What are the days when the sun dies?

You're talking about the anniversary of Yang Gong's death. "The Death of Yang Gong", also known as "Thirteen Taboos in Yang Gong", was handed down by Yang Junsong, a geomantic master in the Tang Dynasty. These thirteen "taboo days" are 1 month 13, February 1 day, March 9, April 7, May 5, June 3, July1day, July 29, and July 29.