[AstroPy] Use of separation

[Emil Lenc]

> On 26 Mar 2021, at 23:05, E. Madison Bray <erik.m.bray at gmail.com> wrote:
> 
> On Fri, Mar 26, 2021 at 10:37 AM Peter Dzwig <pdzwig at summaventures.com> wrote:
>> 
>> 
>> From Emil's mail:
>> 
>> "Also note that the two input coordinates were not in the same frame —
>> one is automatically converted to match the other, ensuring that even
>> though they are in different frames, the separation is determined
>> consistently."
>> 
>> This isn't very clear if the manual doesn't state which way the
>> conversion goes (ie assigns a priority). Preferably the user should be
>> allowed to specify.
> 
> This question also came up a few days ago on the Astropy GitHub:
> https://github.com/astropy/astropy/issues/11388
> 
> The response is the same, though on the issue I proposed modifying the
> documentation to make this point more prominent in the documentation
> on separations and offsets.
> 
> I also proposed maybe adding an optional frame= argument to
> separation() in order to explicitly provide the frame, but I'm not
> sure if that's really useful.
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I think if the documentation on this point were clearer then that would help tremendously.

Cheers,

Emil.