[AstroPy] Query for Messier objects in a given region

[Doug Burke]

Jim,

I second Eric's suggestion that you store the database contents for
searches/queries that are not likely to change if possible. I know of one
person who recently had to take down a really useful Astronomy-based web
service because they were being flooded with requests for data just like
the Messier catalog - i.e. something that doesn't change often - which
ended up causing the hosting service to stop supporting it. There's also
the environmental cost of repeatedly requesting information that doesn't
change (something I know my code should be more aware of).

Doug

On Mon, Apr 12, 2021 at 8:24 AM Eric Jensen <ejensen1 at swarthmore.edu> wrote:

> Hi Jim,
>
> > On Apr 11, 2021, at 8:25 PM, Jim Singh <jimmyboysingh at gmail.com> wrote:
> >
> > What you suggest is certainly an option, but in the first instance I
> wanted to see if I could get away without having to download and store any
> reference data locally. Also, do not RA/Dec values drift over time, so
> real-time DB access assures the latest for one's plots?
>
> The direction of Earth’s pole is constantly changing due to precession,
> but the coordinates of objects in catalogs are tabulated at a fixed
> reference date (called the *equinox* of the coordinates, currently usually
> the year 2000).  So you won’t get “fresher” coordinates by downloading them
> each time - they will always be the same.  (And it will always be slower to
> download the list than to read it from a local file.). Also, precession
> doesn’t change the positions of objects *relative to each other* - it just
> slowly moves the grid.
>
> For high-proper-motion objects (like asteroids or other solar system
> objects) you do need to update coordinates for the current date (to correct
> for the objects’ intrinsic space motion rather than the slow drift of the
> pole), but that’s not an issue for Messier objects or bright stars - those
> objects’ proper motions are negligible for your purposes.
>
> Eric
>
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