Increase the area

In astronomy, bigger is better. A couple of weeks ago, I mentioned plans for the ELTs (extremely large telescopes) which would be up to a 100 metres in diameter. For an optical telescope that is huge; think four standard length UK swimming pools. That's mightily impressive, even though radio astronomers have been dealing with structures that size for some time.

Even so, radio astronomers wanted more and soon found themselves at the limits of engineering. It is only possible to build a bowl so big, especially if it needs to point in any direction in the sky. To get around the problem, some clever people decided to link up the signals from different radio telescopes in a technique known as interferometry. This gives you the same resolution as a radio telescope the size of the largest separation of the telescopes in your array. So, if you have six or so telescopes spread around England, you can synthesize a telescope with a diameter of 217 km (yes, that is kilometres). At radio frequencies this just happens to give you the same resolution as the Hubble Space Telescope which is pretty cool. But is that enough for radio astronomers? Certainly not! These days there are arrays the size of Europe, the US and even bigger than the planet Earth.

Now interferometers are all well and good especially at giving great resolution, but when it comes to sensitivity - the number of levels of grey - they just don't cut it. That is because sensitivity depends on collecting area; you need a big light (or in this case radio wave) bucket, not just tiny cups well spaced out. So around the world, plans were drawn up to build a telescope with two orders of magnitude better sensitivity than anything that currently exists. The plan was imaginatively called the Square Kilometre Array (SKA) as it aims to have a collecting area of one million square metres.

At the moment there are several different designs under consideration and the actual site hasn't even been chosen. The candidates are Western Australia, South Africa, China and Argentina. You might have noticed that three of the four are at pretty much the same latitude, mainly because many of the next generation of astronomical observatories are being built in the southern hemisphere. Wherever the final site turns out to be, it will require the creation of an internationally recognized interference free zone, so will have to be in an unpopulated area.

Once built, the SKA will produce masses of science. It will study earth-like planets around other stars, do some pulsar spotting, understand magnetic fields in the space between galaxies and look at the hydrogen in galaxies in the early Universe. Unfortunately, we have to wait until at least 2015 until the first observations are made.

Posted in astro blog by Stuart on Tuesday 03rd May 2005 (23:28 UTC) | Permalink
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