Former astronomer here! You can download a lot of data from open access websites such as data.nasa.gov or any of the big digital surveys.

I don’t know about today’s data format, but it used to be all on the FITS format, with lots of libraries in Python/Matlab/etc., and also the excellent SAOImage DS9, all available for free.

Here are some links: sites.google.com/cfa.harvard.edu/…/download en.wikipedia.org/wiki/FITS www.stsci.edu/…/our-collections www.sdss.org/dr19/data_access/