<p>The following questions have got me thinking.</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/40734/7982">Is it possible to use Photolithography for telescope image sensor?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/40880/7982">Fresnel lenses for a makeshift Galilei telescope?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/27760/7982">Has anyone ever tried to make a simple telescope using ice?</a></li>
</ul>
<p>A long time ago I think I wrote an answer, or maybe just a series of comments in a different SE site. <em>I think</em> it was Biology SE, and I described ways that people used algae or mold or moss or something in a petrie dish to record a projected image; it photosynthesized faster and grew faster in the brighter areas of the projection.</p>
<p>That's too slow for recording an astronomical image from a telescope.</p>
<p>I don't think the image of the moon from an amateur telescope would be bright enough to burn itself into a small, smooth piece of wood, but I remember something about secret messages written in lemon juice that revealed themselves upon gentle warming.</p>
<p>Is there any way to permanently record a <em>nighttime</em> astronomical image without using a digital imager or photographic emulsion?</p>

CC BY-SA 4.0
2021-01-21T17:04:34.973Z
Pen, pencil and paper?
JohnHoltz
CC BY-SA 4.0
2021-01-21T20:44:56.403Z
xkcd what if has an article about using moonlight to burn (it can't happen for entropy reasons) https://what-if.xkcd.com/145/ That would also rule out the lemon juice (which works by charring)
James K
CC BY-SA 4.0
2021-01-21T22:58:01.853Z
@JamesK thanks for the reference! It cites conservation of *étendue* which is discussed in my answer to [Can a telescope ever increase the apparent luminance of an extended object?](https://astronomy.stackexchange.com/q/38395/7982). Conversely, a new answer posted to that question citing your link is sorely needed.
uhoh
CC BY-SA 4.0
2021-01-25T10:08:10.227Z
@JohnHoltz That's certainly how Galileo did it.
Michael C
CC BY-SA 4.0
2021-01-25T14:22:51.743Z
@MichaelC and how Schiaparelli documented Mars' *canali*.
uhoh
<observational-astronomy><amateur-observing><photography>
Is it possible to use something besides emulsion to directly record the image of a nighttime object using a telescope?
uhoh
# Is it possible to use something besides emulsion to directly record the image of a nighttime object using a telescope?

(Asked by: username_0 on 2021-01-21)

The following questions have got me thinking.

* [Is it possible to use Photolithography for telescope image sensor?](https://astronomy.stackexchange.com/q/40734/7982)
* [Fresnel lenses for a makeshift Galilei telescope?](https://astronomy.stackexchange.com/q/40880/7982)
* [Has anyone ever tried to make a simple telescope using ice?](https://astronomy.stackexchange.com/q/27760/7982)

A long time ago I think I wrote an answer, or maybe just a series of comments in a different SE site. *I think* it was Biology SE, and I described ways that people used algae or mold or moss or something in a petrie dish to record a projected image; it photosynthesized faster and grew faster in the brighter areas of the projection.

That's too slow for recording an astronomical image from a telescope.

I don't think the image of the moon from an amateur telescope would be bright enough to burn itself into a small, smooth piece of wood, but I remember something about secret messages written in lemon juice that revealed themselves upon gentle warming.

Is there any way to permanently record a *nighttime* astronomical image without using a digital imager or photographic emulsion?

**Tags:** observational-astronomy, amateur-observing, photography

> **Comments:**
> **username_1**: Pen, pencil and paper?  
> **username_2**: xkcd what if has an article about using moonlight to burn (it can't happen for entropy reasons) https://what-if.xkcd.com/145/ That would also rule out the lemon juice (which works by charring)  
> **username_0**: @username_2 thanks for the reference! It cites conservation of *étendue* which is discussed in my answer to [Can a telescope ever increase the apparent luminance of an extended object?](https://astronomy.stackexchange.com/q/38395/7982). Conversely, a new answer posted to that question citing your link is sorely needed.  
> **username_3**: @username_1 That's certainly how Galileo did it.  
> **username_0**: @username_3 and how Schiaparelli documented Mars' *canali*.  

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## 0 answers

