Planetary hours

One of the oldest and most concrete tools in traditional timing: every hour of the day belongs to one of the seven classical planets. Unlike clock hours, these are not equal in length, and the day starts not at midnight but at sunrise.

The day begins at sunrise

In this system a "day" starts when the Sun rises, not at 00:00. That means a different boundary from the calendar: 4 a.m. on Tuesday still belongs to Monday's night.

The hours are unequal

Daytime (sunrise → sunset) is divided into twelve equal parts. Night (sunset → next sunrise) into twelve of its own.

In summer the day is long and the night short, so summer day-hours run longer than 60 minutes and night-hours shorter. In winter it reverses. Around the equinoxes both approach 60 minutes.

An example: Istanbul, 16 September 2026. Sunrise 06:50, sunset 19:17. Daytime lasts 12 hours 27 minutes; divided by twelve, each planetary hour is about 62 minutes.

The ruler of the day

Each day has a ruler, and the first planetary hour of that day belongs to it. The mapping still survives in the names of the days — French mardi (Mars), vendredi (Venus); English Saturday, Sunday, Monday:

The Chaldean order

After the first hour the ruler changes every hour, always following the same sequence — the Chaldean order, which lists the planets by apparent slowness, from slowest to fastest:

Saturn → Jupiter → Mars → Sun → Venus → Mercury → Moon → (repeat)

Applying a seven-step cycle to 24 hours produces a small elegance: if a day's first hour is Mercury, the first hour 24 hours later lands on Jupiter — the next day's ruler. The order of the weekdays falls out of that arithmetic.

Example: Wednesday in Istanbul

Wednesday's ruler is Mercury. Sunrise 06:50, each day-hour about 62 minutes:

As you can see, a Mercury hour comes round more than once a day — every seven hours.

Traditional uses

• Mercury hour — correspondence, contracts, meetings, study
• Venus hour — purchases, agreements, art, meeting people
• Jupiter hour — expansion, applications, official business
• Sun hour — visibility, dealing with authority
• Moon hour — home, moving, family, daily routine
• Mars and Saturn hours — traditionally considered harsh; not favoured for new beginnings

In Moon Compass

The app checks whether a suitable window contains the preferred planetary hour and, if it does, shows the exact sub-range — for example "Mercury hour 14:06–15:08". Within a nine-hour window you can see the single best hour.

In polar regions the Sun sometimes does not rise or set at all. There the app skips the planetary hour criterion silently rather than inventing a value.