3 Observing from the Earth

By now you will have had the chance to see for yourself the importance of waiting for your eyes to adapt to the dark and the benefits of getting away from light pollution. You may also have seen the effect that binoculars have on your ability to observe fainter objects and therefore to see more objects in the sky.

But these are not the only considerations in obtaining the very best view of the stars. The Earth’s atmosphere is an equally important part of the overall optical system from object to telescope to eye or camera. On its journey from a distant object such as the Orion nebula, light may travel for hundreds or thousands of year through empty space with very little disturbance, but on the last few tens of kilometres of its journey it has to pass through the Earth’s atmosphere on its way to your eye or your telescope.

Sometimes clouds in the atmosphere can prevent us from seeing the stars at all, but even on a clear night you have probably sometimes noticed the twinkling of the stars. This is the result of non-uniformities and turbulence in the air deflecting the light slightly. Through a telescope these small deflections are magnified, causing the image to appear to shimmer and move about. The atmosphere is also never completely transparent – dust and water vapour in the air can absorb some of the light, reducing the brightness and contrast of the image.

In order to avoid interference from light pollution and the disturbances of the atmosphere almost all professional telescopes are sited well away from populated areas and high up mountains or, in the case of COAST, on a volcano, as Miquel Serra-Ricart, administrator of the Teide Observatory explains.

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INSTRUCTOR:

If you want to observe the cosmos, to see the stars, you need three things-- three fundamental things. One is to have clear skies. The second is to have very, very low light pollution. And the third one is to have a very reduced low turbulence. And the best observatory will be a column, a pillar in the centre of the horizon.

And the volcanic island are very similar to these to these pillars, to these column. Tenerife, for instance, is nearly 4,000 metres. But the island, the diameter is around 50 kilometres. So this is very similar to this column,

Here, in this observatory, we have around 85% of the days of the nights clear. The light pollution is very low because we have special rules to protect the lights of the cities and towns. For me, the more important thing is the turbulence. Here, you have this wind. This is the easy wind. And this wind stabilised the atmosphere, so some nights, we have a hole in the atmosphere. And our observations are similar to space observations, to Hubble observations. So this is the main property of our observatory, the very low, low turbulence. So to be here, to be here near the mountain is similar some nights in the space, near to the Hubble telescope.

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