Reading time: 11 minutes
Last updated: March 2026
Planetary hours divide each day into 24 unequal segments—12 daytime hours from sunrise to sunset, 12 nighttime hours from sunset to sunrise—each ruled by one of the seven classical planets in a fixed sequence called the Chaldean order. The first hour after sunrise on each day is ruled by the day's ruling planet (Sun on Sunday, Moon on Monday, Mars on Tuesday, and so on). The system was central to Hellenistic and Medieval astrology, and remains widely used today for timing rituals, decisions, and actions.
Historical Origins
The planetary hours system has roots in Babylonian astronomy and was formalized in the Hellenistic astrological tradition of the 2nd–4th centuries CE. The earliest clear exposition appears in Greek astrological literature, and the system is described extensively in texts like the Mathesis of Julius Firmicus Maternus (4th century CE) and referenced across the Hermetica and other philosophical traditions of late antiquity.
The system became central to both judicial astrology (electional astrology—timing important events) and magical practice during the Medieval and Renaissance periods. Grimoires like the Key of Solomon specify which planetary hour governs different types of ritual work. Magicians, physicians, and merchants alike consulted planetary hours tables before undertaking important business.
The naming of the days of the week is itself a direct product of the planetary hours system: the planet ruling the first hour of each day gave that day its name—a connection still visible in the English and Romance language names of the days (Sunday, Monday, Saturday; Lundi/Monday for Moon, Mardi/Tuesday for Mars, Mercredi/Wednesday for Mercury, Jeudi/Thursday for Jupiter, Vendredi/Friday for Venus).
The Chaldean Order
The planetary hours rotate through the seven classical planets in a fixed sequence known as the Chaldean order—named for the Babylonian astronomical tradition. The Chaldean order arranges the planets from slowest to fastest apparent motion as observed from Earth:
Saturn → Jupiter → Mars → Sun → Venus → Mercury → Moon
This sequence moves from the planet with the longest apparent cycle (Saturn, approximately 29.5 years) through to the shortest (the Moon, approximately 27.3 days). The planetary hours cycle continuously through this sequence: after the Moon comes Saturn again, then Jupiter, and so on indefinitely.
This order appears in multiple ancient contexts—not just planetary hours, but also in the traditional arrangement of the "heavenly spheres" in geocentric cosmology, where the Earth is surrounded by successive shells of the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn, each governing a domain of existence from most temporal to most eternal.
How to Calculate Planetary Hours
Calculating planetary hours requires knowing your local sunrise and sunset times for the day in question. These vary by location and date.
Step 1: Find your sunrise and sunset times. Use a weather app, astronomical almanac, or online tool for your specific location and date.
Step 2: Calculate day hours and night hours.
- Day duration = Sunset time − Sunrise time (in minutes)
- One planetary day hour = Day duration ÷ 12
- Night duration = 24 hours − Day duration (in minutes)
- One planetary night hour = Night duration ÷ 12
Note that planetary hours are not the same as clock hours—they are variable in length depending on the season and latitude. In summer, day hours are longer than 60 minutes and night hours are shorter; in winter, the reverse is true.
Step 3: Identify the day ruler. The planet ruling the first hour after sunrise is determined by the day of the week:
- Sunday: Sun
- Monday: Moon
- Tuesday: Mars
- Wednesday: Mercury
- Thursday: Jupiter
- Friday: Venus
- Saturday: Saturn
Step 4: Assign subsequent hours. Each subsequent hour moves to the next planet in the Chaldean order (Saturn → Jupiter → Mars → Sun → Venus → Mercury → Moon → Saturn → ...). Daytime hours run from hour 1 (sunrise) through hour 12 (before sunset). Nighttime hours run from hour 13 (sunset) through hour 24 (before the next sunrise).
Example: Saturday, finding the hours:
- Hour 1 (sunrise): Saturn
- Hour 2: Jupiter
- Hour 3: Mars
- Hour 4: Sun
- Hour 5: Venus
- Hour 6: Mercury
- Hour 7: Moon
- Hour 8: Saturn
- (and so on, cycling back through the Chaldean order)
The planet ruling the first hour of the next day will always be the correct day ruler for the following day. This mathematical regularity is what produced the 7-day week named for the planets—a cross-cultural invention that now structures civilization.
Day Rulers and Week Names
- Sunday — Sun: Identity, vitality, authority, success, and creativity. Good for leadership actions, visibility, and anything requiring confidence and radiance.
- Monday — Moon: Emotion, intuition, cycles, home, and memory. Good for emotional work, domestic matters, beginnings, and anything requiring sensitivity.
- Tuesday — Mars: Action, courage, conflict, and drive. Good for decisive action, competitive endeavors, physical activity, and confronting challenges.
- Wednesday — Mercury: Communication, commerce, learning, and travel. Good for writing, contracts, negotiations, sending correspondence, and intellectual work.
- Thursday — Jupiter: Expansion, abundance, legal matters, and growth. Good for business expansion, seeking opportunity, legal proceedings, and anything requiring good fortune.
- Friday — Venus: Love, beauty, pleasure, and art. Good for romantic matters, creative projects, social connections, and anything requiring harmony.
- Saturday — Saturn: Structure, discipline, restriction, and long-term work. Good for planning, establishing boundaries, serious commitments, and anything requiring endurance.
What Each Planet's Hour Means
The planetary hours are most useful not just by day but by specific hour. The first hour of the day has the strongest expression of the day ruler; subsequent hours offer their own qualities as the cycle moves through all seven planets.
Saturn Hour: Grounding, establishing structure, setting long-term plans, working with boundaries, protection, and binding. Good for serious study, agricultural work (traditional), signing binding agreements when durability is required. Less favorable for new beginnings or social interactions.
Jupiter Hour: Abundance, expansion, luck, philosophical inquiry, generosity, and healing. Good for financial decisions, seeking advancement, legal matters, teaching, and any endeavor where growth and good fortune are sought.
Mars Hour: Action, assertion, courage, physical activity, and conflict resolution. Good for beginning difficult tasks that require force of will, physical training, confronting enemies or challenges, surgery (in traditional medical astrology), and any endeavor requiring decisive action.
Sun Hour: Clarity, authority, visibility, success, and vitality. Good for presenting oneself to authority, making important decisions requiring clarity, leadership actions, and matters of the heart. The Sun hour on Sunday is particularly strong.
Venus Hour: Love, beauty, pleasure, art, and social harmony. Good for romantic overtures, creative work, social events, purchasing luxury items, and anything requiring charm and grace.
Mercury Hour: Communication, commerce, learning, trickery, and movement. Good for writing, all forms of communication, travel, commerce, teaching, and intellectual problem-solving.
Moon Hour: Intuition, emotion, memory, home, beginnings, and cycles. Good for beginning new projects (especially those requiring growth), emotional conversations, domestic matters, and anything requiring receptivity and adaptability.
Practical Applications
- Match the hour to the action. The most straightforward use: identify what you want to do, find the planet that governs it, and act during that planet's hour. Sending an important email: Mercury hour. Asking for a raise: Jupiter or Sun hour. Starting a new creative project: Venus or Sun hour.
- Combine day and hour for stronger timing. Acting during the Venus hour on a Friday (Venus day) amplifies the Venus energy. Saturn hour on Saturday is particularly strong for binding work, serious commitments, and long-term structure.
- Use the first hour of the day for setting intentions. The first planetary hour after sunrise (always the day ruler) is traditionally the strongest hour of the day. Morning rituals, affirmations, or important decisions made in this first hour carry the full quality of the day's energy.
- Avoid obvious mismatches. Starting a new romantic relationship during a Saturn hour (restriction, delay) or making a financial investment during a Mars hour (impulsive, conflict) are classical mismatches. This doesn't make the action cursed—but it removes the supportive timing.
- Use planetary hours for ritual work. This is the most traditional application: Hermetic and ceremonial magical traditions specify planetary hours for different types of ritual work, based on which planet governs the operation being performed.
Planetary hours are a simplified but accessible form of electional astrology—the branch of astrology dedicated to choosing the best time for undertaking important actions. Full electional astrology involves entire chart analysis for the chosen moment, but planetary hours offer a practical daily-level timing tool that doesn't require constructing a chart.
Historical practitioners didn't have smartphones. They had planetary hours tables. Medical procedures, legal documents, business ventures, marriages, and military campaigns were all timed using this system. The underlying principle—that different times carry different qualities—is exactly what all astrological timing work is built on.
Planetary Hours in Modern Practice
Planetary hours apps are widely available and automate the calculation completely—simply enter your location and the app displays the current planetary hour and what hours are coming next. This has made the practice more accessible than at any point in history.
Contemporary practitioners use planetary hours in several ways:
- Practical timing: Scheduling important meetings, sending significant communications, beginning new projects, or making financial decisions in aligned hours.
- Ritual timing: Ceremonial magicians, Wiccans, and folk practitioners continue to use planetary hours as the foundational timing framework for magical operations.
- Meditation practice: Some practitioners meditate on the qualities of each planet during its hour—using the hours as a contemplative framework for engaging with planetary archetypes throughout the day.
- Integration with natal chart: The hours of planets that are strongly placed or significant in the natal chart are particularly powerful for that individual. If Venus is your chart ruler, Venus hours carry special personal significance.
What the planetary hours system ultimately teaches is that time is not homogeneous. Not every moment is equally suited to every action. This is a fundamentally different relationship with time than the modern assumption that all hours are interchangeable units to be filled as efficiently as possible.
Working with planetary hours is a practice of attention—learning to sense the quality of a given moment, to align action with the current of time rather than swim against it. Whether approached practically or philosophically, this attunement to time's texture is one of the oldest forms of human wisdom.
Frequently Asked Questions
What time does the planetary day begin?
The planetary day begins at sunrise, not at midnight. The first planetary hour of the day always starts exactly at local sunrise. This is why you need to know your local sunrise time to accurately calculate planetary hours.
Are planetary hours the same in different traditions?
The Chaldean order and the day ruler system is consistent across Western astrological traditions (Hellenistic, Medieval, Renaissance, and modern). Vedic and Chinese astrology have their own time-division systems that differ in structure. Within the Western tradition, the core system is universal.
Does planetary hour override full natal chart timing?
Planetary hours are one layer of astrological timing—useful and practical, but not absolute. A challenging Saturn transit does not become positive simply because you act during a Jupiter hour. Planetary hours add nuance and practical timing guidance; they work within the larger context of a person's natal chart, transits, and progressions.
What happens at the equinoxes when day and night are equal?
At the equinoxes (approximately March 20 and September 22), day and night are of equal length, so day hours and night hours are both exactly 60 minutes long—the only time in the year when planetary hours correspond precisely to clock hours.
- Julius Firmicus Maternus, Mathesis (4th century CE; translated by Jean Rhys Bram, 1975)
- Robert Hand, Night & Day: Planetary Sect in Astrology (ARHAT Publications, 1995)
- Christopher Warnock, The Mansions of the Moon (Renaissance Astrology, 2010)
- Benjamin Dykes, Works of Sahl and Masha'allah (Cazimi Press, 2008)