Just DON'T think of an EOS20 (now obsolete, surprise, surprise). As a Canon user for 40+ years I would very strongly recommend Nikon. Our son has a Nikon (not sure which, but not too expesnive) for astro photography and it's very good.
Having had a good number of different cameras in our family, the very best bar none was a Fuji 9600 zoom - fairly cheapo digi which unfortunately does not have interchangeable lenses but the pictures from which beat anything else we've had (including my Canon with "L" lenses)