Planetary hours divide daylight and darkness into twelve parts each, then assign the seven traditional planets in a repeating sequence.
Why an hour is not sixty minutes
Daylight runs from local sunrise to sunset and is divided by twelve; night runs from sunset to the next sunrise and is divided again. Except near the equinox, a daytime planetary hour and a nighttime planetary hour have different lengths.
The first hour belongs to the planet that rules the weekday. Continue through the traditional Chaldean order and the sequence produces the familiar order of weekday names.
How the system is used
Astrological and magical texts select hours whose planetary symbolism suits an activity: Venus for attraction and concord, Mercury for writing and exchange, Saturn for limits and endings. The hour is one elected factor, not a guarantee of outcome.
What to check in a handbook
A good guide states its planetary order, method for sunrise and treatment of daylight-saving time. If it prints fixed clock hours all year, it is describing a modern simplification rather than traditional unequal hours.
