Millions of Christians worldwide have celebrated Orthodox Christmas on Jan. 7, nearly two weeks after much of the globe observed the holy day celebrating the birth of Jesus.

Orthodox Christians in countries stretching from Ethiopia to Russia celebrate Christmas on Jan. 7--rather than Dec. 25, according to The Associated Press.

That is due to certain Eastern Orthodox churches, including those in Russian traditions, following the ancient Julian calendar, according to the Ethiopian News Agency.

This calendar is 13 days behind the Gregorian calendar, which is used by Catholic and Protestant churches and by much of the secular world for everyday purposes, The Independent reported on Jan, 7.

The Ethiopian Orthodox Church and some other Oriental Orthodox churches – distinct from Eastern Orthodox but sharing many traditions – also marked Christmas on that day.

Still, other Eastern Orthodox communities, such as those in the Greek tradition, celebrate Christmas on Dec.25, aligning with Catholic and Protestant churches.

Sixteenth century Pope Gregory XIII approved a revised, more astronomically precise calendar, which bears his name.

It shifted the calendar several days forward to make up for lost time (literally) and added a more precise calculation of leap years.

Protestant churches eventually followed the Catholic lead in adopting the calendar, as did secular governments.

All Eastern Orthodox kept to the old calendar until 1923, when an inter-Orthodox gathering adopted a revised Julian calendar that essentially mirrors the Gregorian.

Most (but not all) churches in the Greek Orthodox tradition have adopted this, as have those in Romanian, Bulgarian and other traditions.

         PUTIN CELEBRATES CHRISTMAS AT ORTHODOX SERVICE

In Moscow, Russian President Vladimir Putin celebrated Christmas Eve at an Orthodox service on the evening of Jan. 6.

He was joined by veterans of Russia's continuing war in Ukraine and their families, and he addressed the children in attendance, Africa News reported.:

"Russia's warriors have always, as if at the Lord's behest, carried out this mission of defending the Fatherland and its people, saving the Motherland and its people. At all times in Russia, this is how people have regarded their warriors, as those who, as if at the Lord's behest, carry out this holy mission," Putin was quoted as saying.

The Russian Orthodox Church is the world's largest Orthodox denomination.

Like other Eastern Orthodox churches, it follows the Julian calendar, which runs 13 days later than the Gregorian calendar, used by Catholic and Protestant churches. Christmas is celebrated on Jan. 7 and a service is held on the night of Jan. 6.

But the Russian Orthodox Church, the largest communion in Eastern Orthodoxy, has stayed on the old calendar, observing Christmas on Jan. 7 on the new calendar, as have Serbian, Georgian and some other Orthodox.

Some Orthodox in Ukraine have begun to observe Christmas on Dec. 25, while others have retained the Jan. 7 observance.

One exception is the Armenian Orthodox tradition, which observes Christmas on Jan. 6.

In the United States, observances vary. Churches in the Greek and Antiochian traditions observed Christmas on Dec. 25. Some churches in the Slavic tradition, including Serbian and smaller Russian churches, observe it on Jan. 7.

In Africa, Egypt's Coptic Orthodox Christians attended Mass to celebrate Christmas Eve on Jan. 6.

Egyptian president Abdel Fattah El-Sissi attended several previous Christmas Eve services held by the country's Coptic Orthodox minority.

This year, the Egyptian government declared Jan. 7 a paid public holiday to observe Christmas.

The Copts in Egypt, a predominantly Muslim country, are among the world's oldest Christian communities.

Orthodox Christians are the overwhelming majority of Egypt's Christians, who account for about 10 percent of the country's 108 million population.