<p>There is a difficulty with measuring magnitude: the atmosphere!  It is sometimes clear sometimes hazy and it can be very hard to know just how much light is being lost to a high layer of thin cirrostratus, or a passing puff of mist.</p>
<p>Amateurs have measured star magnitudes by the comparison technique.  This is literally comparing the star with other nearby stars of known magnitude and estimating &quot;is it brighter or less bright&quot;</p>
<p>If there are convenient nearby stars of similar magnitude, a good estimate of  0.1 magnitudes is possible by a skilled observer. There are long term sequence of the magnitude of variable stars that have been produced by this method.</p>
<p>It is harder if there is no nearby star of similar magnitude. It is easier to compare two stars in the same field of view, rather than have to move you eyes from one star to another.</p>

CC BY-SA 4.0
2022-09-25T15:57:50.943Z
2022-09-25T15:57:50.943Z
James K
<p>The easiest way to determine the magnitude of a given star is probably to use the Pogson relation. The idea is to determine the magnitude of a star knowing the magnitude of a reference star; it is thus quite easy, using a well-known reference as Vega or Sirius.</p>

<p>The Pogson relation is given by:</p>

<p>$$m_1-m_2=-2.5\ log\ \left({\frac{E_1}{E_2}}\right)$$</p>

<p>where $m_1$ and $m_2$ are the magnitudes of star 1 and star 2 (your reference star), and $E_1$ and $E_2$ brightness (that could be in arbitrary units, which is a good news for you).</p>

<p>With a CCD detector the brightness is easy to determine since it's just the flux of a pixel. You don't have to convert it in physical units (as Watt per square meter) since you have a ratio $\left({\frac{E_1}{E_2}}\right)$, so the raw intensity is enough to determine the magnitude.</p>

<p>As for any other measurement with a CCD camera, you have of course to determine the bias, dark and flat-field and to reduce your data before estimating any magnitude. The precision will depend on the number of observations performed and, as always, it is better to perform several short exposure images than a single long exposure one.</p>

CC BY-SA 3.0
2013-09-30T09:06:08.357Z
2013-12-03T06:53:50.777Z
2013-12-03T06:53:50.777Z
MBR
<p><a href="https://en.wikipedia.org/wiki/Apparent_magnitude" rel="noreferrer">Apparent magnitude</a> is a rather complex way to determine the brightness of a star. Quoting the introduction text from the linked to Wikipedia page:</p>

<blockquote>
  <p>The apparent magnitude (m) of a celestial body is a measure of its
  brightness as seen by an observer on Earth, adjusted to the value it
  would have in the absence of the atmosphere. The brighter the object
  appears, the lower the value of its magnitude. Generally the visible
  spectrum (vmag) is used as a basis for the apparent magnitude, but
  other regions of the spectrum, such as the near-infrared J-band, are
  also used. In the visible spectrum Sirius is the brightest star in the
  night sky, whereas in the near-infrared J-band, Betelgeuse is the
  brightest.</p>
</blockquote>

<p>While it is of course a useful measure also for the slightly more casual, non-scientific observer to help determine the observed star from its neighboring cluster, or identification in general, I always wondered if there is a way to measure apparent magnitude with enthusiast-class equipment, and what would these procedures be?</p>

<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<img src="https://i.sstatic.net/BCsWU.jpg" alt="apparent magnitude"></p>

<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<sup>Apparent magnitude scale and observational limits (Source: <a href="http://sci.esa.int/education/35616-stellar-distances/?fbodylongid=1868" rel="noreferrer">ESA Science</a>)</sup></p>

<p>Also interesting would be a description of what level of precision and enthusiast can get with such equipment while measuring apparent magnitude of a distant star. If you need specifics to answer the question, such as precise available equipment or subject of observations, please feel free to choose at will any that would broadly match the capabilities of enthusiast-grade equipment.</p>

CC BY-SA 3.0
2013-09-28T02:17:57.333Z
You may already have a DSLR, but if you're ready to buy it, a CCD would cost as much. Do you want an answer with CCDs?
Cheeku
CC BY-SA 3.0
2013-09-28T04:21:33.467Z
@Cheeku - Sure, any method that's accessible to enthusiasts will do, thereof my last sentence. If you know of more ways, then the better. There ought not be many ways anyway, so I thought to ask it like that, have answerers demonstrate their ingenuity a little LOL
TildalWave
<luminosity><apparent-magnitude><atmospheric-effects><newtonian-telescope><dobsonian-telescope>
How could a hobbyist astronomer determine apparent magnitude of a star?
TildalWave
# How could a hobbyist astronomer determine apparent magnitude of a star?

(Asked by: username_0 on 2013-09-27)

[Apparent magnitude](https://en.wikipedia.org/wiki/Apparent_magnitude) is a rather complex way to determine the brightness of a star. Quoting the introduction text from the linked to Wikipedia page:

> The apparent magnitude (m) of a celestial body is a measure of its
> brightness as seen by an observer on Earth, adjusted to the value it
> would have in the absence of the atmosphere. The brighter the object
> appears, the lower the value of its magnitude. Generally the visible
> spectrum (vmag) is used as a basis for the apparent magnitude, but
> other regions of the spectrum, such as the near-infrared J-band, are
> also used. In the visible spectrum Sirius is the brightest star in the
> night sky, whereas in the near-infrared J-band, Betelgeuse is the
> brightest.

While it is of course a useful measure also for the slightly more casual, non-scientific observer to help determine the observed star from its neighboring cluster, or identification in general, I always wondered if there is a way to measure apparent magnitude with enthusiast-class equipment, and what would these procedures be?

![apparent magnitude](https://i.sstatic.net/BCsWU.jpg)

Apparent magnitude scale and observational limits (Source: [ESA Science](http://sci.esa.int/education/35616-stellar-distances/?fbodylongid=1868))

Also interesting would be a description of what level of precision and enthusiast can get with such equipment while measuring apparent magnitude of a distant star. If you need specifics to answer the question, such as precise available equipment or subject of observations, please feel free to choose at will any that would broadly match the capabilities of enthusiast-grade equipment.

**Tags:** luminosity, apparent-magnitude, atmospheric-effects, newtonian-telescope, dobsonian-telescope
> **Comments:**
> **username_1**: You may already have a DSLR, but if you're ready to buy it, a CCD would cost as much. Do you want an answer with CCDs?  
> **username_0**: @Cheeku - Sure, any method that's accessible to enthusiasts will do, thereof my last sentence. If you know of more ways, then the better. There ought not be many ways anyway, so I thought to ask it like that, have answerers demonstrate their ingenuity a little LOL  

---

## 2 answers

### Answer by username_3 on 2013-09-30. Score: 20 | Accepted answer

The easiest way to determine the magnitude of a given star is probably to use the Pogson relation. The idea is to determine the magnitude of a star knowing the magnitude of a reference star; it is thus quite easy, using a well-known reference as Vega or Sirius.

The Pogson relation is given by:

$$m\_1-m\_2=-2.5\ log\ \left({\frac{E\_1}{E\_2}}\right)$$

where $m\_1$ and $m\_2$ are the magnitudes of star 1 and star 2 (your reference star), and $E\_1$ and $E\_2$ brightness (that could be in arbitrary units, which is a good news for you).

With a CCD detector the brightness is easy to determine since it's just the flux of a pixel. You don't have to convert it in physical units (as Watt per square meter) since you have a ratio $\left({\frac{E\_1}{E\_2}}\right)$, so the raw intensity is enough to determine the magnitude.

As for any other measurement with a CCD camera, you have of course to determine the bias, dark and flat-field and to reduce your data before estimating any magnitude. The precision will depend on the number of observations performed and, as always, it is better to perform several short exposure images than a single long exposure one.


---

### Answer by username_2 on 2022-09-25. Score: 4

There is a difficulty with measuring magnitude: the atmosphere! It is sometimes clear sometimes hazy and it can be very hard to know just how much light is being lost to a high layer of thin cirrostratus, or a passing puff of mist.

Amateurs have measured star magnitudes by the comparison technique. This is literally comparing the star with other nearby stars of known magnitude and estimating "is it brighter or less bright"

If there are convenient nearby stars of similar magnitude, a good estimate of 0.1 magnitudes is possible by a skilled observer. There are long term sequence of the magnitude of variable stars that have been produced by this method.

It is harder if there is no nearby star of similar magnitude. It is easier to compare two stars in the same field of view, rather than have to move you eyes from one star to another.


---

