Fifty days after Easter — the descent of the Holy Spirit on the apostles.
Astronomically anchored to Easter (the first Sunday after the first full moon following the spring equinox in the Western tradition). The date is the same globally each year, though Eastern Orthodox traditions use a different rule.
Pentecost falls 49 days after Easter Sunday and commemorates the descent of the Holy Spirit on Jesus's apostles, as described in the Acts of the Apostles. It is regarded as the birth of the Christian Church and is the third-most important festival in the Christian calendar after Easter and Christmas.
Computed for Zarech'ye (Europe/Moscow) using local sunrise, sunset and astronomical positions.
Daily tithi, nakshatra, sunrise, sunset and upcoming festivals — all computed for Zarech'ye.