A national day of mourning will be observed Thursday for former President Jimmy Carter, who died Dec. 29 at 100.Carter, who served as the 39th U.S. president, died at his home in Plains, Georgia. He was the longest-lived U.S. president. President Joe Biden declared Thursday as a National Day of Mourning to honor the former president. In announcing the day of mourning, Biden said: "I call on the American people to assemble on that day in their respective places of worship, there to pay homage to the memory of President James Earl Carter, Jr. I invite the people of the world who share our grief to join us in this solemn observance."Biden also ordered U.S. flags to fly at half-staff for 30 days starting Dec. 29.Carter's state funeral is scheduled for Thursday at the Washington National Cathedral. Biden will deliver a eulogy. Denise Bomberger, a staff member of the Carter Presidential Center, writes “We Love You President Carter” on a chalk board set up in a memorial outside the center on Monday. Jimmy Carter, the 39th president, died Dec. 29 at 100. His funeral will be Thursday in Washington.Joe Raedle/Getty Although not an official federal holiday, Biden's executive order declares all federal agencies — including the U.S. Postal Service — to close their doors Thursday. There will be no mail delivery, and all post offices will be closed.All federal employees should be given the day off except for vital employees important to the country's "national security, defense, or other public need," the announcement said.U.S. stock markets will also be closed Thursday. Both the New York Stock Exchange and Nasdaq announced last week they planned to close their equity and options markets to honor Carter. Banks, schools and other businesses will remain open — although residents should look out for changes in business hours. The national funeral service is scheduled to begin at 9 a.m Central Time. WGN, CNN and CNBC will begin coverage at 8 a.m.PBS News will also begin coverage at 8 a.m. The service can be streamed here.