<p>ds9 is a common image analysis tool used in astronomy (<a href="http://ds9.si.edu/site/Home.html" rel="nofollow noreferrer">http://ds9.si.edu/site/Home.html</a>). 
The units of surface brightness are simply detector counts per square arcsecond as that is all that can easily be deduced from an image. If you want to turn that into more physical units, you will need to know the gain of the CCD (how many photons produce each count) and you will need to make some assumptions about the wavelength of light that is producing the surface brightness of the emission <a href="http://www.astronomy.ohio-state.edu/~pogge/Ast871/Notes/Rayleighs.pdf" rel="nofollow noreferrer">this Note on Rayleighs may help</a>; if all of this emission is coming from Halpha, then this is a reasonable assumption.</p>

CC BY-SA 4.0
2018-07-29T22:19:38.727Z
2018-07-29T22:19:38.727Z
astrosnapper
<p>The value of the surface brightness is in what unit? I hope it is in Rayleighs. Is that true?</p>

CC BY-SA 4.0
2018-07-29T14:47:10.723Z
From SS9, are ihe value for surface brigtnes in  Rayleighs?
Rulx Narcisse
CC BY-SA 4.0
2018-07-29T19:20:59.023Z
What are "DS9" and "SS9"?  (I presume you're not referring to the Star Trek series.)
Keith Thompson
CC BY-SA 4.0
2018-07-31T16:56:33.710Z
SAO Image DS9. Sorry, it was a tiping errors
Rulx Narcisse
<light><ds9>
What unit is used for region Surface brightness in DS9?
Rulx Narcisse
# What unit is used for region Surface brightness in DS9?

(Asked by: username_0 on 2018-07-29)

The value of the surface brightness is in what unit? I hope it is in Rayleighs. Is that true?

**Tags:** light, ds9

> **Comments:**
> **username_0**: From SS9, are ihe value for surface brigtnes in  Rayleighs?  
> **username_1**: What are "DS9" and "SS9"?  (I presume you're not referring to the Star Trek series.)  
> **username_0**: SAO Image DS9. Sorry, it was a tiping errors  

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## 1 answers

### Answer by username_2 on 2018-07-29. Score: 4

ds9 is a common image analysis tool used in astronomy (<http://ds9.si.edu/site/Home.html>).
The units of surface brightness are simply detector counts per square arcsecond as that is all that can easily be deduced from an image. If you want to turn that into more physical units, you will need to know the gain of the CCD (how many photons produce each count) and you will need to make some assumptions about the wavelength of light that is producing the surface brightness of the emission [this Note on Rayleighs may help](http://www.astronomy.ohio-state.edu/~pogge/Ast871/Notes/Rayleighs.pdf); if all of this emission is coming from Halpha, then this is a reasonable assumption.


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