southern Hemisphere.