<p>ALMA is the main example of radio-telescope located in Chile. And, what an example! the most powerful radio-telescope in the world working at millimetre and sub-millimetre frequencies. Although there are bigger single dish radio-telescopes in other places, ALMA outperforms them in general. A bigger radio-telescope has a higher sensitivity because it collects more "light" (radio waves) but its field of view is very limited. A telescope like ALMA, composed of smaller dishes, can survey a bigger area of the sky than a single dish telescope. A good resolution is achieved using <a href="https://en.wikipedia.org/wiki/Astronomical_interferometer">interferometry</a> and the sensitivity problem is compensated by the use of many dishes.</p>

<p>As pointed out in other answers there are also other interesting radio-telescopes in Chile like, for example, APEX.</p>

<p>Why there are mainly millimetre and sub-millimetre radio-telescopes in Chile? Because mm and submm wavelengths are highly absorbed by the water in the atmosphere. To get rid of this problem you have to go to very high altitudes with very low content of water vapour. This make the high plains of Chile an exceptional place to build this kind of radio-telescopes.</p>

<p>Why there are not many mid and low-frequency radio telescopes in Chile? I can only guess, but these are some reasons that I can think about:</p>

<ul>
<li>Mid and low-frequency radio-telescopes do not require exceptional atmospheric conditions. In most cases it is possible to observe through the clouds. There is no point in locating these telescopes in a remote place in Chile when you can do that closer to your place for a lower price. I think this is the main reason.</li>
<li>The astronomical community in Chile has a strong expertise in other wavelengths like optical, infra-red or mm and submm as mentioned. There is so much exceptional science to do in those areas that there was no need to push or focus in low and mid radio frequencies (at least not as much as to build their own radio-telescopes).</li>
<li>Many current radio-telescopes are improvements made on old ones like the VLA. You do not need to build new dishes but focus in improving the receivers, the data processing, etc.  </li>
<li>Future radio-telescopes like <a href="https://www.skatelescope.org/">SKA</a> will extend over a vast amount of area. They need antennas located at very big distances from West to East which made Chile alone an unsuitable option. </li>
</ul>

CC BY-SA 3.0
2015-08-12T11:55:50.947Z
2015-08-12T11:55:50.947Z
nudomarinero
<p>There are radio telescopes at many sites in the southern hemisphere.
<a href="https://en.wikipedia.org/wiki/List_of_radio_telescopes#South_America" rel="nofollow">Here's a list</a>.
Chile has a big one going in at <a href="http://at%20Llano%20de%20Chajnantor">Llano de Chajnantor</a> and several already operational. See second link for details.</p>

CC BY-SA 3.0
2015-08-12T02:40:03.927Z
2015-08-12T02:40:03.927Z
Wayfaring Stranger
<p>In northern hemisphere, we have GBT, Arecibo, Parkes, Jodrell and VLA, while
in southern hemisphere, only Australia has big radio telescopes.<br/>
ALMA is in Chile, but it is in sub-mm. </p>

<p>Is not appropriate to put big radio telescopes on the plateaus of Chile?</p>

CC BY-SA 3.0
2015-08-13T13:42:44.370Z
This question seems to be unclear and that is creating an undue number of comments. I have put it on hold for now, but if someone would care to clear up the wording, I'll be happy to reopen it.
Donald.McLean
CC BY-SA 3.0
2015-08-13T15:23:51.703Z
You list 5 telescopes. There are >200 countries. Therefore the probability is that none of them will be in Chile... There is no advantage to putting a radio telescope (as in metre wavelengths or longer, rather than sub-mm) at high altitude, since the atmosphere is transparent to radio waves. So why would you build it in Chile?
ProfRob
CC BY-SA 3.0
2015-08-14T01:42:12.697Z
@rob but you can not deny there are many big optical telescopes in the southern hemisphere, but big radio telescopes are not enough. It is not necessarily in Chile.
questionhang
CC BY-SA 3.0
2015-08-14T05:47:21.910Z
Of course there are, because the atmospheric conditions, weather, seeing, low water column etc. are ideal for optical and IR astronomy. There are no big radio telescopes in Hawai'i or the Canary Islands either. Your question has been answered.
ProfRob
<telescope><radio>
Why does the Southern hemisphere seem to be short of radio telescopes?
questionhang
# Why does the Southern hemisphere seem to be short of radio telescopes?

(Asked by: username_0 on 2015-08-12)

In northern hemisphere, we have GBT, Arecibo, Parkes, Jodrell and VLA, while
in southern hemisphere, only Australia has big radio telescopes.  
ALMA is in Chile, but it is in sub-mm.

Is not appropriate to put big radio telescopes on the plateaus of Chile?

**Tags:** telescope, radio

> **Comments:**
> **username_1**: This question seems to be unclear and that is creating an undue number of comments. I have put it on hold for now, but if someone would care to clear up the wording, I'll be happy to reopen it.  
> **username_2**: You list 5 telescopes. There are >200 countries. Therefore the probability is that none of them will be in Chile... There is no advantage to putting a radio telescope (as in metre wavelengths or longer, rather than sub-mm) at high altitude, since the atmosphere is transparent to radio waves. So why would you build it in Chile?  
> **username_0**: @rob but you can not deny there are many big optical telescopes in the southern hemisphere, but big radio telescopes are not enough. It is not necessarily in Chile.  
> **username_2**: Of course there are, because the atmospheric conditions, weather, seeing, low water column etc. are ideal for optical and IR astronomy. There are no big radio telescopes in Hawai'i or the Canary Islands either. Your question has been answered.  

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## 2 answers

### Answer by username_3 on 2015-08-12. Score: 5

ALMA is the main example of radio-telescope located in Chile. And, what an example! the most powerful radio-telescope in the world working at millimetre and sub-millimetre frequencies. Although there are bigger single dish radio-telescopes in other places, ALMA outperforms them in general. A bigger radio-telescope has a higher sensitivity because it collects more "light" (radio waves) but its field of view is very limited. A telescope like ALMA, composed of smaller dishes, can survey a bigger area of the sky than a single dish telescope. A good resolution is achieved using [interferometry](https://en.wikipedia.org/wiki/Astronomical_interferometer) and the sensitivity problem is compensated by the use of many dishes.

As pointed out in other answers there are also other interesting radio-telescopes in Chile like, for example, APEX.

Why there are mainly millimetre and sub-millimetre radio-telescopes in Chile? Because mm and submm wavelengths are highly absorbed by the water in the atmosphere. To get rid of this problem you have to go to very high altitudes with very low content of water vapour. This make the high plains of Chile an exceptional place to build this kind of radio-telescopes.

Why there are not many mid and low-frequency radio telescopes in Chile? I can only guess, but these are some reasons that I can think about:

* Mid and low-frequency radio-telescopes do not require exceptional atmospheric conditions. In most cases it is possible to observe through the clouds. There is no point in locating these telescopes in a remote place in Chile when you can do that closer to your place for a lower price. I think this is the main reason.
* The astronomical community in Chile has a strong expertise in other wavelengths like optical, infra-red or mm and submm as mentioned. There is so much exceptional science to do in those areas that there was no need to push or focus in low and mid radio frequencies (at least not as much as to build their own radio-telescopes).
* Many current radio-telescopes are improvements made on old ones like the VLA. You do not need to build new dishes but focus in improving the receivers, the data processing, etc.
* Future radio-telescopes like [SKA](https://www.skatelescope.org/) will extend over a vast amount of area. They need antennas located at very big distances from West to East which made Chile alone an unsuitable option.


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### Answer by username_4 on 2015-08-12. Score: 2

There are radio telescopes at many sites in the southern hemisphere.
[Here's a list](https://en.wikipedia.org/wiki/List_of_radio_telescopes#South_America).
Chile has a big one going in at [Llano de Chajnantor](http://at%20Llano%20de%20Chajnantor) and several already operational. See second link for details.


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