<p>You may be looking for the "water hole". See <a href="http://www.setileague.org/general/waterhol.htm" rel="nofollow">http://www.setileague.org/general/waterhol.htm</a>.</p>

CC BY-SA 4.0
2018-07-03T01:55:50.027Z
See my answer regarding observing the 21cm hydrogen line @1420MHz at https://astronomy.stackexchange.com/questions/26139/amateur-radioastronomy-dish-suggestions/26778#26778
IlludiumPu36
CC BY-SA 3.0
2015-01-02T11:15:44.963Z
Interesting! Yes that is more or less exactly like the summary I was hoping for. It had been optimal if there was some link to an actual background spectrum (composite, if needed) I guess but this is a great start :)
BjornW
CC BY-SA 3.0
2014-12-31T22:43:51.103Z
2014-12-31T22:43:51.103Z
ganbustein
<p>This might seem like a backwards question, but I'm interested in what wavelength to select in a (hypothetical) ground-based radio telescope observation to expect detecting as <em>little</em> as possible! :)</p>

<p>It should still be reachable from space, i.e. a wavelength with a high atmospheric absorption is probably a bad candidate.</p>

<p>I guess this could be answered by looking at a broad averaged spectrum collected by a radio telescope, and comparing against an atmospheric absorption spectrum chart.</p>

<radio-astronomy>
Which wavelength is the most quiet, for a ground-based radio telescope?
BjornW
# Which wavelength is the most quiet, for a ground-based radio telescope?

(Asked by: username_0 on 2014-12-30)

This might seem like a backwards question, but I'm interested in what wavelength to select in a (hypothetical) ground-based radio telescope observation to expect detecting as *little* as possible! :)

It should still be reachable from space, i.e. a wavelength with a high atmospheric absorption is probably a bad candidate.

I guess this could be answered by looking at a broad averaged spectrum collected by a radio telescope, and comparing against an atmospheric absorption spectrum chart.

**Tags:** radio-astronomy

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## 1 answers

### Answer by username_1 on 2014-12-31. Score: 3 | Accepted answer

You may be looking for the "water hole". See <http://www.setileague.org/general/waterhol.htm>.

> **Comments:**
> **username_0**: Interesting! Yes that is more or less exactly like the summary I was hoping for. It had been optimal if there was some link to an actual background spectrum (composite, if needed) I guess but this is a great start :)  
> **username_2**: See my answer regarding observing the 21cm hydrogen line @1420MHz at https://astronomy.stackexchange.com/questions/26139/amateur-radioastronomy-dish-suggestions/26778#26778  

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