In the 13 Moon calendar, why doesn each moon (month) begin on the full or new moon?
This is because the 13 moon calendar uses the mean or average measure of the moon, 28 days. The 28-day cycle is the cycle of the moon making one orbit around the Earth – when seen from space. This is the median between the 29.5-day synodic cycle of the moon (new moon to new moon) and the 27.1-day sidereal cycle of the moon (returning to the same position in the sky) – both the synodic and sidereal cycles are lunar measures as seen from Earth. Hence, the perfect measure of Earth’s solar orbit uses the 28-day lunar standard (13 x 28 = 364). The moon orbits the Earth 13 times in one year. It is also interesting to note that each day the moon moves 13 degrees of an arc across the sky.
