Planetary hours: how to calculate them step by step

Planetary hours are a traditional way of dividing the day into twelve daylight and twelve night periods, each assigned to one of seven classical planets. This page shows how to calculate planetary hours with nothing more than a sunrise time, a sunset time and a fixed list of seven names. The method is old, simple and entirely arithmetic.

What planetary hours are

In the tradition described in the Wikipedia article on planetary hours, the period from sunrise to sunset is split into twelve equal parts, and the period from sunset to the next sunrise is split into twelve more. Because the length of daylight changes through the year, these hours are unequal: a day hour and a night hour are rarely sixty minutes each. Each hour is assigned a planet by the Chaldean order, Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, repeating in a cycle. The first hour of each day belongs to the planet that rules that weekday.

Step by step

1. Find sunrise and sunset for your place and date, and sunrise for the following day.
2. Divide the time from sunrise to sunset by 12. This is the length of one day hour.
3. Divide the time from sunset to the next sunrise by 12. This is the length of one night hour.
4. Name the weekday ruler: Sunday Sun, Monday Moon, Tuesday Mars, Wednesday Mercury, Thursday Jupiter, Friday Venus, Saturday Saturn.
5. Give hour 1 to that ruler, then follow the Chaldean order for every later hour, wrapping from Moon back to Saturn.
6. Number the hours 1 to 24 across day and night. Hour 13 is the first night hour and continues the same cycle without a break.

A worked example

Take a Thursday. The weekday ruler is Jupiter. The Chaldean list, counting from zero, is Saturn 0, Jupiter 1, Mars 2, Sun 3, Venus 4, Mercury 5, Moon 6. The rule is: ruler(h, weekday) = CHALDEAN[(idx(dayPlanet) + h) mod 7], where h starts at 0 for hour 1. For Thursday, idx is 1.

• Hour 1 (h = 0): index 1, Jupiter.
• Hour 2 (h = 1): index 2, Mars.
• Hour 3: Sun. Hour 4: Venus. Hour 5: Mercury. Hour 6: Moon.
• Hour 7 (h = 6): (1 + 6) mod 7 = 0, Saturn.
• Hour 8 (h = 7): (1 + 7) mod 7 = 1, Jupiter again.
• Hour 12 (h = 11): (1 + 11) mod 7 = 5, Mercury, the last daylight hour.
• Hour 13 (h = 12): 13 mod 7 = 6, Moon, the first night hour.
• Hour 24 (h = 23): 24 mod 7 = 3, Sun.

The next hour would be h = 24, and (1 + 24) mod 7 = 4, which is Venus. That matches Friday's ruler, so the cycle closes by itself. For length, imagine, purely as an illustration, eight hours between sunrise and sunset: 480 minutes divided by 12 gives 40-minute day hours.

Common mistakes and honest limits

• Using sixty-minute hours. Traditional planetary hours are unequal; only the equinox comes close to equal ones.
• Starting the day at midnight. The planetary day begins at sunrise, so an early-morning hour before sunrise belongs to the previous weekday.
• Breaking the cycle at sunset. Night hours continue the Chaldean order from hour 12.
• Mixing up the list order with the weekday order. The Chaldean order is Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon; the weekdays follow a different pattern.
• Treating the result as more than a tradition. A planetary hour is a symbolic timetable. No promise is made about any outcome.

How Luckwell builds it

Luckwell does not ask for your location or the time of sunrise, so the sigil does not use the hourly cycle itself. It uses the first link in the chain: the weekday ruler, taken from the same list of seven. When the weekday ruler differs from the planet of the chosen intention, it gives the secondary ring colour, which is why a sigil for luck made on a Monday differs from one made on a Thursday. A sigil made on its planet's own weekday is what Luckwell calls an 'own day'. Each planet is also tied to a kamea order, for example Jupiter to the 4×4 square described on the Jupiter kamea page. On the site every planet ink is remapped to oxidised gold, with the traditional planet colour kept only as a faint tint; the hex values are Luckwell's design choice. Browse the rest of the archive for the other layers. When you are ready, forge your own sigil.

FAQ

Luckwell is for entertainment and self-reflection; a sigil is a focus for your own intention, not a promise about health, money or the outcome of any event; 16+.