<blockquote>
  <p>How do radio telescopes gather information about visible light?</p>
</blockquote>

<p>They don't; the picture you saw all over the news was a <a href="https://en.wikipedia.org/wiki/False_color#False_color" rel="nofollow noreferrer">false color image</a>, where frequencies are shifted from the radio spectrum to the visible spectrum (blue meaning shorter radio wavelengths and red meaning longer radio wavelengths) and/or the intensities mapped to different colors (instead of just affecting the brightness as with true color images).</p>

<p>Or, to quote an old <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question20.html" rel="nofollow noreferrer">StarChild question</a>:</p>

<blockquote>
  <p>The term "false color" is used to describe what astronomers (and others) often do to images to make them more comprehensible. Long ago, when radio astronomers first started generating images of sources, they wound up with essentially images that were just shades of gray - ranging from pure black to pure white. Each shade represented the intensity of the radio emission from a particular part of the object. Radio astronomers took their shades-of-gray images and converted them to color ones by assigning red to the most intense radio emission and blue to the least intense emission recorded on the image. Intermediate colors (orange, yellow, and green) were assigned to the intermediate levels of radio intensity. Black was assigned to places in the image in which there appeared to be no radio emission.</p>
</blockquote>

CC BY-SA 4.0
2019-04-15T15:19:15.123Z
Thanks. Do we have any idea about the optical image of that black hole? Is it worth of making a new thread...?
asmani
CC BY-SA 4.0
2019-04-16T01:39:59.290Z
@Asmani there are two like that already, I think it's better for you to keep an eye on them rather than to ask again. [How does the black hole at the center of M87 look like in the visible spectrum?](https://astronomy.stackexchange.com/q/30476/7982) and also [What is the actual visual characteristics of a black hole?](https://astronomy.stackexchange.com/q/30413/7982)
uhoh
CC BY-SA 4.0
2019-04-15T14:58:51.920Z
2019-04-15T14:58:51.920Z
Glorfindel
<p>Is the first image of a black hole that was captured by the Event Horizon Telescope what would be seen with a large enough optical telescope (or with the naked eye from a proper distance of the black hole)? If so, how do radio telescopes gather information about visible light?  </p>

CC BY-SA 4.0
2019-04-15T17:25:18.470Z
You wrote 2 questions -- if you want to ask about the maximum observable distance for visible light showing the same phenomenon as this radio-image, please post that separately.
Carl Witthoft
<light><radio-telescope>
How do radio telescopes gather information about visible light?
asmani
# How do radio telescopes gather information about visible light?

(Asked by: username_0 on 2019-04-15)

Is the first image of a black hole that was captured by the Event Horizon Telescope what would be seen with a large enough optical telescope (or with the naked eye from a proper distance of the black hole)? If so, how do radio telescopes gather information about visible light?

**Tags:** light, radio-telescope
> **Comments:**
> **username_1**: You wrote 2 questions -- if you want to ask about the maximum observable distance for visible light showing the same phenomenon as this radio-image, please post that separately.  

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## 1 answers

### Answer by username_2 on 2019-04-15. Score: 4 | Accepted answer

> How do radio telescopes gather information about visible light?

They don't; the picture you saw all over the news was a [false color image](https://en.wikipedia.org/wiki/False_color#False_color), where frequencies are shifted from the radio spectrum to the visible spectrum (blue meaning shorter radio wavelengths and red meaning longer radio wavelengths) and/or the intensities mapped to different colors (instead of just affecting the brightness as with true color images).

Or, to quote an old [StarChild question](https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question20.html):

> The term "false color" is used to describe what astronomers (and others) often do to images to make them more comprehensible. Long ago, when radio astronomers first started generating images of sources, they wound up with essentially images that were just shades of gray - ranging from pure black to pure white. Each shade represented the intensity of the radio emission from a particular part of the object. Radio astronomers took their shades-of-gray images and converted them to color ones by assigning red to the most intense radio emission and blue to the least intense emission recorded on the image. Intermediate colors (orange, yellow, and green) were assigned to the intermediate levels of radio intensity. Black was assigned to places in the image in which there appeared to be no radio emission.

> **Comments:**
> **username_0**: Thanks. Do we have any idea about the optical image of that black hole? Is it worth of making a new thread...?  
> **username_3**: @Asmani there are two like that already, I think it's better for you to keep an eye on them rather than to ask again. [How does the black hole at the center of M87 look like in the visible spectrum?](https://astronomy.stackexchange.com/q/30476/7982) and also [What is the actual visual characteristics of a black hole?](https://astronomy.stackexchange.com/q/30413/7982)  

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