This is a historical event that marks the passing of Pope Gregory XVI, who was the head of the Catholic Church from 1831 to 1846. He was known for his conservative views and his opposition to modernism. His death marked the end of an era and the beginning of a new one
From Wikipedia
Pope Gregory XVI was head of the Catholic Church and leader of the Papal States from 2 February 1831 to his death in June 1846. He had adopted the name Mauro upon entering the religious order of the Camaldolese. He is the most recent pope to take the pontifical name "Gregory", the last to govern the Papal States for the whole duration of his pontificate, and the most recent not to have been a bishop when elected.