The Square Kilometre Array

[caballerodiez]

As some of you probably know, the Square Kilometre Array will become the biggest radio telescope on Earth, with a collecting area of 1 square kilometre.

The construction will start in 2021 and the first light is expected to take place in 2027. It will cover the frequencies from 50 MHz to 15 Ghz.

But what I wanted to share with you guys is a new study about how far the SKA can 'listen'.

A recent study points out that the SKA could detect extraterrestrial airport radars 200 light years away.

Source: https://www.youtube.com/watch?v=ayqyb8XCtE0

What do you guys think?

[kerbiloid]

Spoiler

Now we can see TV talk shows and soap operas about purple slugs and green squids.

 

[Vanamonde]

Since they can already coordinate distant antennas to form the equivalent of an antenna the size of the distance between them, what's the advantage to clustering units like this? 

[Bill Phil]

36 minutes ago, Vanamonde said:

Since they can already coordinate distant antennas to form the equivalent of an antenna the size of the distance between them, what's the advantage to clustering units like this? 

The Square Kilometer Array is not a clustering of units. It will be spread across thousands of kilometers with thousands of units. Essentially doing what we can already do but with more collecting area, which should improve performance.

[Shpaget]

In other words, the "square kilometer" number indicates total collecting area of the dishes, not the size of plot of land where the array is built.

Radio interferometry (using multiple, spread out antennas) increases resolution to match the theoretical big antenna of the same size as the separation between individual antennas, but it does not collect the equivalent amount of signal (sensitivity). Increasing the total collecting area is needed to get more signal.

Square kilometer array attempts to make that collecting area much bigger than anything we have at the moment, while at the same time spreading out the individual antennas thousands of kilometers to achieve the resolution. Antennas will be located in western Australia and southern Africa, so ~10000 km apart.

[Vanamonde]

As shown in the linked video, they are depicted as being "clustered" in the sense of being far closer together than dishes on opposite sides of the world. As I understand it, more area does not increase resolution. 

[Gargamel]

Moved to S&S

[Bill Phil]

6 hours ago, Vanamonde said:

As shown in the linked video, they are depicted as being "clustered" in the sense of being far closer together than dishes on opposite sides of the world. As I understand it, more area does not increase resolution. 

There will be multiple separate clusters across the planet, mainly in Australia and South Africa.

Resolution can be increased with interferometry but the "brightness" requires either a lot of time or a lot of area. That is, if you want to see a dimmer object, you need more collecting area. If you want to see a smaller object, you need more resolution.

A combination of large area and high resolution will greatly expand possible observations. And that's exactly what this array is all about.

That is, it will be able to detect both small objects (resolution) and dim objects (collecting area).

[Shpaget]

There are two clusters, but clusters are separated (one in Africa, one in Australia). In addition to those clusters, there are more dishes spread out around the clusters.

More area does increase resolution, but with modern signal analysis methods, using multiple dishes is more cost effective way to achieve resolution.

However, resolution alone is not enough. You also need the signal strength. That's where collecting area comes in.

An analogy would be a digital zoom camera. With a powerful zoom lens you can see small details far away. That's resolution, but if it is dark you may have trouble seing anything. You could try cranking up ISO (gain) but at some point you are just introducing more noise. It's too dark for a good picture. Opening up the iris will let in more light and give you a better picture, but if you've already reached the largest aperture, you're kind of stuck. Your options are either to buy a new camera that has better low light performance (with radio telescopes this won't work since they are already cutting edge and there is littke room for improvement there) or you can use a bigger lens to catch more light (more surface area for radio signal gathering).

Basically, the distance between antennas helps us see small things (resolution), while total collecting are helps us see the dark, faint objects (sensitivity).

Again sniped by Bill.