The constellation is determined by the Gregorian calendar date. 1The Gregorian calendar date of July 29th, 980 is September 8th, and the constellation of that day is Virgo.
Lunar calendar: July 29th, 80.
Main branch: Geng Shen Yiyou Shen Jia
Gregorian calendar:1Monday, September 8, 980 Virgo
Source: Hua.com.