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Planetary Hours Calculator

Chaldean planetary hours for any city and date: the ruler of the day, exact sunrise and sunset, and 24 unequal hours with their ruling planets.

What planetary hours are

Daylight is divided into 12 equal parts and the night into 12 more. Those hours are almost never 60 minutes long: in June in London a daytime hour runs about 82 minutes while a night hour is about 38. The closer to the pole and to the solstice, the wider the gap. That is why the boundaries are counted from actual sunrise and sunset rather than from midnight.

The Chaldean order

The hours are ruled by the seven visible lights in order of decreasing apparent speed: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. The sequence loops, so the Moon is followed by Saturn again. Taken every 24 hours, the same sequence produces the familiar order of the weekdays.

The day ruler and the first hour

The first hour after sunrise belongs to the planet the day is named after: Monday to the Moon, Tuesday to Mars, Wednesday to Mercury, Thursday to Jupiter, Friday to Venus, Saturday to Saturn, Sunday to the Sun. The rest follow the Chaldean loop. The astrological day starts at sunrise, so before dawn the previous day is still running.

What they are used for

Planetary hours belong to electional astrology, where the timing of an action is chosen deliberately: money talks are often set in an hour of Jupiter or Venus, a decisive move in an hour of Mars, paperwork in an hour of Mercury. This is not a forecast but a way to match the timing to the nature of the task.

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What a planetary hour is

Planetary hours are an ancient division of the day where daylight is split into twelve equal parts and the night into another twelve. Such hours almost never equal sixty minutes: in summer the day hour is longer than the night hour, in winter it is the other way round.

Each hour is ruled by one of the seven planets in the fixed Chaldean order: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. The first hour of the day always belongs to the planet the weekday is named after, and every other hour follows from it.

  • •Twelve day hours from sunrise to sunset
  • •Twelve night hours from sunset to the next sunrise
  • •Exact start time and length of every hour for your city

Where the planetary order comes from

The Chaldean order lists the planets by apparent speed, from the slowest to the fastest. Walking that order hour by hour around the circle, the first hour of the next day lands on the planet of the next weekday automatically. That is where the names of the days come from in most European languages.

It is not a coincidence but the logic built into the system: Sunday belongs to the Sun, Monday to the Moon, Tuesday to Mars, Wednesday to Mercury, Thursday to Jupiter, Friday to Venus, Saturday to Saturn.

How planetary hours are used

The hour is matched to the nature of the task. Mercury for negotiation, paperwork, study and anything written. Venus for creative work, dates and buying things for yourself. Mars for sport and decisive action. Jupiter for approaching management, legal matters and anything that needs weight behind it.

The Sun suits public speaking and whatever should be noticed, the Moon suits home and family matters, Saturn suits working with limits, calculations and long commitments. A Saturn hour is not evil in itself, it is simply not for fun.

  • •Saturn: structure, discipline, long commitments
  • •Jupiter: law, money, approaching people above you in rank
  • •Mars: sport, competition, decisive action
  • •Sun: visibility, leadership, presentations
  • •Venus, Mercury, Moon: relationships, communication, home

Why your city has its own hours

The length of an hour depends on when the Sun rises and sets in that particular place. In Kyiv a June day hour runs about 85 minutes, in December about 40. A table computed for another city or another date simply does not apply.

The calculator takes the coordinates of the chosen city, computes the real sunrise and sunset for the date and builds both tables, day and night. For polar latitudes, where the Sun may not set at all, it shows a warning instead of inventing values.

Planetary hours: common questions

Why are the hours not 60 minutes long?
Because day and night are divided separately: daylight into 12 parts and darkness into 12. They come out equal only twice a year, at the equinoxes.
Where does the day ruler come from?
From the weekday. The first hour after sunrise belongs to that day's planet, and the rest follow the Chaldean loop.
What about cities with polar day?
During polar day or night the Sun never crosses the horizon, so the hours have no boundaries. The calculator says so and skips the computation for such a date.
Is daylight saving time taken into account?
Yes. The UTC offset comes from the timezone database for that specific date, so DST transitions are covered.
How accurate are sunrise and sunset?
The moment is computed with Swiss Ephemeris using standard refraction, with the disc centre at -0°50'. The difference from common tables is usually within two minutes, which does not matter for planetary hours.
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