<p>A device called a <a href="http://en.wikipedia.org/wiki/Photomultiplier" rel="nofollow">photomultiplier</a> is attached to a telescope. </p>

<ol>
<li><p>The telescope is pointed at the target star and an aperture is
closed down to avoid as much spurious light as possible, and a
reading is taken. The photomultiplier literally count the photons
hitting it.</p></li>
<li><p>Next the telescope is pointed at a well-known reference star in the
same part of the sky, the aperture is closed, and a reading is
taken.</p></li>
<li><p>Finally, the telescope is pointed at a dark part of the sky, the
aperture is again closed, and a reading taken.</p></li>
</ol>

<p>Computer software compares the data from the target star, the reference star, and the dark sky to remove as much noise from light scattered by the atmosphere as possible. It's important to know how much of the measured light is coming from the sky and subtract it from the light measured from the target.</p>

<p>Often, this same procedure is repeated with a series of filters to get the luminosity of the target star at many wavelengths. Searching for a variable star's period requires switching from target star to reference star to dark sky time after time, hour after hour, night after night.</p>

<p>I paid my way through college doing this.</p>

CC BY-SA 3.0
2014-02-07T20:16:11.967Z
2014-02-07T20:41:03.647Z
2014-02-07T20:41:03.647Z
Marc
<p>How does one measure the brightness of a star?, I did not find anything on the internet.</p>

CC BY-SA 3.0
2014-02-07T11:57:31.707Z
The technical term, you'll find more, is "magnitude": http://en.wikipedia.org/wiki/Apparent_magnitude
Gerald
CC BY-SA 3.0
2014-02-07T18:22:10.500Z
@Gerald Some clarification is needed. The OP may be looking for visual luminosity as opposed to apparent or absolute magnitude.
called2voyage
CC BY-SA 3.0
2014-02-15T15:11:59.630Z
The OP could also be asking for surface brightness. I agree, it needs to be explicitly stated what he is looking for.
astromax
<star><light><apparent-magnitude>
How is the magnitude of a star measured?
Antp
# How is the magnitude of a star measured?

(Asked by: username_0 on 2014-02-07)

How does one measure the brightness of a star?, I did not find anything on the internet.

**Tags:** star, light, apparent-magnitude
> **Comments:**
> **username_1**: The technical term, you'll find more, is "magnitude": http://en.wikipedia.org/wiki/Apparent_magnitude  
> **username_2**: @Gerald Some clarification is needed. The OP may be looking for visual luminosity as opposed to apparent or absolute magnitude.  
> **username_3**: The OP could also be asking for surface brightness. I agree, it needs to be explicitly stated what he is looking for.  

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## 1 answers

### Answer by username_4 on 2014-02-07. Score: 5 | Accepted answer

A device called a [photomultiplier](http://en.wikipedia.org/wiki/Photomultiplier) is attached to a telescope.

1. The telescope is pointed at the target star and an aperture is
   closed down to avoid as much spurious light as possible, and a
   reading is taken. The photomultiplier literally count the photons
   hitting it.
2. Next the telescope is pointed at a well-known reference star in the
   same part of the sky, the aperture is closed, and a reading is
   taken.
3. Finally, the telescope is pointed at a dark part of the sky, the
   aperture is again closed, and a reading taken.

Computer software compares the data from the target star, the reference star, and the dark sky to remove as much noise from light scattered by the atmosphere as possible. It's important to know how much of the measured light is coming from the sky and subtract it from the light measured from the target.

Often, this same procedure is repeated with a series of filters to get the luminosity of the target star at many wavelengths. Searching for a variable star's period requires switching from target star to reference star to dark sky time after time, hour after hour, night after night.

I paid my way through college doing this.


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