What the Moon governs
The Moon covers immediate reaction, appetite, sleep, memory and the conditions someone requires to feel secure. It is read for the body as well as the mood, since it traditionally governs fluids, digestion and the rhythms of daily life. Where the Sun states a direction, the Moon states a requirement, and a requirement can be met by circumstances the person did not consciously choose.
In practice the Moon is often what people around someone experience first, particularly in a household. It shows under pressure, when there is no time to compose a response.
Two and a half days in a sign
The Moon crosses the whole zodiac in about twenty-seven and a third days, which works out at roughly two and a half days in each sign. That speed makes it the most personal of the placements. Two people born on the same date in different hours can hold different lunar signs, and the Moon moves about twelve to fifteen degrees a day, so even the degree shifts noticeably between morning and evening.
The consequence is practical. If a birth time is unknown, the lunar sign is uncertain on a meaningful share of dates, and any reading built on it should be treated as provisional until the time is confirmed.
Rulership and dignity
The Moon rules Cancer and is exalted in Taurus. It is in detriment in Capricorn and in fall in Scorpio. Like the Sun it governs one sign only, and the two luminaries divide the zodiac between them in the classical scheme, with Cancer and Leo sitting side by side at the centre of it.
The fall in Scorpio and detriment in Capricorn are both about restraint. Neither sign allows a need to be stated plainly, which is the specific difficulty rather than a general weakness.
Phase, and no retrograde
The Moon never turns retrograde, for the same geometric reason the Sun does not. What it has instead is phase. The angular distance between the Moon and the Sun at birth gives the natal lunar phase, and some traditions read a waxing chart as forward-looking and a waning one as consolidating. This is a genuine distinction in the chart data, but it is a secondary layer and not every practitioner uses it.
The void of course period, when the Moon makes no further major aspect before leaving a sign, is used in electional work rather than in natal reading.
The house, and the birth time problem
The lunar house shows where security is sought and where domestic habit settles. A Moon in the sixth house attaches to routine and work; the same Moon in the ninth attaches to travel and study. Neither can be determined without a birth time, and because the Moon itself is time-sensitive, the two uncertainties compound.
Where the time is genuinely unrecorded, it is more honest to give the range of possible lunar signs for that day than to pick one and read it with confidence.
Questions people ask about this
How often does the Moon change sign?
About every two and a half days, so it completes the zodiac in roughly twenty-seven and a third days.
Do I need a birth time for my Moon sign?
Often, yes. On days when the Moon changes sign the answer depends on the hour, and the house always requires a time.
Can the Moon be retrograde?
No. Neither luminary retrogrades. The Moon's equivalent cycle is its phase relative to the Sun.
What are the Moon's dignities?
It rules Cancer and is exalted in Taurus, with detriment in Capricorn and fall in Scorpio.