Is it permissible to pray in the mosque if the prayer time is advanced before its lawful time based on astronomical calculations, or must one pray at home, or must one repeat it at home?

Astronomical calculations are not to be relied upon for prayer times; rather, the legitimate cosmic signs are. So, whoever is certain that a congregation performs the prayer before its prescribed time, his prayer with them is not valid, and he must pray individually at home if he does not find another congregation that prays at the correct time.