Planetary Hours Calculator
Planetary hours divide each day and each night into twelve unequal parts, each ruled by one of the seven classical planets. The calculator finds today's sunrise and sunset for your location and lists all 24 hours, with the planet ruling the hour you are in now.
How planetary hours work
The system comes from Hellenistic astrology and was used through the Middle Ages and Renaissance to choose times for actions. It has two parts.
- Unequal hours. The time from sunrise to sunset is split into 12 equal day hours, and the time from sunset to the next sunrise into 12 equal night hours. In summer the day hours are long and the night hours short; in winter the reverse. Only at the equinoxes are they close to 60 minutes each.
- The Chaldean order. The hours are given to the seven classical planets in order of their apparent speed, slowest first: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, then Saturn again, round and round.
The first hour after sunrise is ruled by the planet of the day: the Sun on Sunday, the Moon on Monday, Mars on Tuesday, Mercury on Wednesday, Jupiter on Thursday, Venus on Friday and Saturn on Saturday.
Where the names of the weekdays come from
The planetary hours explain the odd order of the week. A day has 24 hours, and 24 divided by 7 leaves 3. So if Saturn rules the first hour of one day, the 25th hour, the first of the next day, falls three planets further along the Chaldean list: Saturn, Jupiter, Mars, Sun. Saturday is followed by Sunday. Three more steps from the Sun give the Moon (Monday), then Mars (Tuesday), Mercury (Wednesday), Jupiter (Thursday) and Venus (Friday). The English names hide some of this because several days are named after the Norse equivalents (Tiw, Woden, Thor, Frigg), but French and Spanish keep it: mardi and martes for Mars, mercredi and miércoles for Mercury.
A worked planetary hours example
Suppose that in your city, on a Wednesday, the Sun rises at 6:00 and sets at 20:00. The day is 14 hours long, so each day hour lasts 70 minutes. The first hour, 6:00 to 7:10, belongs to Mercury (Wednesday's planet); the second, 7:10 to 8:20, to the Moon; the third to Saturn; and so on through the Chaldean order. The night is 10 hours long, so each night hour lasts 50 minutes, and the cycle continues from where the day hours stopped. At Thursday's sunrise the sequence lands on Jupiter, Thursday's planet, as it should.
Common planetary hours mistakes
- Using clock hours. Many simple lists start at midnight and use 60-minute hours. Traditional planetary hours start at sunrise and change length with the season.
- Ignoring your location. Sunrise and sunset depend on your latitude and longitude, so the hours in New York and Miami on the same day differ. Choose your city for accurate times.
- Starting the day at midnight. In this system the planetary day begins at sunrise, so the hours before dawn still belong to the previous day's night.
- Very high latitudes. Where the Sun does not rise or set (polar day or night), the hours cannot be defined; the calculator says so.
What people use them for
Traditional texts paired each planet's hour with its themes: Venus hours for friendship and art, Mercury hours for writing and study, Jupiter hours for generosity, and so on. Today people mostly use planetary hours to time rituals, journaling or a one card tarot reading. It is a symbolic timing practice; it cannot make any action succeed or fail. For the Moon's own rhythm, see the moon phase page and the void of course Moon calendar.
Questions
What are planetary hours?
A traditional way of dividing day and night into 12 unequal hours each, ruled in turn by Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon. The first hour after sunrise belongs to the planet of the day.
How long is a planetary hour?
It depends on the season and your latitude. A day hour is one twelfth of the time from sunrise to sunset, a night hour one twelfth from sunset to sunrise. In summer day hours can be well over 60 minutes.
What planetary hour is it now?
Open the calculator and pick your location: it highlights the current planetary hour and shows when it ends and which comes next.
Why does each day start with its own planet?
Because 24 hours run through the seven planets in the Chaldean order, and 24 divided by 7 leaves 3. Each new day's first hour lands three planets further on, which produces the order Sunday, Monday, Tuesday and so on.
Do planetary hours start at midnight?
Not in the traditional system. They start at local sunrise. Some apps use midnight and equal hours, which is a modern simplification.
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