Because most Orthodox Christians celebrate Christmas two weeks after Western churches, holiday festivities are still happening around the world. Orthodox Christians, Greek Catholics and Coptic Christians will observe Christmas this Saturday everywhere from Russia to Israel to Canada.

"This joyful time of year is an opportunity to gather with family and friends to reflect on the many blessings in our lives. It also gives us a chance to reaffirm our commitment to live in a peaceful, inclusive society," Canadian Prime Minister Justin Trudeau said in a Friday news release. "Let us also use this occasion to show greater compassion and humanity to those most vulnerable, at home and around the world."

Here's what you need to know about the holiday.

Why is it celebrated Saturday?

Pope Gregory XIII made the Gregorian calendar, or “Western calendar,” in 1582, but not everyone switched over from the Julian calendar created under the rule of Roman leader Julius Caesar. In the Gregorian calendar, Christmas is Dec. 25 — which translates to Jan. 7 on the Julian calendar.

orthodox christmas5 Believers attend a service on the eve of Orthodox Christmas at the Volodymyrsky Cathedral in Kiev, Jan. 6, 2016. Photo: REUTERS/Valentyn Ogirenko

Who celebrates Christmas in January?

Fifteen Eastern Orthodox churches, including ones in Ukraine, Georgia and Serbia, recognize Christmas annually on or near Jan. 7. Ethiopian and Egyptian Coptic churches observe the holiday during the first month of the year, as well, as do more than 80 percent of Orthodox Christians living in Russia, according to ReadtheSpirit.com.

orthodox christmas6 Russian President Vladimir Putin attends the Orthodox Christmas service in the settlement of Turginovo in Tver region, Russia, Jan. 7, 2016. Photo: REUTERS/Aleksey Druzhinin/Sputnik/Kremlin

How is it different from Christmas in the West?

Orthodox Christians celebrate Christmas differently from Western customs,  according to the Christian Post. While traditions like putting up the Christmas tree and giving gifts happen during both holidays, the Orthodox Church stresses the spiritual side of the season.

orthodox christmas 3 Pope Tawadros II, the 118th Pope of the Coptic Orthodox Church of Alexandria and Patriarch of the See of St. Mark Cathedral, leads Egypt's Coptic Christmas eve mass in Cairo, Jan. 6, 2016. Photo: REUTERS/Amr Abdallah Dalsh

Fasting and charity are prominent features of the Christmas season for Eastern Christians, along with numerous services of worship.

orthodox christmas7 Women dressed in traditional costumes sing Christmas carols as they gather to celebrate the Orthodox Christmas at a compound of the National Architecture museum in Kiev, Jan. 7, 2016. Photo: REUTERS/Valentyn Ogirenko

What is the Eastern Christmas feast like?

While meat is a staple during holiday lunches and dinners in the West, many Orthodox Christians refrain from eating such products during the holidays. Celebrations also involve the setting of places at the table for the spirits of relatives who have died and a 12-course Christmas Eve dinner with beets, potatoes and pierogies, according to CBC.

Orthodox Christmas4 Believers attend a service on the eve of Orthodox Christmas at the Volodymyrsky Cathedral in Kiev, Jan. 6, 2016. Photo: REUTERS/Valentyn Ogirenko