Some Slavic pagan reconstructionist groups have a special day for the Dark God on Leap Year Day. This day may be for Koschei, Chernobog, or the Dark Face of Veles.
Leap years are years that have an extra day, and they happen every 4 years, in our current calendar system. The extra day is February 29th, and some cultures have holidays for Leap Year's Day. One of those is the reconstructed pagan religion, Ukrainian Ridnoveri, and other Slavic pagan groups. But they use the Slavic calendar, which is the same as the Orthodox calendar in use in Slavic countries, based on the old Julian calendar, rather than the Gregorian calendar in use in Western countries. Slavic February 29th is not the on same day as our February 29th in the English speaking world.
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