<p>I have noticed in my experience that the coordinate solution within the headers of default reduced images from radio interferometers are commonly trustworthy to the arcsecond or less. From IR and optical observatories it is never so simple: the header solution from the default images is at most useful as a very rough guidance, off by an arcminute or more. Sometimes there is no useful header whatsoever, and the user needs to compare with, e.g., DSS of 2MASS to get good coordinates for her images, if she cares about that at all.</p>

<p>This has other consequences which in my opinion affect the idiosyncrasy of optical and radio astronomers, for example:</p>

<ul>
<li>No coordinates in published figures is much more common within the optical-IR community than in the radio community</li>
<li>Finding charts. Radio astronomers do not know what are they, because they are not needed for radio observations.</li>
</ul>

<p>Radio telescopes (this depends on the frequency also) sometimes require doing pointing calibrations during the observations. But in optical telescopes they also often require a guiding star, whose coordinates I imagine are properly tabulated. Regardless, the delivered images do not end up with a proper header.</p>

CC BY-SA 4.0
2018-11-17T07:55:40.673Z
Please provide links to some examples and describe which telescopes they have come from.
ProfRob
CC BY-SA 4.0
2018-11-17T10:38:04.743Z
I'm going to echo Rob Jeffries' request: can you provide some examples? (I note that you seem to think 2MASS provides good coordinates -- which it does -- and those are IR images...)
Peter Erwin
CC BY-SA 4.0
2018-11-17T15:51:07.823Z
My guess is that interferometers require a very accurate knowledge of where each telescope is pointing, so knowing and getting it correct are vital.  Single-aperture telescopes, unless they are trying to do precision astrometry, only need the star to land reasonably close to the center of their field of view because they are looking at the star itself, not necessarily trying to measure its position. Optical telescopes using guide stars to do atmospheric corrections generate their own "stars" with a laser, so position of the guide star is irrelevant.
Dave
<observational-astronomy><coordinate>
Why do default coordinates from IR-optical observatories are usually not trustworthy, while from radio interferometers they usually are?
guest
# Why do default coordinates from IR-optical observatories are usually not trustworthy, while from radio interferometers they usually are?

(Asked by: username_0 on 2018-11-17)

I have noticed in my experience that the coordinate solution within the headers of default reduced images from radio interferometers are commonly trustworthy to the arcsecond or less. From IR and optical observatories it is never so simple: the header solution from the default images is at most useful as a very rough guidance, off by an arcminute or more. Sometimes there is no useful header whatsoever, and the user needs to compare with, e.g., DSS of 2MASS to get good coordinates for her images, if she cares about that at all.

This has other consequences which in my opinion affect the idiosyncrasy of optical and radio astronomers, for example:

* No coordinates in published figures is much more common within the optical-IR community than in the radio community
* Finding charts. Radio astronomers do not know what are they, because they are not needed for radio observations.

Radio telescopes (this depends on the frequency also) sometimes require doing pointing calibrations during the observations. But in optical telescopes they also often require a guiding star, whose coordinates I imagine are properly tabulated. Regardless, the delivered images do not end up with a proper header.

**Tags:** observational-astronomy, coordinate

> **Comments:**
> **username_1**: Please provide links to some examples and describe which telescopes they have come from.  
> **username_2**: I'm going to echo Rob Jeffries' request: can you provide some examples? (I note that you seem to think 2MASS provides good coordinates -- which it does -- and those are IR images...)  
> **username_3**: My guess is that interferometers require a very accurate knowledge of where each telescope is pointing, so knowing and getting it correct are vital.  Single-aperture telescopes, unless they are trying to do precision astrometry, only need the star to land reasonably close to the center of their field of view because they are looking at the star itself, not necessarily trying to measure its position. Optical telescopes using guide stars to do atmospheric corrections generate their own "stars" with a laser, so position of the guide star is irrelevant.  

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## 0 answers

