Transits & cycles

Planetary hours

Also known as: planetary hoursplanetary hourplanetary hours calculatorplanetary hours todaychaldean orderchaldean planetary hourshours of the planetsunequal hoursseasonal hourstemporal hoursplanetary hours of the dayplanetary hours of the nightruler of the dayruler of the hourplanet of the dayweekday planetswhy days of the week are named after planetsvettius valens anthology book iplanetary hours calendar

Planetary hours are an ancient scheme in which the period from sunrise to sunset and the period from sunset to the next sunrise are each divided into twelve hours, and each hour is assigned to one of the seven planets in the Chaldean order. The first hour after sunrise belongs to the planet of the weekday.

Planetary hours are one of the oldest ways of tying the seven planets to the daily round. The idea goes back to the ancient world and was already familiar to astrologers of the Roman period, and Vettius Valens describes the planetary order in Book I of his Anthology. The scheme was then taken over by Persian, Arabic and medieval European authors, and it is still used by people who follow traditional astrology.

The order of the planets is the Chaldean order, from the slowest to the fastest as seen from the Earth: Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon. After the Moon the order starts again with Saturn, so that the sequence turns round and round like a wheel.

The day in this scheme runs from one sunrise to the next. The time between sunrise and sunset is divided into twelve equal parts, and the time between sunset and the following sunrise is divided into twelve more. These are seasonal hours, also called unequal or temporal hours, because their length changes with the season. In high summer at European latitudes a daytime hour lasts well over an hour and a night hour is short, and in midwinter it is the other way round. Only at the equinoxes are all twenty-four hours close to equal.

The first hour after sunrise belongs to the planet of the weekday, and each next hour belongs to the next planet in the Chaldean order. This explains the names of the days. If Saturday begins with an hour of Saturn, then the twenty-fourth hour counted on, the next sunrise falls three steps further along the order, on the Sun, and so the next day is the day of the Sun. In the same way Monday belongs to the Moon, Tuesday to Mars, Wednesday to Mercury, Thursday to Jupiter and Friday to Venus. The Romance languages keep these links visible, for example in French mardi, mercredi, jeudi and vendredi, and the English Sunday, Monday and Saturday show them too.

In the tradition each planet has its own range of significations, such as the Sun for authority and the Moon for the body and for change, and the hour is said to carry something of its ruler. This is a way of describing the character the ancients gave to the planets, and it is not a rule for choosing when to do things.

Planetary hours are a tradition, not a science. Nothing shows that an hour ruled by one planet or another affects what happens in it, and the scheme is not advice.

AstroSensus has free planetary hours for today or for any date, at a place you choose. Sunrise and sunset are calculated as almanacs publish them, with the upper limb of the Sun and standard refraction. The tool shows only the ruler of the day and the ruler of each hour, with the significations of the planet after Vettius Valens (Anthology I.1), and it states clearly that this is a tradition and not advice, so there is no best hour for anything. Inside the polar circles some days have no sunrise or no sunset, and for those days there are no hours.