<p>I'm playing around with the data in the <a href="https://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=V/154&amp;-out.max=50&amp;-out.form=HTML%20Table&amp;-out.add=_r&amp;-out.add=_RAJ,_DEJ&amp;-sort=_r&amp;-oc.form=sexa" rel="nofollow noreferrer">SDSS DR16</a>, but the magnitudes have huge uncertainties:</p>
<pre><code>for i in ['umag', 'gmag', 'rmag', 'imag', 'zmag']:
    print(max(dataset[i]))

30.889
26.3114
26.5881
29.9517
24.465


for i in ['e_umag', 'e_gmag', 'e_rmag', 'e_imag', 'e_zmag']:
    print(max(dataset[i]))
    
2661440.0
37.8006
25.9054
2392490.0
113.926
</code></pre>
<p>Why are the errors so large? Could they be millimags? But even then, <code>e_umag</code> and <code>e_imag</code> are enormous, compared to the measurements. A comment on <a href="https://astronomy.stackexchange.com/questions/33834/acceptable-errors-in-photometric-measurements">this question</a> states that errors should be ~0.01.</p>

CC BY-SA 4.0
2022-04-06T20:54:50.303Z
Why are you printing the maximum value (which will most probably be a large number).
ProfRob
CC BY-SA 4.0
2022-04-06T21:04:44.063Z
Error is quoted as being in the range [1.5e-5...100] in the Vizier table with '100' being set in the event of issues in the fit so `max()` is definitely not going to give a representative value for the typical magnitude error
astrosnapper
CC BY-SA 4.0
2022-04-06T21:50:48.887Z
My question is *why* are they so large, especially if the range is supposed to be [1.5e-5...100] ?
Jim421616
CC BY-SA 4.0
2022-04-07T17:02:36.147Z
100 is being used in this instance as a replacement for null/missing/bad values; not all table formats support the concept of null values.
astrosnapper
<photometry><magnitude>
Errors in photometric magnitudes from SDSS DR16
Jim421616
# Errors in photometric magnitudes from SDSS DR16

(Asked by: username_0 on 2022-04-06)

I'm playing around with the data in the [SDSS DR16](https://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=V/154&-out.max=50&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa), but the magnitudes have huge uncertainties:

```
for i in ['umag', 'gmag', 'rmag', 'imag', 'zmag']:
    print(max(dataset[i]))

30.889
26.3114
26.5881
29.9517
24.465

for i in ['e_umag', 'e_gmag', 'e_rmag', 'e_imag', 'e_zmag']:
    print(max(dataset[i]))
    
2661440.0
37.8006
25.9054
2392490.0
113.926

```

Why are the errors so large? Could they be millimags? But even then, `e_umag` and `e_imag` are enormous, compared to the measurements. A comment on [this question](https://astronomy.stackexchange.com/questions/33834/acceptable-errors-in-photometric-measurements) states that errors should be ~0.01.

**Tags:** photometry, magnitude

> **Comments:**
> **username_1**: Why are you printing the maximum value (which will most probably be a large number).  
> **username_2**: Error is quoted as being in the range [1.5e-5...100] in the Vizier table with '100' being set in the event of issues in the fit so `max()` is definitely not going to give a representative value for the typical magnitude error  
> **username_0**: My question is *why* are they so large, especially if the range is supposed to be [1.5e-5...100] ?  
> **username_2**: 100 is being used in this instance as a replacement for null/missing/bad values; not all table formats support the concept of null values.  

---

## 0 answers

