Planetary Hours

What planetary hours are

Planetary hours divide daylight into twelve parts and night into twelve more, then assign each part to one of the seven classical planets in a fixed sequence. Because daylight is longer in summer, a planetary hour is not sixty minutes — it is a twelfth of that day's daylight, which can run from about forty minutes to eighty depending on the date and your latitude.

The calculator above uses real sunrise and sunset times for your location, which is the only way the scheme works properly.

The Chaldean order

The sequence never changes: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, and back to Saturn. This is the classical ordering of the planets by apparent speed, slowest to fastest.

The elegant part is what falls out of it. The first hour after sunrise is ruled by the planet the day is named for — Sunday's first hour by the Sun, Monday's by the Moon, Tuesday's by Mars (mardi), and so on. Run twenty-four hours forward through the Chaldean order from any day's first hour and you land exactly on the next day's ruler. The seven-day week and the planetary hours are the same system.

What each hour is traditionally used for

• Sun — anything to do with authority, visibility or being seen well.
• Moon — domestic matters, travel by water, anything involving the public.
• Mars — physical effort, competition, surgery in the older texts, confrontation.
• Mercury — writing, negotiation, study, commerce, sending the message.
• Jupiter — asking for something. Loans, favours, legal matters, expansion.
• Venus — approaching someone, art, reconciliation, anything you want received warmly.
• Saturn — endings, boundaries, long-term structures, tasks needing patience.

Using it without overcommitting

The realistic use is narrow: pick one recurring task and put it in its hour for a month. Send difficult emails in a Mercury hour, ask for things in a Jupiter hour. It is one of the few traditional timing systems that costs nothing to test, because you are not avoiding anything — you are only choosing between times you were going to act anyway.

Location matters

Sunrise and sunset are local, so the hours are too. Near the poles in midsummer or midwinter the scheme degrades — with no sunrise there is no first hour — which is a limitation the medieval sources never had to deal with.