<p>By moving the cursor over &quot;<strong>ICRS</strong> coord. <em>(ep=J2000)</em>&quot;
you can display a tooltip, which says:</p>
<blockquote>
<p>Syntax of coordinates is : &quot;ra dec (wtype) [error ellipse] quality bibcode&quot; :</p>
<ul>
<li><em>[error ellipse]</em> :  measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),<br/>
position angle (in degrees North celestial pole to East)</li>
</ul>
</blockquote>
<p>So I read <strong><code>[ 3.69 1.67 90 ]</code></strong> as an uncertainty of:</p>
<ul>
<li>3.69 milliarcseconds (0.246 milliseconds of time) east-west</li>
<li>1.67 milliarcseconds north-south</li>
</ul>

CC BY-SA 4.0
2022-09-20T18:29:54.463Z
Thus, is it 1.0250000000000001e-06 get that would be displayed in Gaia Archive?
Elena Greg
CC BY-SA 4.0
2022-09-20T20:40:19.297Z
@ElenaGreg The [SIMBAD position](http://simbad.u-strasbg.fr/simbad/sim-id?Ident=eps%20Ori)'s bibcode link indicates that it's from Hipparcos. Different observing programs have different error ellipses. I think ε Ori is too bright for Gaia anyway.
Mike G
CC BY-SA 4.0
2022-09-20T14:00:21.407Z
2022-09-20T14:00:21.407Z
Mike G
<p>How to determine errors in ICRS coordinates from the SIMBAD error ellipse, please?
Thank you</p>
<p><a href="https://i.sstatic.net/wuGYa.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/wuGYa.png" alt="enter image description here" /></a></p>

<coordinate><simbad>
How to determine errors in coordinates from SIMBAD error ellipse
Elena Greg
# How to determine errors in coordinates from SIMBAD error ellipse

(Asked by: username_0 on 2022-09-17)

How to determine errors in ICRS coordinates from the SIMBAD error ellipse, please?
Thank you

[![enter image description here](https://i.sstatic.net/wuGYa.png)](https://i.sstatic.net/wuGYa.png)

**Tags:** coordinate, simbad

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## 1 answers

### Answer by username_1 on 2022-09-20. Score: 2

By moving the cursor over "**ICRS** coord. *(ep=J2000)*"
you can display a tooltip, which says:

> Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
>
> * *[error ellipse]* : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),  
>   position angle (in degrees North celestial pole to East)

So I read **`[ 3.69 1.67 90 ]`** as an uncertainty of:

* 3.69 milliarcseconds (0.246 milliseconds of time) east-west
* 1.67 milliarcseconds north-south

> **Comments:**
> **username_0**: Thus, is it 1.0250000000000001e-06 get that would be displayed in Gaia Archive?  
> **username_1**: @ElenaGreg The [SIMBAD position](http://simbad.u-strasbg.fr/simbad/sim-id?Ident=eps%20Ori)'s bibcode link indicates that it's from Hipparcos. Different observing programs have different error ellipses. I think ε Ori is too bright for Gaia anyway.  

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