Introduction to the Big Three
The Sun sign, Moon sign, and Rising sign, also known as the Ascendant, are considered the most important components of a birth chart in astrological tradition. The Sun sign is believed to represent a person's inner nature and character, the Moon sign is associated with their emotional and instinctual side, and the Rising sign is thought to signify how they present themselves to the world.
Computing the Big Three
The Sun sign is the easiest to calculate, as it is simply the zodiac sign that the Sun was in at the time of an individual's birth. The Moon sign is also determined by the Moon's position at birth, but its calculation is more complex due to the Moon's faster orbital period. The Rising sign, or Ascendant, is the zodiac sign that was rising on the horizon at the exact time and location of an individual's birth, making its calculation the most complicated of the three.
Speed and Movement
The Sun takes approximately 365.25 days to complete one orbit around the Earth, which is why we have a birthday every year. The Moon, on the other hand, takes only about 27.3 days to complete one orbit, resulting in a new Moon sign every 2-3 days. The Ascendant, being dependent on the time and location of birth, changes every 2 hours, which is why the time of birth is crucial in determining the Rising sign.