In some Eastern European and Middle Eastern countries, Christmas is officially celebrated on January 7.
That is because numerous Orthodox Christian churches follow the Julian calendar for religious celebrations.
The Julian calendar runs 13 days behind the Gregorian calendar, the standard international calendar in use today.
The Julian calendar took effect under the reign of Julius Caesar in 45BC.
In 1582, Pope Gregory XIII created a new calendar to correct the discrepancy between calendar time and calculated astronomical time. It became known as the Gregorian calendar.
But to begin with, only Catholic countries adopted the changes and Orthodox Christian countries remained on the Julian calendar.
Over time, those countries adopted the Gregorian calendar for secular use but the Orthodox churches continued to base their liturgical calendar on the Julian timetable.
In 1923 a revised version of the Julian calendar was introduced bringing Christmas Day in line with the Gregorian calendar, but it was only adopted by some of the Orthodox Christian countries including Greece, Cyprus and Romania.
Russia, Ukraine, Serbia, Belarus, Egypt, Ethiopia, Georgia, Kazakhstan, North Macedonia, Moldova and Montenegro continue to celebrate Christmas on January 7.
Many Orthodox and western Christmas traditions are the same, like Christmas trees, gift-giving and carols.
For most Orthodox Christians, Christmas is the beginning of celebrations after 40 days of fasting.
People who observe [the nativity fast] don't eat meat or dairy foods for that period.
While each Orthodox Christian country has its own unique traditions, they all include church services and great feasts.
Many have their own version of Santa Claus too, like in Russia where Ded Moroz (Grandfather Frost) and his granddaughter Snegurochka (Snow Maiden) deliver presents to the children.