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I have a HYG catalogue and I'd like to filter out stars visible at night and in Europe.

Doesn't have to be exact. I was assuming that it'll be all stars with positive declination, but I wasn't sure about RA values.

Thanks, Michal

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In the answer you can find an example how to convert celestial coordinates to horizon coordinates an than check, if the altitude is above the horizon

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Thank you for pointing me in the right direction. I'm probably going to use PyEphem for this – Michal Holub Jul 1 '14 at 7:48
I did and it worked great. One comment for future followers - if you're crosschecking alt/az with Stellarium (for example), don't forget that pyephem works in UTC timezone by default while Stellarium uses yours....too me a few hours to realize this – Michal Holub Jul 10 '14 at 10:17

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