Free Tool · Chaldean Order
Planetary Hours Calculator
Which planet rules this hour, right now, for your location — in the ancient Chaldean order.
Sunrise and sunset are computed for your coordinates with the NOAA solar algorithm (accurate to about a minute). Nothing is sent to a server — the calculation runs entirely in your browser.
What are planetary hours?
Planetary hours are an old way of dividing the day that pays no attention to the clock on the wall. Instead of twenty-four equal sixty-minute hours, the daylight — from sunrise to sunset — is split into twelve equal parts, and the night — from sunset to the next sunrise — into twelve more. Because daylight and darkness are rarely the same length, these "temporal" hours stretch and shrink with the season and your latitude. A summer day-hour can run past seventy minutes while the night-hours shorten to forty; in winter the proportions flip.
Each of these twenty-four hours is assigned a ruling planet — one of the seven the ancients could see move: Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon. The system is at least two thousand years old and underlies a great deal of traditional electional astrology, the art of choosing a favourable moment to begin something.
The Chaldean order explained
The hours are not handed out at random. They follow the Chaldean order — the seven planets ranked by how slowly they appear to move against the background stars, from the most sluggish to the swiftest:
Walk down that list one step per hour and, when you reach the Moon, start again at Saturn. The first hour of any day begins at sunrise and is ruled by the planet of that weekday; every following hour takes the next planet in the sequence.
Why it names the days of the week
Here is the part most calculators skip — and the real link between the Chaldean order and the calendar. A day holds twenty-four hours, and there are seven planets. Twenty-four divided by seven leaves a remainder of three, so each new sunrise lands three places further along the Chaldean order than the last. Begin with the Sun and step three at a time around the circle of seven and you get Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn — which is exactly Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday. The names of the days of the week are simply the rulers of their first hour. Spanish martes (Mars), miércoles (Mercury) and viernes (Venus) still wear the planets openly; English hides them behind Norse gods, but the order is the same.
How planetary hours are calculated
The whole system rests on two moments: your local sunrise and your local sunset. This calculator finds them for your exact coordinates using the NOAA solar position algorithm, the same equations published by the U.S. National Oceanic and Atmospheric Administration, which are accurate to roughly a minute.
From there the arithmetic is simple:
- Measure the daylight (sunset minus sunrise) and divide it by twelve — that is the length of one day-hour.
- Measure the night (next sunrise minus sunset) and divide by twelve — that is one night-hour.
- The first day-hour starts at sunrise, ruled by the weekday's planet; each later hour advances one step in the Chaldean order.
Because the two halves are measured separately, day-hours and night-hours differ in length on every date except the equinoxes. The dial above shows the day across its top half and the night across the bottom, with the planet of each hour and a marker for the hour you are in now.
How to use this calculator
- Set your place. Start typing your city and pick it from the list, or tap “Use my exact location”. Your time zone — and daylight saving — is handled automatically.
- Read the panel at the top. It names the planet ruling right now, the window it covers, how long it lasts, and when it changes over.
- Look ahead. Step the date forward or back to see the hours for any day, and the full day-and-night table beside the dial.
Which planet for love, money or work?
In the electional tradition, each planet governs its own kinds of undertaking, and a moment is chosen by matching the work to the hour. These are the customary associations — old craft, not a promise of results:
| Planet | Traditionally chosen for | |
|---|---|---|
| ☉ | Sun | Success, vitality, leadership, dealings with people in authority |
| ☽ | Moon | Home, family, travel, the public, anything that ebbs and flows |
| ♂ | Mars | Action, courage, competition, hard physical effort |
| ☿ | Mercury | Messages, study, writing, trade, short journeys |
| ♃ | Jupiter | Growth, money, law, generosity, asking a favour |
| ♀ | Venus | Love, friendship, beauty, art, reconciliation |
| ♄ | Saturn | Discipline, patience, endings, property and land, the long game |
Frequently asked questions
What planet rules the current hour?
It changes through the day. This calculator shows the current ruling planet at the top, updated live for your location — the planet governing the temporal hour you are in right now, in the Chaldean order.
How long is a planetary hour?
Rarely sixty minutes. Daylight is divided into twelve equal parts and night into twelve, so an hour's length depends on the season and your latitude: short winter days give short day-hours and long night-hours, and the reverse in summer. Only near the equinox is each close to sixty minutes.
What is the Chaldean order of the planets?
Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon — the seven classical planets arranged from slowest to fastest as they appear to move against the stars. The hours follow this sequence, repeating after the Moon back to Saturn.
How do planetary hours make the days of the week?
Step one planet along the Chaldean order for each of the twenty-four hours and you advance three places by the next sunrise, because 24 divided by 7 leaves 3. Starting from the Sun you get Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn — Sunday, Monday, Tuesday and so on. The weekday names are the planetary hours written large.
How do you calculate planetary hours by hand?
Find your local sunrise and sunset. Divide the daylight into twelve equal day-hours and the night into twelve night-hours. The first day-hour begins at sunrise and is ruled by the planet of the weekday; each following hour takes the next planet in the Chaldean order.
Which planetary hour is best for love, money or work?
Traditionally, Venus hours are chosen for love and beauty, Jupiter and Sun hours for money and success, Mercury hours for messages, study and trade, and Mars hours for action and contests. These are old electional associations, not guarantees.
Do planetary hours change with my location?
Yes. They are built from your local sunrise and sunset, which depend on longitude, latitude and the date, so the hours and their boundaries differ from one city and day to the next.
How accurate is this calculator?
The sunrise and sunset are computed with the NOAA solar algorithm, accurate to about a minute. The planetary-hour rulers follow the standard Chaldean rule. Whether the hours carry the influence astrologers ascribe to them is a matter of tradition, not something this tool claims to prove.