I belong to the Year of the Sheep. What constellation is the thirteenth day of the first month?

The constellation is determined by the date of the solar calendar. You should use the solar calendar date to query the constellation. If you use the lunar calendar date, you need to specify the year to convert the lunar calendar date into the solar calendar date for query. You can't say "sheep" because each sheep has a different solar calendar date on the thirteenth day of the first month. You fill in the year. I can help you.