In astrology, the position of the sun at the time of your birth determines your sun sign or, as it's more commonly known, your star sign. The sun is deemed very important in astrology; it rules willpower and ego and is fundamental to who a person is and what they're about. The position of the other planets at the time you were born also has an effect on how you behave, but it's the sun's position, over all the other planets' positions, that is taken into account when determining a person's ...