Stargazing in Namibia – the heavenly ‘big five’

MAIN PHOTO: Centaurus-A

By Bill Torbitt

• The Southern Cross and the two Pointers, Alpha and Beta Centauri
• The Jewel Box and Coal Sack
• Omega Centauri and 47 Tucanae
• The Tarantula Nebula and the Magellanic Clouds
• Eta Carinae

NGC6188-2

Actually in the heavens, we mean. Sadly for our northern friends, they are all clustered around the south celestial pole, so you can’t see any of them unless you visit us here. You’re very welcome, and we’ll gladly show you around.

Suppose you gazed out at about 20:30 into the Namibian sky, late May or June. In the near certainty of a clear night, what would you see? Well, if you gaze southwards, you cannot miss the Southern Cross, standing almost upright. To navigate the southern sky, we’ll imagine this as the hour hand of a great clock (which it is, of course, but a 24-hour one – by 2.30 in the morning the cross will be lying on its side, to the right).

You can always find true south by making an imaginary lengthwise extension of the cross along its axis, for about four cross lengths – there is no bright polar star in the southern hemisphere.

Startrails. Photo ©Paul van Schalkwyk

The southern skies look a little strange to a visitor from the northern hemisphere. Even the familiar constellations look upside down, and because the inhabited regions of the southern hemisphere are generally at much lower latitudes than those of Europe and North America, the paths of celestial objects rise more steeply from the horizon, causing much shorter twilights and dawns, and making the moon appear to lie on its face or back rather than the classic Man in the Moon crescent.

In Namibia with its relatively low latitude (22.5 degrees for Windhoek) we can see by turns a respectable 92% of the celestial sphere, allowing for the fact that objects within 10 degrees of the horizon can’t really be observed properly.

For deep-sky observation, the best dates are around new moon, which occur on 20 May, 19 June and 18 July this year. Let’s take a pair of good binoculars and have a look around.

To the left of the Cross is the constellation of Centauri and the two famous Pointers. The latter look about the same brightness, but one is a hundred times more distant than the other. The one further from the Cross is Alpha Centauri. This is our nearest star. It is four light years away, and like many stars, is a double, actually a triple.

Jewel box

Returning to the Cross, draw an imaginary line through the ‘top left’ stars, going downward, and you’ll encounter a beautiful, compact coloured cluster of stars aptly named the Jewel Box. Within the body of the cross is a dark cloud, visible because it totally obscures the bright starry background behind. This is the Coal Sack.

Follow an imaginary line outwards from the two ‘top, right’ stars of the Cross, and with the naked eye you may see a fuzzy patch. With your binoculars or a small telescope, this will be resolved into a massive ball of stars, with an apparent diameter larger than the full moon – it is the largest globular cluster in the sky – Omega Centauri.

Just to the right of the Cross, with a telescope, you’ll find the ghostly blue planetary nebula, not a planet at all but a shell of gas ejected from a central star.

Omega Centauri

Unfortunately at this time the sky is rather bereft of planets – Saturn is high overhead, with Mars to the west, now much less bright than at its closest approach in March. If you get up before dawn later in June, you may see Venus and Jupiter emerging from behind the sun and rising in the east as morning stars.

A rare event occurs on 5 June: a transit of Venus, when the sun, Venus and the earth are directly in line and Venus appears to transit across the disk of the sun as a black spot. This will not happen again for more than a hundred years, but Namibia will just miss the spectacle (it occurs during the night!). Our friends in Japan or Alaska will have the best view.

Above the Cross the band of the Milky Way, no longer very visible from polluted cities, sweeps majestically across the sky. It’s really a line of sight effect, marking the billions of stars in the plane of our galaxy.

Eta Carinae

So – imagining our ‘clock’ with the south celestial pole at its centre and the Cross now standing at approximately 12 – at about three o’clock you will find one of the most remarkable objects in the sky: Eta Carinae, literally a superstar, actually at least two massive stars surrounded by a nebula which looks rather like a cartoon man – hence the Homunculus Nebula, surrounded in turn by vast gas clouds. The whole system is unstable, and some time in the future will probably implode into a huge black hole, or hypernova. It’s just as well that Eta Carinae is more than 7 500 light years away from us.

Down at four and five o’clock, rather low in the sky (but if you get up before dawn you can see them rise again), are the Magellanic Clouds – dwarf galaxies, satellites of our Milky Way. The larger Magellanic Cloud hosts another of the sky’s most beautiful objects – the Tarantula Nebula, another vast, intensely luminous star cloud surrounded by filaments of gas very reminiscent of the furry legs of a tarantula. This object is 120 000 light years away – if it were as close as say the famous Orion Nebula in our galaxy (only 1 350 light years away!) it would look almost as bright as the moon. Close by the smaller Magellanic Cloud, though not a part of it, is the second-largest globular cluster in the sky – 47 Tucanae.

Sombrero Galaxy

Looking out in the nine o’clock direction – actually, turning to face the east, and looking up, following the path of the Milky Way, you will see the spectacular constellation of Scorpio, never well seen in the northern sky, and adjoining it, Sagittarius and Ophiucus. You are now looking towards the centre of the galaxy, and around this, with a small telescope, scores of globular clusters can be seen. These are giant, ancient balls of stars, surrounding the disk of our galaxy in a kind of vast halo.

Finally, turning around and facing north, you will be looking at the constellation of Virgo, in which Saturn is now situated. Best seen with a slightly larger telescope, in this one constellation there are hundreds of galaxies, many larger than our Milky Way, the so-called Local Supercluster of galaxies, ‘only’ some 50 to 100 million light years away! Keep in mind that the light by which you look at these now started its journey when dinosaurs were still roaming the earth.

Tarantula Nebula

Low down on the northern horizon, our European and American visitors will see the familiar outline of the Great Bear, pointing at nothing, of course, since the north pole star is below the horizon.

Winter 2012 edition of Travel News Namibia.

PHOTOS: Werner Rossnagel©