<p>In the JPL small body browser, orbital elements are all provided with uncertainties and even a covariance matrix, such as for <a href="https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013LA2;cad=1;old=0;orb=0;cov=1;log=0#elem" rel="noreferrer">2013 LA2</a>.  Very good.  But underneath, the absolute magnitude is reported with a sigma of "n/a".  Why would the uncertainty for an absolute magnitude be not applicable?  Is it not a measurement but somehow given by definition?</p>

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2018-07-10T14:43:22.583Z
@barrycarter Even if true, even when there are only one or two measurements, there is still a measurement uncertainty; it just can't be estimated as the standard deviation from repeated measurements.
gerrit
<observational-astronomy><absolute-magnitude>
In the JPL small body browser, why is uncertainty on absolute magnitude "N/A"?
gerrit
# In the JPL small body browser, why is uncertainty on absolute magnitude "N/A"?

(Asked by: username_0 on 2018-07-10)

In the JPL small body browser, orbital elements are all provided with uncertainties and even a covariance matrix, such as for [2013 LA2](https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013LA2;cad=1;old=0;orb=0;cov=1;log=0#elem). Very good. But underneath, the absolute magnitude is reported with a sigma of "n/a". Why would the uncertainty for an absolute magnitude be not applicable? Is it not a measurement but somehow given by definition?

**Tags:** observational-astronomy, absolute-magnitude
> **Comments:**
> **username_0**: @barrycarter Even if true, even when there are only one or two measurements, there is still a measurement uncertainty; it just can't be estimated as the standard deviation from repeated measurements.  

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## 0 answers

