Add a feature to calculate linear distances between objects in images
Stacking program, astrometric (plate) solver, fits file viewer
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han59
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Hey everyone,
I've been using ASTAP for a while now for astrometry and photometry, and it's super handy for processing my astro images. But one thing I've noticed is that while it does a great job calculating angular separations based on pixel distance and the field of view (FOV), there's no built-in way to convert that to actual linear distances—like in light-years, parsecs, kilometers, or whatever units make sense. It'd be awesome if we could add something like that!
Basically, the idea is: After solving the astrometry, let users pick two objects or points in the image, calculate the angular separation from pixels and FOV, and then turn that into a physical distance. You'd need the distance to the objects, which could come from integrated catalogs like Gaia (for parallax/distances) or just let the user input it manually if it's not available.
Why add this? Well, it would make ASTAP even more powerful for analysis without having to jump to other tools. Right now, I end up exporting data and crunching numbers in excel or something, which is a hassle. This feature would save time and keep everything in one place.
Plus, it'd be great for both pros and hobbyists—think about measuring sizes of star clusters or galaxies directly in the software. It could make ASTAP stand out more compared to stuff like AstroImageJ or DS9 that have similar measuring tools.
How could it work? Something simple: Select two points, get the angular sep in arcseconds or degrees, multiply by the distance (in parsecs or whatever) to get linear distance, and display it in user-chosen units (ly, pc, km, AU, etc.). Maybe integrate it with the annotation tools or viewer menu.
For examples:
In a pic of the Pleiades cluster, measure the light-years between stars to study its structure.
For binary stars like Alpha Centauri, get the AU separation to think about orbits.
On galaxy images like Andromeda, calculate its diameter in parsecs—super useful for comparing to known data.
Even for solar system stuff, like asteroid distances in km.
What do you think, Han or anyone else? Is this doable? I'd love to hear feedback or if there's a workaround I'm missing.
Thanks!
Jordi
The distance of far away stars is know very accurately since Gaia measurements. From that 3d models have been made. If I remember well, even before Gaia measurements there was a simulation where you could travel like spaceship through the galaxy. But that would require an application where you can create and rotate a 3d view of the star database. Probably nice to play with but I'm afraid that is more a space simulator then a FITS file viewer. Doable but a lot of work. It is probably better first to look for a simulator already existing and available.
Cheers, Han
Hello Han,
The request is much simpler than this. I'm attaching some examples.
Cheers
Okay you could extract the parallax from Simbad
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=M27
The M27 parallax is 2.57 milli arcseconds. Then the distance is 1000/2.57=389 parsec. But that would require for each object to extract the parallax. What if two object are visible? The current setup is that you can go from an image position or field to Simbad or Gaia to get more information of that sky area with the popup menu "online query".
The parallax(mas)/distance(ly)s is an indirect measurement you would have to extract it from Simbad or an other source. The only thing you could measure from the image in the angular diameter, position and magnitude.