The idea is that the earth is constantly rotating, and the two signs that co-exist at the time you enter this world both impact who you are as a person throughout your life. According to Keen.com, an online source of psychic advice and information, people in ancient times “noticed that the sign rising in the east at the time of a person’s birth gave them definable characteristics that complemented their Sun sign. This became known as the person’s ascendant sign. It is separate and distinct from the person’s sun sign.”
