Lay your two moons over each other

How the score is worked out

There is nothing mysterious in the arithmetic. Each birthday gives one moon with a lit fraction and a lit side, right for a growing moon and left for a shrinking one. When the two moons are lit on opposite sides their light adds together, so a waxing crescent and a waning gibbous can fill almost the whole disc between them. When they are lit on the same side the light overlaps instead, and the score is simply the larger of the two.

That is why two full moons do not score higher than one, and why two people born under opposite phases score well. The trend is about complement rather than sameness, which is a rather nicer idea than most compatibility gimmicks manage.

What it does not mean

A number here is not a verdict on a relationship, a prediction, or advice. Nobody has ever shown that the shape of the Moon on two birthdays has anything to do with how two people get along. Read it the way you would read any old piece of folklore: as a prompt for a conversation, and as something to enjoy. Everything on Arcana Sky is for entertainment and reflection.

If you would rather look at one moon properly, the birthday moon phase calculator gives the exact shape, the lit percentage, the sign the Moon was travelling through and a longer reflection from Selene.