Zheng Xuan 鄭玄, who had a profound study of ritual, had from time to time discussed his views over some etiquettes of ritual during his interpretation of the Shijing 詩經. He had once discussed about the etiquette of marriage in the poem "Choumou 綢繆," and his understanding was very different from the classical interpretation provided by Mao's Commentary (毛傳). Undoubtedly he received many criticisms from other Shijing scholars. Mao mentioned that marriage ceremony should take place between October and January in the following year. Zheng did not agree and insisted that such ceremony should only take place in February of each year. The key difference was their interpretation of what the "three stars" were. For Mao, the "three stars" were named "Shen參" in the west of the sky. But Zheng thought that it meant another one in the east named "Xin心." The astrological difference in the two stars, which came out in different months, obviously resulted in the difference in the two scholars' interpretation of the good timing to get married. When Zheng developed his view, he had considered that people got married for the purpose of bearing children and inheriting one's family tradition. He discovered that in the guaqi shuo 卦氣說 written by Meng Xi孟喜, February was the fertility period as "yin meets yang" (yin yang jiao hui 陰陽交會) during this month. So he thought that it was reasonable to interpret the "three stars" as "Xin." The following discussion emphasizes the reasons why Mao and Zheng had such a difference in understanding the "three stars." It is concluded that Zheng's use of ritual to interpret the Shijing is a good proof of the influence of the Yijing 易經 in the Han dynasty.