What is meant by the ninth day of the month of Ob? on page 17 of the novel

In Isaac Bashevis Singer’s novel The Slave, references to Jewish timekeeping, rituals, and historical memory are deeply intertwined with the story’s themes of exile, faith, and suffering. The "ninth day of the month of Ob" is almost certainly a reference to Tisha B’Av (the Ninth of Av), one of the most solemn fast days in the Jewish calendar which commemorating the destruction of the First and Second Temples in Jerusalem.