08 August 2014 by Stuart Dickinson

Discover the heavens with Maropeng

Escape the city limits to fully appreciate the wonders of our stellar home, the Milky Way. If you’re in Johannesburg, Maropeng’s stargazing evenings provide the perfect landscape for exploration.

The glowing arch of the Milky Way. Image courtesy of Joe Parks

From the far reaches of space, the galaxy we call home is but a pinprick of light set against the vast obsidian backdrop of the universe. Amazing, then, to think that it contains some 200-billion stars and stretches about 100 000 light years across in diameter.

In South Africa, the Milky Way is best viewed during clear winter evenings, when its glowing band seems to dominate the night sky. So why not attend the next stargazing evening at Maropeng, the official visitor centre for the Cradle of Humankind World Heritage Site, which provides the perfect landscape for exploring our night skies?

Resident astronomer Vincent Nettmann will lead a fascinating illustrated talk on this 'backbone of the sky' on 23 August, with a number of powerful telescopes available to help give stargazers the best possible view of our night sky.

Until then, here are a few incredible facts about the Milky Way to wrap your mind around.

Maropeng in the Cradle of Humankind

You are here

Our solar system occupies a tiny speck of the Milky Way – to put this in perspective (as hard as that may be), our position on the Orion Arm is about 550 parsecs from the edge of the galaxy and about 8 000 parsecs from its centre. One parsec is 30.9-trillion kilometres. Let that sink in ...

Dark matter

What you actually see of the Milky Way with your naked eye only makes up 10% of the galaxy’s mass. The other 90% constitutes an invisible halo of dark matter. We know it’s there because scientists have been able to run simulations of how fast stars orbit the centre. The heavier the mass, the faster the stars orbit. And assuming that the galaxy is only made up of matter we can see, you would get a star rotation rate much lower than what it actually is.

The centre of the Milky Way. Image courtesy of NASA

Billions of planets

It is estimated that there is at least one planet per star in the Milky Way, meaning it’s likely there are over 100-billion planets floating around in our celestial section of the universe. Planets are much harder to detect than stars as they do not emit their own light, and the only instance where we are able to detect them is when they cross between the sun and Earth, creating a dark spot.

A planet would have to exist in what scientists term the circumstellar habitable zone, or 'Goldilocks Zone' (think, ‘just right’), in order to contain water and thus, presumably, life. Based on  Kepler space mission data, there could be as many as 40-billion planets within the Milky Way orbiting sun-like stars that fall into this zone. Are we alone?

Around the galaxy in 250-million years

While Earth only takes 365 days to complete a lap around our sun, it takes our entire solar system 250-million years to orbit the black hole at the centre of the Milky Way. To put that in perspective, we’ve made about a quarter lap since the dinosaurs died. Oh, and we’re travelling at about 792 000km/h relative to the galaxy’s centre – a speed that would take you around the Earth in just over three minutes.

The Milky Way. Image courtesy of David Kingham

In myth and legend

What would an evening of stargazing be without a few romantic notions from the ancient past? Like its name suggests, old civilisations often associated the sight of the galaxy in the night sky with milk. Greek legend speaks of Hera, the wife of Zeus, who was given Zeus’s son Heracles (born to a mortal woman) to suckle. Recoiling in shock and panic, not knowing who the child was, she spilt her milk across the sky.

To many ancient Asian cultures, the Milky Way represented the luminescent bridge leading to heaven, while the Finns saw the Milky Way as a path used by birds migrating south – amazingly, this migratory theory turned out to be true as migrating birds do use the Milky Way as a guide, as do dung beetles.

It was eventually Galileo who said in 1609 that the Milky Way 'is in fact nothing but congeries of innumerable stars'.

An evening with the stars

We don’t want to reveal all the mysteries contained in our night sky, so head over to Maropeng’s stargazing evening during this last month of winter to discover more. A buffet dinner will be served before you take to the telescopes.

  • Visit the Maropeng website (www.maropeng.co.za) for more details about upcoming stargazing events, or call +27 (0)14 577 9000
  • The Maropeng Visitor Centre and the Maropeng Hotel are located just off the R563 Hekpoort Road, Sterkfontein

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