The constellation is determined by the date of the solar calendar. The date of June 28th of the Gregorian calendar in 79 is July of 2 1 year, and the constellation of that day is Cancer.
Lunar calendar: 79? June? twenty-eight
Ganzhi: gone? Xin Wei? ugly
Gregorian calendar:1July 2, 9791Saturday Cancer
Source: Hua.com.