The Sky of September

Welcome to Aotearoa New Zealand where the sea surrounds us from all directions, the sky is darker than dark and the stars are very bright. The Pacific Ocean is a water-world holding the reflection of the dark night sky which comes down all the way down to the horizon, and the only signposts of the night are the patterns of the stars. We call these ASTERISMS (roughly from ‘aster’ which in Latin means star) and are made of the brightest stars in a constellation.

Constellation versus asterismDEL
The Constellation of Delphinus is everything inside the white shape. The asterism of the dolphin is marked by the light blue-green line

The modern constellations which are patches of the sky, just like countries are on Earth, take their name from the associated asterism’s image. Asterisms are dot to dot doodles – they’re the patterns on the celestial firmament.

The world is upside down

Not too many things seem familiar here in the Southern Hemisphere to those of us who started our journey from the North. Everything is upside down in the sky and the seasons are back-to-front to what we knew from home. For instance, as the autumn takes its rightful place there in September, in the Southern Hemisphere we now prepare for springtime. And there is more! The Sun here goes through the Northern part of the sky moving from right to left on the ecliptic as opposite to the southern part in the Northern hemisphere.

This makes the angle of the shadow in the morning to look just like the shadow of the other hemisphere’s evening sky.

Northern Hemisphere1
Norhtern Hemisphere’s sky. Drawing by Eugene Georgiades
Southern Hemisphere1
Southern Hemisphere’s sky. Also drawn by Eugene Georgiades

Of course here in the Southern Hemisphere the Sun still rises in the east and sets in the west. But if you just arrived here and it feels like evening in the morning, don’t let them tell you it is only jetlag.

Not just the light but also the star patterns look different here, compared with the other side of the world. I had to get over the fact that everything as I knew it is upside down in the night sky.

To really get my bearings here in the South Pacific water world, I had to unlearn everything I knew about the so called ‘Western’ night sky.

For instance, the fact that for the Polynesians, the same stars can make up to three asterisms, depending on the time of the year, came as a huge surprise.

In Europe, where the people had to survive months of snow, the ancients foresaw the future with the help of the zodiacal constellations. But the zodiacal constellations were made of the same stars, and for millennia their repetitive patterns were the best calendar our ancestors used to tell the seasons. The sky of the zodiacal band repeats itself so that each month we see the same constellations rising onto the night sky as we have seen the year before. Which is why we have twelve constellations for twelve months. This is so ingrained in our collective conscious that some people still use these constellations of the zodiac to predict the future; but isn’t that what a calendar does anyway? It peers into the future and shows us when things are going to happen.

For Polynesians these patterns changed even more often: from season to season, telling the story of their journeys. Some of their constellations (or more correctly asterisms) are huge, even stretching onto half of the sky. Some other things were constant for them too. For example, as they were roaming through the Pacific Ocean, the Polynesians observed that each island of the enormous water-world had a different zenith star. They used those stars to pinpoint these islands, to find their way back across the vastness of the ocean. And their descendants who reached furthest south, the Māori (which translates as ‘normal people’ in Polynesian language) assigned not just one zenith star, but an entire asterism-constellation to the new-found island they called Aotearoa;  the land of the long white cloud. This is the fishing hook of Maui, the Matau a Maui, whose stars coincide with the stars of what we know as Scorpius.

The legend goes that the very first navigator, Maui, landed on the South Island, which to Māori had the shape of a canoe.  From there, Maui cast his famous fish hook, the zenith constellation of New Zealand, to catch the North Island from the sea. But as the center of the Milky Way rises above the horizon, and with it the asterism of the fish hook, as seen from the South Island this would show up exactly in the North East. This is exactly the direction of the North Island of New Zealand, the island that to Māori looked like a sting ray. And as one of the modern Māori navigators, Hoturoa Barclay-Kerr was telling me, as they navigate their waka hourua, the double hull canoes, along the shore of the South Island, the curvature of the Earth makes the North Island look as if it’s popping out of the sea, as if pulled by the fish hook, which would rise in the sky lifting with it island and galaxy altogether. But even for a celestial charmed fish hook the North Island was a heavy fish. The fishing line snapped and the hook flung into the sky. As the evening falls in Aotearoa at the beginning of spring, just after sunset you can find the fish hook up stuck at the center of the Milky way at zenith. All you have to do is to lift up your head and look up.

At the beginning of springtime here the Milky Way spans the sky from north to south going through Zenith. From there, Maui’s fish hook now slowly starts to drag the Milky Way down from the sky and towards the western horizon, all night long so that night after night the center of the galaxy appears lower and lower in the evening sky. Here, in the Southern Hemisphere, we are very lucky to see the Milky Way in all its brightness and beauty. Many of the brightest stars are scattered along it or near it. Starting from North is Albireo, the beautiful orange and blue double star, in the constellation of Cygnus, also known as the Northern Cross.  On the left hand side and close to the Milky Way lies Vega, the fifth brightest star in the sky. It sits due north at dusk and sets in the late evening. Vega is 52 times brighter than the Sun and 25 light years away. On the right hand side, a celestial dolphin is flipping from the galactic river, revealing its two famous stars Sualocin (Alpha (α) Delphinus) and Rotanev (Beta (β) Delphinus), the anagram of the astronomer Nicolaus Venator who wanted never to be forgotten. Just a few degrees higher up in the sky than the dolphin, the Eagle is flying Altair towards the galactic river. Keep lifting your head up and follow the Milky Way. If you have a telescope powerful enough, you will find Pluto right there near the Teapot’s handle in Sagittarius, but at 14 magnitude you would need a large aperture telescope (of 10 inches or more) to see it, as well as great star charts to pinpoint it. If Pluto is not an easy target, the fish hook of Maui in Scorpius is home of the bright star red giant Antares or Rehua in Māori. In between Sagittarius and Scorpius there are beautiful deep sky objects and now is a great time in the southern hemisphere to hunt for them. They include the Lagoon Nebula (Messier 8), the Omega Nebula (Messier 17), also known as the Horseshoe Nebula or Swan Nebula; and the Trifid Nebula (Messier 20), a large nebula containing some very young, hot stars.

All sky 1509
Chart created by Alan Gilmore

All we need to do is follow the arch of the Milky Way if we want to find directions in the Southern Hemisphere.

Midway down the southwest sky almost opposite Altair, are ‘The Pointers’, Beta and Alpha Centauri. They point down to Crux the Southern Cross.  There are about 27 ways to find South here, and most of them involve the Southern Cross. As a circumpolar constellation, at the beginning of the spring evening sky, Crux appears almost in the 3 o’clock position on the 60 degrees declination circle.

The Jewel Box NGC 7455 – ESO VLT

Inside it, the brilliant Jewel Box, discovered by Nicolas Louis de La Caille and ‘baptised’ so by John Herschel, NGC 4755, is an open cluster of stars. At the center of it, a blue giant, a red giant, and another blue giant stars align to make the more modern asterism of the ‘traffic light’.

But nothing beats the southern sky when it comes to globular clusters.

Omega Centauri – bigger than Ben Hur

Omega centauri VLT-ESO
Omega centauri VLT-ESO

Starting with the easy one, Omega centauri (map here) it is the largest globular cluster in the Milky Way galaxy and home to about 10 million stars. At a diameter of roughly 150 light-years, it can be seen as a fuzzy star roughly near the Southern Cross. In telescopes it appears like very delicate lace and it takes skill and peripheral vision to see it but it’s worth the effort.

47 Tucane

“Globular cluster 47 Tucanae” by ESA/Hubble.

Omega Centauri’s eternal rival is a bit more clear in the telescope but still elusive to catch. 47 Tucanae globular cluster (click here for map ) hides in the constellation of the exotic bird the Toucan.

But once again the Southern Cross can help. If you imagine that Crux could also look like a giant arrowhead, you will see it pointing left to a star on the other side of its declination circle. The star in question is Achenar, lying at the end of the river Eridanus that comes all the way from Orion. We can use Achenar in many ways like this, including to find south. Our imaginary trajectory, following the arrow head, takes us in between two fuzzy clouds, two thirds from Crux towards Achenar. These are the Magellanic Clouds, the famous galaxies passing by our Milky Way.

47 Tucanae is located on the right hand side of the axis, sitting beside the Small Magellanic Cloud. But this globular cluster belongs to us, albeit on the outskirts of the Milky Way! Roughly 15,000 light years away from Earth, and 120 light years across, in ideal conditions should look almost the size of the full Moon. The astrophotographers of the southern skies have a great debate each year trying to prove which globular cluster is more beautiful than the other: Omega Centauri or 47 Tucanae.
Which side are you on?

Would you like more about September’s Night Sky? Find out here:


Listen to the September 2015 Jodcast, this includes the September Night sky for both hemispheres

I have chosen a beautiful Māori korero from the book “Song of the old tides” by Barry Brailsford  to end this story. It depicts exactly how I felt when I started learning about the southern hemisphere’s sky:

“Everything is not always as it seems. Assume nothing. Assumptions readily close the door on all that is and might be. The open mind sees beyond the breaking wave to the distant shore. It takes the longer view and sees more.“

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 and from Aotearoa New Zealand.