<p>There's a few indicators where a source is located:</p>
<p>Direction: Radio waves are just like light waves only with longer wavelength: you have to look into the direction of the source in order to see it. Terretrial sources usually are not high up in the sky.</p>
<p>Apparent movement: Another important aspect is Earth's rotation: the sky rotates with respect to Earth's surface. Thus if the source moves with the rotation speed of Earth and remains stationary in a celestial reference frame, it is very likely a source outside of Earth - and vice versa.</p>
<p>Location / Parallax: If you have several receivers, they will disagree on the direction a signal comes from, but will agree much better the further away a source is. Celestial sources are far away enough that the direction will be (nearly) identical. The amount of disagreement, the so-called parallax gives you a geometric indicator about the distance to the source.</p>

CC BY-SA 4.0
2020-08-02T07:26:36.267Z
@a_donda https://i.sstatic.net/M2Ygf.jpg from [China Built the World’s Largest Telescope. Then Came the Tourists](https://www.wired.com/story/china-fast-worlds-largest-telescope-tourists/) also see [China Finds Phone-Wielding Tourists and Telescopes Don't Mesh](https://www.wired.com/story/china-finds-phone-wielding-tourists-and-telescopes-dont-mesh/)
uhoh
CC BY-SA 4.0
2020-07-31T07:42:58.097Z
2020-07-31T07:42:58.097Z
planetmaker
<p>To planetmaker’s excellent answer, add periodicity. This is useful if you can’t measure direction at all.</p>
<p>A signal whose intensity varies regularly over a 24-hour period is likely to be terrestrial.</p>
<p>A signal whose intensity varies regularly over a 23-hour-56-minute period is likely to be celestial.</p>
<p>For signals which (for whatever reason) can only be observed at a particular time of day - say, midnight - a 12-month period suggests “celestial” but you have to be careful because the weather has a 12-month period too, in most places.</p>

CC BY-SA 4.0
2020-08-02T07:41:06.273Z
https://en.wikipedia.org/wiki/Peryton_(astronomy)#Identification and https://www.nature.com/news/microwave-oven-blamed-for-radio-telescope-signals-1.17510
uhoh
CC BY-SA 4.0
2020-08-01T05:26:56.653Z
2020-08-01T05:26:56.653Z
Martin Kochanski
<p>How is it confirmed that a radiation source (not in visible light) is either terrestrial or celestial?</p>
<p>If in-depth explanation and/or references are possible, I would be grateful.</p>

<radiation>
Distinction between signal from terrestrial and signals from celestial sources
user30981
# Distinction between signal from terrestrial and signals from celestial sources

(Asked by: username_0 on 2020-07-31)

How is it confirmed that a radiation source (not in visible light) is either terrestrial or celestial?

If in-depth explanation and/or references are possible, I would be grateful.

**Tags:** radiation

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## 2 answers

### Answer by username_1 on 2020-07-31. Score: 3

There's a few indicators where a source is located:

Direction: Radio waves are just like light waves only with longer wavelength: you have to look into the direction of the source in order to see it. Terretrial sources usually are not high up in the sky.

Apparent movement: Another important aspect is Earth's rotation: the sky rotates with respect to Earth's surface. Thus if the source moves with the rotation speed of Earth and remains stationary in a celestial reference frame, it is very likely a source outside of Earth - and vice versa.

Location / Parallax: If you have several receivers, they will disagree on the direction a signal comes from, but will agree much better the further away a source is. Celestial sources are far away enough that the direction will be (nearly) identical. The amount of disagreement, the so-called parallax gives you a geometric indicator about the distance to the source.

> **Comments:**
> **username_2**: @a_donda https://i.sstatic.net/M2Ygf.jpg from [China Built the World’s Largest Telescope. Then Came the Tourists](https://www.wired.com/story/china-fast-worlds-largest-telescope-tourists/) also see [China Finds Phone-Wielding Tourists and Telescopes Don't Mesh](https://www.wired.com/story/china-finds-phone-wielding-tourists-and-telescopes-dont-mesh/)  

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### Answer by username_3 on 2020-08-01. Score: 2

To planetmaker’s excellent answer, add periodicity. This is useful if you can’t measure direction at all.

A signal whose intensity varies regularly over a 24-hour period is likely to be terrestrial.

A signal whose intensity varies regularly over a 23-hour-56-minute period is likely to be celestial.

For signals which (for whatever reason) can only be observed at a particular time of day - say, midnight - a 12-month period suggests “celestial” but you have to be careful because the weather has a 12-month period too, in most places.

> **Comments:**
> **username_2**: https://en.wikipedia.org/wiki/Peryton_(astronomy)#Identification and https://www.nature.com/news/microwave-oven-blamed-for-radio-telescope-signals-1.17510  

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