It is celebrated on the first Sunday after the first full moon after the Vernal Equinox, which usually overlaps with Jewish Passover but not perfectly. Given that the Orthodox Christians are still on the Julian calendar, which is now 13 days behind the Gregorian, their Vernal Equinox is on April 3 in the Gregorian calendar and as a result Easter doesn't fall on the same day for Orthodox and Catholic Christians unless the first full moon after the Vernal Equinox is after April 3 (whatever the barbarous Protestants do is up to them and their heresies).
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*