Actually there are a lot of questions about time and calendars which can all be answered by reference to astrology, because the original purpose of astrology was to create a reliable method of measuring the passage of time. You see, the heavens themselves are the absolute clock by which we live our lives.
12 Hours. It is very interesting! There are 12 houses, and 12 signs – and similarly our clocks have 12 hours on them, even though there are really 24 hours in a day. It takes 2 hours for each of the 12 zodiac signs to move across the Eastern Horizon, to “rise.” Therefore you would think we should have 12 time units in our day, not 24, each of which is twice as long as our current hour. But the only reason we would think like this is because we have forgotten about the way ancient astrology divides the signs into smaller units.
The first smaller unit within a zodiac sign is, in fact, called hora. And this is where the word hour comes from! This hora division splits each zodiac into halves, giving one half to the Sun (Yang) and the other half to the Moon (Yin). 24 horas rise in the east every day. And this is why the day has 24 hours.
As to why the clock face has 12… 12 of the hours belong to the Sun (the daytime) and 12 belong to the Moon (the night). Thus the hora division of the zodiac creates the clock face that you’ve got on your walls and wrists.
– Vic DiCara