Colours reveal secrets

The night sky is teeming with colour if you are prepared to look for it. PHOTO: IAN GRIFFIN
The night sky is teeming with colour if you are prepared to look for it. PHOTO: IAN GRIFFIN
One of my favourite stargazing locations is Hoopers Inlet on the Otago Peninsula, writes Ian Griffin.

Ian Griffin. Photo: Otago Museum
Ian Griffin. Photo: Otago Museum
Since moving to Portobello in 2013, I've spent dozens of nights contemplating the cosmos from the shores of this magnificent natural amphitheatre.

While any clear night at Hoopers is impressive, it really comes into its own on calm, moonless evenings, especially when an aurora is glowing in the south. On such occasions, with Sandymount silhouetted, the inlet’s inky black water becomes a perfect mirror, rewarding sky-watchers lucky enough to be present with mesmerisingly memorable nocturnal vistas.

While many consider stargazing to be a monochromatic occupation, nothing could be further from the truth. The night sky is teeming with colour if you are prepared to look for it. And what's more, the colours reveal the secrets of the objects and phenomena on show.

I was reminded of this while considering a picture I took at Hoopers Inlet in November 2018 during a beautiful display of the southern lights. On that night, the Southern Cross was low in the sky, and my camera captured the colourful reflections of its major stars, blurred slightly by subtle wind-induced motions of the water.

The different hues of stars in the Southern Cross tell us something about their temperatures. Red stars are cool, while blue stars are much hotter. Gamma's orange colour means its surface temperature is a relatively cool 3500degC. The distinctly blue stars Beta and Delta are much hotter, with temperatures exceeding 20,000degC!

The colours we see when looking at the aurora can also tell us something about what is going on high in Earth's atmosphere. The glow of the southern lights is caused by interactions between particles flowing away from the sun and atoms or molecules high in our atmosphere. Green and red auroras are caused by collisions involving oxygen, while blue and purple tones indicate collisions involving nitrogen.

Next time you are out under a clear sky, take some time to contemplate the colours you see, and think about what they are telling you about our universe. You won't regret it.


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