In the context of natal astrology, each of us is born during a particular "planetary hour," which can offer important information in delineating the birth chart. In electional astrology, planetary hours can assist in finding a favorable time to engage in a particular type of activity. In predictive astrology, the Persians made use of planetary hours as "lord of the orb" when interpreting the annual solar return for individuals. In horary astrology, we pay special attention to the planetary hour of the moment the chart is cast to help determine whether it is "radical" and able to give a proper answer to our question. To quote from my most recent book, Horary Astrology: The Theory and Practice of Finding Lost Objects: (Llewellyn, 2021):

"The lord of the hour thus serves as a bridge between the promise of the birth chart and the issues that preoccupy the querent's mind at the time of the query. For example, if Mercury were the planetary hour of the horary chart, then the winged planet would serve as the link between the significations of Mercury in the birth chart and the querent's current concerns. In other words, Mercury as current hour lord would 'activate' its natal house rulerships, placement and aspects and give them prominence in the querent's mind, thereby prompting the related horary question."

For those unfamiliar with the concept, the idea of planetary hours probably originated with the Babylonians, who assigned each hour of the day to one of the classical seven visible planets in Chaldean order from the slowest to the fastest: Saturn, Jupiter, Mars, Sun, Venus, Mercury, and Moon. Nowadays we divide the day into 24 hours, each of exactly 60 minutes in duration. Ancient astrologers, however, divided the 24-hour day into daytime and nighttime, and they further divided the periods of daylight and darkness into 12 "hours" each. The duration of each such "hour" was not the uniform 60 minutes that we use today, but rather it depended on the total number of hours of daylight for daytime hours and darkness for nighttime hours.

The planetary hours gave rise to the names of the days of the week. If we start at sunrise on the first day of the week ("Sun day") and assign the Sun to the first hour of the first day, we call that day "Sun day." Twenty-four hours later (on the second day) the Sun will rise in the hour of the Moon, giving us "Moon day." Another twenty-four hours later (on the third day) the Sun will rise during a Mars hour, giving us "Tuesday;" a day later, the Sun will rise during a Mercury hour ("Wednesday"); and so on until on the seventh day the Sun rises during a Saturn hour, a "Saturn day."

The accompanying tables list the sequence of planetary hours on the various days of the week. The most important planet is the one that rules the specific hour when you plan to do something. Also significant are the planets the rule the 24-hour day period (starting at sunrise) and, for nighttime activities, the planet that rules the hour of sunset should be taken into account.

Planetary Hours of Daylight (Sun Above the Horizon)

Planetary Hours of Nighttime (Sun Below the Horizon)

To illustrate the use of these tables, let's take a concrete example. I am writing this at 8:30 on a Saturday morning at my home in Connecticut. Using the program SolarFire, I generated the accompanying list of planetary hours specifically for my location. If you do an internet search, you can find apps for smartphones and websites that will generate such a list for your own location. Note that 24-hour days are calculated from sunrise to sunrise rather than as calendar days.

On December 12, 2020 at my location, the Sun rose at 7:14 in the morning. Because it is a Saturday, the planet Saturn rules the first hour of the day, which starts at sunrise. I happen to be writing at 8:30 am, which is during the second hour of the day, a Jupiter hour (from 7:59 am to 8:44 am). This is a favorable time to do some writing because Saturn (ruler of the day) signifies discipline and serious thought, and Jupiter has to do with learning, teaching, and expanded horizons. Furthermore, on this date (December 12th) the Sun is passing by transit through the sign Sagittarius, ruled by Jupiter, which gets an extra boost of solar vitality as the Sun traverses Jupiter's sign from November 21st to December 21st each year.

In addition, Jupiter is favorably situated in my natal chart, so that by acting during a Jupiter hour, I am making use of the positive potential of my birth chart. If Jupiter were afflicted in my natal chart, I would need to adjust my activity accordingly and take into account any negative potential signified by an afflicted Jupiter or the possibility of impediments to my work during this hour.

In fact, Jupiter by transit on December 12, 2020 lies between two difficult planets, Pluto and Saturn in Capricorn, which is the zodiacal sign of Jupiter's fall (opposite his sign of exaltation), suggesting that writing during a Jupiter hour on this particular date may require lots of hard work and not go as smoothly as I would like. We cannot assume that because Jupiter is generally a benefic planet it will always produce trouble-free results.

As the above example suggests, the wise use of planetary hours requires a careful consideration of several factors, which I will enumerate as a series of questions:

• What is the condition of the planetary hour ruler in your birth chart? If it is dignified, well-aspected, and occupies or rules favorable houses, then activities of the nature of the planet should do well during its hour. If it is afflicted, debilitated, lacking dignity, or occupies or rules potentially difficult houses, a note of caution is indicated.
• Which planet rules the sunrise prior to the planetary hour? That is, which planet rules sunrise of the 24-hour period in which the planetary hour falls? How does the "day ruler" interact with the planetary hour ruler in your birth chart and by current transit?
• If an activity is planned for a nighttime hour, which planet rules the hour of sunset prior to the planetary hour in question? How does the "nighttime ruler" interact with the planetary hour ruler in your birth chart and by current transit?
• What current transits is the planetary hour ruler involved in? What is its current state of dignity or debility in the heavens? It may be problematic to engage in activities during the planetary hour of a seriously afflicted planet.
• What is the zodiac sign that the Sun is currently transiting? The Sun as the vital force in our solar system gives an extra boost of energy to the ruler of the sign through which it passes.
• What is the nature of the planetary hour ruler and what type of activities does it naturally foster or obstruct? For example, you might not want to do something secretive or behind the scenes during a Sun hour because the Sun tends to illuminate and loves public attention.

The following is a list of some typical keywords related to activities and themes linked to the nature of the planetary hour ruler:

• Sun: Sunday (beginning at sunrise and for the next 24 hours), Sun also rules Wednesday's nighttime hours starting at sunset on Wednesday, the sign Leo, prominence, publicity, authority, influence, power, father figures, dignity, the life force, spiritual attainment
• Moon: Monday (beginning at sunrise and for the next 24 hours), Moon also rules Thursday's nighttime hours starting at sunset on Thursday, the sign Cancer, nurturing, caring, mother figures, nourishing, sheltering, emotions, milk, liquids, short journeys, changes, dealings with the public
• Mars: Tuesday (beginning at sunrise and for the next 24 hours), Mars also rules Friday's nighttime hours starting at sunset on Friday, the signs Aries and Scorpio, warriors, assertion, aggression, martial arts, forcefulness, impulsiveness, muscle power, cutting, fire, iron, machinery, competition, drive, activity, combat, conflict, initiative, the "lesser malefic," which is more problematic when the Sun is above the horizon
• Mercury: Wednesday (beginning at sunrise and for the next 24 hours), Mercury also rules Saturday's nighttime hours starting at sunset on Saturday, the signs Gemini and Virgo, intellect, cleverness, cunning, shrewdness, trickery, dexterity, gymnastics, communication, messages, reporting, commerce, sales, speaking, writing, travel, transit, information technology, attention to detail, literary and scientific pursuits, the nervous system
• Jupiter: Thursday (beginning at sunrise and for the next 24 hours), Jupiter also rules Sunday's nighttime hours starting at sunset on Sunday, the signs Sagittarius and Pisces, wisdom, justice, virtue, increase, growth, good fortune, benevolence, learning, teaching, wealth, philosophy, religion, the clergy, belief systems, a broad view, tolerance, expanded horizons, long journeys, over-indulgence, lust, the "greater benefic," which is even more favorable when the Sun is above the horizon
• Venus: Friday (beginning at sunrise and for the next 24 hours), Venus also rules Monday's nighttime hours starting at sunset on Monday, the signs Taurus and Libra, pleasure, dating, fun, sex, enjoyment, recreation, parties, socializing, hedonism, amusement, love, marriage, harmony, beauty, adornment, luxury, music, art, indulgence, the "lesser benefic," which is even more favorable when the Sun is below the horizon
• Saturn: Saturday (beginning at sunrise and for the next 24 hours), Saturn also rules Tuesday's nighttime hours starting at sunset on Tuesday, the signs Capricorn and Aquarius, gravity, seriousness, discipline, perseverance, reward for hard work, no-nonsense judgement, the "taskmaster," boundaries, structure, limitation, crystallization, tradition, old age, concentrated thought, in-depth understanding, agriculture, the "greater malefic," which is more problematic when the Sun is below the horizon

Let me offer a final word of caution. A wise person once said that astrology makes a good servant but a poor master. Planetary hours are a useful tool, but we must keep them in perspective so that we don't hesitate to live our lives without first checking whether the hour is favorable. An extreme example of the latter can be found in the Spanish proverb based on the malefic nature of Mars, the god of war: "En martes, ni te cases, ni te embarques, ni de tu casa te apartes:" "On Tuesdays (the day of Mars) don't get married, don't start out on a journey, and don't even leave your house!" Can you image a world in which everyone followed such advice?