In the land where the stars twinkle


Picture of the Trifid Nebula, taken by SALT

Situated close to the small town of Sutherland in the middle of the Karoo is a plateau covered in telescopes. Looking from afar, it almost appears to be a mummy telescope and her babies, since one of the telescopes is significantly bigger than the rest. This telescope is SALT – the Southern African Large Telescope, and at 11m across, it is the largest optical telescope in the Southern Hemisphere.


Looking up towards the plateau where the telescopes are situated. SALT is the largest telescope, to the left.

Just another day at work

A couple of weeks ago I had the opportunity to pay a visit to SALT and spend some time with the astronomers as they carried out their night-time observations. An astronomer’s day generally starts at lunchtime, since they observe through the night. Possibly due to this, astronomers tend to run on coffee – there was great uproar when the coffee was late one evening after dinner!

This video, titled “A day in the life of an astronomer” follows one of the SALT astronomers through an average work day at SALT.

Optical vs Radio

SALT, like Hubble, is an optical telescope, which means that it can produce stunning images of space. In practice, SALT is more often used to produce spectrums of light. These give useful information such as which elements make up stars and galaxies, and can be further subdivided by astronomers to give valuable scientific information.


This is what an emission spectrum looks like. This one shows the spectrum for Xenon. Credit: Christopher Thomas [CC SA 1.0], via Wikimedia Commons

The other type of telescope is a radio telescope, which uses radio waves to build up a picture of space. Often confused with SALT, the Square Kilometre Array (SKA) is a multi radio telescope project being built in South Africa, New Zealand and Australia.

Did you know?  The average astronomer won’t be able to point out many more constellations than anyone else. Astronomers tend to have a deeper and more specific knowledge about certain stars, planets, galaxies and phenomena in space, and concentrate less on the general layout of the sky and those stars that are visible to the naked eye.

What’s the point of astronomy?

This question is apparently asked at least ten times in an astronomer’s working life. Human fascination is the main driving force behind astronomy. But in addition to this, astronomy serves as a brilliant technical training ground, resulting in human advances such as precision GPS, medical imaging, and wireless internet, along with many others. And certainly, compared to war, which is another driving force of technical advances, astronomy is a much better option. In addition to technical advances, astronomy benefits the societies it touches – sparking interest in science, and driving education.

Astronomical quirks

There’s a reason that SALT is situated so far from any big cities. Dark skies are required for optical astronomy to take place. This is so serious that the houses in Sutherland are equipped with blinds as well as curtains in order to keep the light pollution down in the immediate area. Astronomers driving up to the telescope are required to use emergency lights rather than headlights, since this creates the lowest impact – but even this can be detected by the telescope!

Because of the importance of darkness to optical astronomy, astronomers also have a different twilight to that of the average person. This occurs an hour to an hour and a half after sunset, and it is only after astronomical twilight has ended that science observations can begin.


Astronomical twilight occurs when the sun is between 12 and 18 degrees below the horizon. Credit: T W Carlson [CC BY-SA 3.0 or GFDL], via Wikimedia Commons

Astronomers also have their own vocabulary. Contrary to popular belief, seeing does not mean the action of seeing, but rather refers to a light phenomenon which results in blurry images!

In astronomer speak, seeing refers to the blurry and twinkling of light, due to turbulence in the atmosphere. Seeing makes the stars twinkle at night, but while this is beautiful to the eye, it is very bad for astronomy.

On my last night there, after some dismal weather, the sky cleared, and armed with a blanket against the remaining chill, I seated myself outside in perfect darkness to look at the stars. The seeing was bad that night – or good, to my eyes! The stars twinkled so much more brightly than I have ever seen anywhere else. And as my eyes adjusted to the darkness, it became apparent that the brightest stars can cast shadows! I’d had a great few days learning about the telescope and the amazing science that goes on there. And even if the seeing wasn’t great for the science that night, it left an impression on my memory. To me, Sutherland will forever be the land where the stars twinkle.


Sutherland sky by night. Credit: South African Tourism




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