A day of mourning was a day designated by government officials for people to mourn the loss of individuals in tragic circumstances. In 2372, the President of the United Federation of Planets, Jaresh-Inyo, called for a day of mourning on Earth after the bombing of the Antwerp Conference by a Changeling in the city of Antwerp, which killed 27 people, including Humans, Tholians, Paradans and Romulans. (DS9: "Homefront")