How wrong can a Moon sign be?

When a birth time is missing, almost every astrology tool calculates from midday. It is a reasonable choice — midday is the middle of the possible range, so it minimises the average error. The question nobody answers is how often that still lands in the wrong sign.

Gori was run over 400 consecutive days at every hour of the day — 9,600 charts — comparing the Moon sign from the real hour against the Moon sign from midday.

The midday answer was in the wrong sign 1,040 times out of 9,600: 10.8%. Roughly one chart in nine.

The arithmetic agrees independently. The Moon covers about 13° a day, so the average gap between the midday Moon and the real one is around 3.3°, and a sign is 30° wide. 3.3 ÷ 30 is about 11%. When a measurement and a back-of-envelope calculation land in the same place, both are probably right.

It means a Moon sign without a birth time is usually right and occasionally not — and there is no way to tell from the outside which kind you have. If your birth date falls on a day the Moon changed sign, your odds are much worse than one in nine; if it does not, they are much better.

So Gori will tell you the Moon sign, and will not build an argument on it alone when the time is missing. It also drops the Moon out of the element and modality counts in that case: a balance of nine placements you can trust is better than ten where one might be lying.

Barely. The Moon is calculated geocentrically, so your position on Earth shifts it by less than a degree — enough to matter at the very edge of a sign and nowhere else. The time is what matters. The place is what matters for the Ascendant and the houses.