<p>&quot;ugriz&quot; is short for U-band, G-band, R-band, I-band, and Z-band, detailed on <a href="https://en.wikipedia.org/wiki/Photometric_system" rel="nofollow noreferrer">the Wikipedia article on photometric systems</a>:
<span class="math-container">$$\begin{array}{|c|c|}
\hline \text{Band}&amp;\text{Effective Wavelength Midpoint }(\lambda_{\text{eff}})\\
\hline \text{U} &amp; \text{365 nm}\\
\hline \text{G} &amp; \sim\text{475 nm}\\
\hline \text{R} &amp; \text{658 nm}\\
\hline \text{I} &amp; \text{806 nm}\\
\hline \text{Z} &amp; \text{900 nm}\\
\hline
\end{array}$$</span>
This <span class="math-container">$ugriz$</span> system is slightly different from the <span class="math-container">$u'g'r'i'z'$</span> system; conversions can be found <a href="http://classic.sdss.org/dr4/algorithms/jeg_photometric_eq_dr1.html#usno2SDSS" rel="nofollow noreferrer">here</a>. The starting point is the same (note that <span class="math-container">$u(\text{2.5m})=u'$</span>), but there are slight vertical and horizontal shifts.</p>
<p>The differences between <span class="math-container">$ugriz$</span> and <span class="math-container">$u'g'r'i'z'$</span> are much smaller than the differences between <span class="math-container">$u'g'r'i'z'$</span> and the <span class="math-container">$UBV(RI)_C$</span> system, which was replaced by them both. This older system of filters had large overlaps and did not cover as broad a range. See Fig. 1 from <a href="https://dspace.library.uvic.ca/items/c4d2dc9e-f07f-49f3-a1d2-7e5f082dd3d4" rel="nofollow noreferrer">this thesis</a> for a comparison:</p>
<p><a href="https://i.sstatic.net/2PX2z.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2PX2z.png" alt="plot of the systems of filters mentioned above" /></a>
<br>
<sup>Plot of filters from &quot;Galactic star clusters in the u'g'r'i'z' photometric system&quot;, by James Clem Lewis.</sup></p>

CC BY-SA 4.0
2024-07-16T02:55:07.213Z
For anyone else who finds that plot useful for their own research, the link provided is now broken. The author is James Lewis Clem, and his thesis is titled "Galactic star clusters in the u'g'r'i'z' photometric system" published in 2005 at the University of Victoria. As of 2024, this [link to the pdf works](https://dspace.library.uvic.ca/items/c4d2dc9e-f07f-49f3-a1d2-7e5f082dd3d4)
user1153070
CC BY-SA 4.0
2024-07-21T14:43:41.160Z
@user1153070 Thanks for bringing that up; I've fixed the link.
HDE 226868
CC BY-SA 4.0
2016-11-07T22:43:06.383Z
2024-07-21T14:43:20.787Z
2024-07-21T14:43:20.787Z
HDE 226868
<p>While studying photometric redshifts, I came across the ugriz (or u'g'r'i'z) system for classifying magnitudes of galaxies, but I didn't find much information on the internet about how it works. </p>

<p>Can somebody explain that? Do the letters "ugriz" have any special meaning, or is its just a nomenclature?</p>

<galaxy><photometry><magnitude>
What is the ugriz magnitude system?
Renan Nobuyuki Hirayama
# What is the ugriz magnitude system?

(Asked by: username_0 on 2016-11-07)

While studying photometric redshifts, I came across the ugriz (or u'g'r'i'z) system for classifying magnitudes of galaxies, but I didn't find much information on the internet about how it works.

Can somebody explain that? Do the letters "ugriz" have any special meaning, or is its just a nomenclature?

**Tags:** galaxy, photometry, magnitude


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## 1 answers

### Answer by username_1 on 2016-11-07. Score: 11 | Accepted answer

"ugriz" is short for U-band, G-band, R-band, I-band, and Z-band, detailed on [the Wikipedia article on photometric systems](https://en.wikipedia.org/wiki/Photometric_system):
$$\begin{array}{|c|c|}
\hline \text{Band}&\text{Effective Wavelength Midpoint }(\lambda\_{\text{eff}})\\
\hline \text{U} & \text{365 nm}\\
\hline \text{G} & \sim\text{475 nm}\\
\hline \text{R} & \text{658 nm}\\
\hline \text{I} & \text{806 nm}\\
\hline \text{Z} & \text{900 nm}\\
\hline
\end{array}$$
This $ugriz$ system is slightly different from the $u'g'r'i'z'$ system; conversions can be found [here](http://classic.sdss.org/dr4/algorithms/jeg_photometric_eq_dr1.html#usno2SDSS). The starting point is the same (note that $u(\text{2.5m})=u'$), but there are slight vertical and horizontal shifts.

The differences between $ugriz$ and $u'g'r'i'z'$ are much smaller than the differences between $u'g'r'i'z'$ and the $UBV(RI)\_C$ system, which was replaced by them both. This older system of filters had large overlaps and did not cover as broad a range. See Fig. 1 from [this thesis](https://dspace.library.uvic.ca/items/c4d2dc9e-f07f-49f3-a1d2-7e5f082dd3d4) for a comparison:

[![plot of the systems of filters mentioned above](https://i.sstatic.net/2PX2z.png)](https://i.sstatic.net/2PX2z.png)
  
Plot of filters from "Galactic star clusters in the u'g'r'i'z' photometric system", by James Clem Lewis.

> **Comments:**
> **username_2**: For anyone else who finds that plot useful for their own research, the link provided is now broken. The author is James Lewis Clem, and his thesis is titled "Galactic star clusters in the u'g'r'i'z' photometric system" published in 2005 at the University of Victoria. As of 2024, this [link to the pdf works](https://dspace.library.uvic.ca/items/c4d2dc9e-f07f-49f3-a1d2-7e5f082dd3d4)  
> **username_1**: @username_2 Thanks for bringing that up; I've fixed the link.  

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