The sky divided into 27
The moon completes one circuit around Earth in about 27.3 days. Traditional Indian astrology divided that path into 27 equal segments, each called a lunar mansion.
Each lunar mansion spans 13°20′ (thirteen degrees and twenty minutes) and is associated with a ruling planet. They are identified with groups of stars.
How your birth lunar mansion is fixed
The lunar mansion the moon occupies at your moment of birth is the one that counts for you. Traditionally this is one of the most personal details in a chart — used for naming, marriage matching and period calculation.
Working it out needs date, time and place of birth so the moon's position is right. Without a time a lunar mansion can still be produced, but it may differ, so we label such reports as approximate.
Its link to the 120-year planetary period cycle
The entire 120-year planetary period cycle starts from your birth lunar mansion. Every lunar mansion has a ruling planet, and the period of that planet is considered to be running from birth.
That is why the lunar mansion is so central: one position of the moon sets the direction of a 120-year timeline. In our report every time window is derived from that cycle.
Science and tradition
Astronomically, the lunar mansions are a division of the sky — useful and precise for calculation. There is no scientific evidence, however, that a lunar mansion determines temperament or future.
We compute lunar mansions because they are the foundation of the traditional system — not because they are proof of anything ahead.