I've been doing a bit of research on the limits of human vision today, as I was wondering if any ancient humans (say, at Newgrange) would ever have been able to

I've been doing a bit of research on the limits of human vision today, as I was wondering if any ancient humans (say, at Newgrange) would ever have been able to discern the spiral of a galaxy with their naked eye... According to what you're saying, I think it's just about possible. M51's spiral features are 20 arcseconds, and you can apparently resolve 15... And turns out M51, the easiest spiral galaxy to view, would have been directly overhead Stonehenge (the best viewing position). So... Might be somethin' for you to try, if you ever get somewhere extremely dark and perfectly clear? M51: https://duckduckgo.com/?q=%22m51%22&t=ffab&atb=v340-1&iax=images&ia=images https://duckduckgo.com/?q=%22m51%22&t=ffab&atb=v340-1&iax=im... Newgrange: https://duckduckgo.com/?t=ffab&q=newgrange+spirals&atb=v340-1&iax=images&ia=images https://duckduckgo.com/?t=ffab&q=newgrange+spirals&atb=v340-...