<p>Magnitude is defined relative to a standard flux of a magnitude 0 object $F_0$.</p>

<p>$$M = -2.5\log(F/F_0)$$</p>

<p>if the error is $F_E$, then $F =F_0\pm F_E$, so the magnitude M is</p>

<p>$$ -2.5\log((F_0+F_E)/F_0) &lt; M &lt;-2.5\log((F_0-F_E)/F_0)$$</p>

<p>The errors here are tiny in comparison to the measured flux, only one part in 10000, so the range of magnitudes is similarly tiny +-0.0001</p>

CC BY-SA 3.0
2018-03-14T15:57:56.610Z
2018-03-14T15:57:56.610Z
James K
<p>I'm working with some data and I have some values named <code>fluxmag0</code> and <code>fluxmag0err</code> that should correspond to the zero point values and error in flux units.</p>

<p>The values are around $10^{13}$ for <code>fluxmag0</code> and $10^9$ for <code>fluxmag0err</code></p>

<p>I need to have the zero point error in magnitude units. If I take $2.5\log_{10}(\mathrm{fluxmag0err})$ the values are huge so I suppose it's not the way to compute this.</p>

<p>How can I convert these values in terms of magnitudes? </p>

<p>Thanks a lot in advance for your help </p>

<apparent-magnitude><magnitude>
How to get the zeropoint magnitude?
sqrt55
# How to get the zeropoint magnitude?

(Asked by: username_0 on 2018-03-14)

I'm working with some data and I have some values named `fluxmag0` and `fluxmag0err` that should correspond to the zero point values and error in flux units.

The values are around $10^{13}$ for `fluxmag0` and $10^9$ for `fluxmag0err`

I need to have the zero point error in magnitude units. If I take $2.5\log\_{10}(\mathrm{fluxmag0err})$ the values are huge so I suppose it's not the way to compute this.

How can I convert these values in terms of magnitudes?

Thanks a lot in advance for your help

**Tags:** apparent-magnitude, magnitude

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## 1 answers

### Answer by username_1 on 2018-03-14. Score: 3

Magnitude is defined relative to a standard flux of a magnitude 0 object $F\_0$.

$$M = -2.5\log(F/F\_0)$$

if the error is $F\_E$, then $F =F\_0\pm F\_E$, so the magnitude M is

$$ -2.5\log((F\_0+F\_E)/F\_0) < M <-2.5\log((F\_0-F\_E)/F\_0)$$

The errors here are tiny in comparison to the measured flux, only one part in 10000, so the range of magnitudes is similarly tiny +-0.0001


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