This article from Chabad.org explains the origins, historical background, and ritual observances of the minor fast day of Tzom Gedaliah, observed on the day after Rosh Hashanah. This fast commemorates the assassination of Gedaliah, the Babylonian-appointed governor of Judea, who was murdered by fellow Jews. Rabbi Menachem Posner is an educator, staff writer at Chabad.org and contributor to several online Jewish newspapers.