Calculate Planetary Hours Calculator

Determine the planetary hours for any date and location to understand the ruling influences.

Hour Type	Hour #	Start Time	End Time	Ruling Planet

Planetary Hours for the selected date and location.

What is Calculate Planetary Hours?

The practice to calculate planetary hours involves dividing the time between sunrise and sunset (day) and sunset and sunrise (night) into 12 equal portions each. These portions are not necessarily 60 minutes long; their duration varies with the season and latitude. Each of these “hours” is traditionally believed to be ruled by one of the seven classical planets (Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon) in a specific sequence known as the Chaldean order.

To calculate planetary hours means finding the exact start and end times of these 12 day hours and 12 night hours and identifying the ruling planet for each. This system was used in ancient and medieval astrology to determine auspicious times for various activities, based on the nature of the ruling planet.

Anyone interested in traditional astrology, horary astrology, or electional astrology might want to calculate planetary hours to align their actions with perceived cosmic influences. It’s also a fascinating study for those interested in the history of timekeeping and astrology.

A common misconception is that planetary hours are always 60 minutes long. In reality, only near the equinoxes at the equator do they approach 60 minutes. Day hours are longer in summer and shorter in winter, while night hours are the opposite.

Calculate Planetary Hours Formula and Mathematical Explanation

The process to calculate planetary hours involves several steps:

1. Determine Sunrise and Sunset Times: For the given date and location (latitude and longitude), calculate the precise times of sunrise and sunset. This requires astronomical formulas considering the Earth’s tilt and orbit.
2. Calculate Day and Night Duration:
   • Day Duration = Time between Sunrise and Sunset.
   • Night Duration = Time between Sunset and the next Sunrise (or 24 hours – Day Duration).
3. Calculate Hour Length:
   • Length of one Day Hour = Day Duration / 12.
   • Length of one Night Hour = Night Duration / 12.
4. Determine Hour Start/End Times:
   • The first day hour starts at sunrise. The subsequent day hours start at the end of the previous one.
   • The first night hour starts at sunset. The subsequent night hours start at the end of the previous one.
5. Identify Ruling Planets: The ruling planet of the first hour of the day (starting at sunrise) is the planet associated with that day of the week (e.g., Sun for Sunday, Moon for Monday). Subsequent hours follow the Chaldean order of planets: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, and then repeating.

Variables involved in the calculation of planetary hours.

Variable	Meaning	Unit	Typical Range
Sunrise Time	The moment the upper limb of the Sun appears on the horizon.	Time (HH:MM:SS)	Varies daily
Sunset Time	The moment the upper limb of the Sun disappears below the horizon.	Time (HH:MM:SS)	Varies daily
Day Duration	Time between sunrise and sunset.	Minutes or Hours	Varies (e.g., 6-18 hours)
Night Duration	Time between sunset and next sunrise.	Minutes or Hours	Varies (e.g., 6-18 hours)
Day Hour Length	Duration of one of the 12 day hours.	Minutes	Varies (e.g., 30-90 min)
Night Hour Length	Duration of one of the 12 night hours.	Minutes	Varies (e.g., 30-90 min)

Practical Examples (Real-World Use Cases)

Example 1: Summer Day in New York

Let’s say we want to calculate planetary hours for July 20th, 2024, in New York City (Latitude: 40.71, Longitude: -74.00). Assume sunrise is at 5:45 AM and sunset is at 8:15 PM (20:15).

• Day Duration: 8:15 PM – 5:45 AM = 14 hours 30 minutes = 870 minutes.
• Night Duration: 24 hours – 14 hours 30 minutes = 9 hours 30 minutes = 570 minutes.
• Day Hour Length: 870 / 12 = 72.5 minutes (72 minutes 30 seconds).
• Night Hour Length: 570 / 12 = 47.5 minutes (47 minutes 30 seconds).

If July 20th, 2024, is a Saturday, the first hour of the day (5:45 AM – 6:57:30 AM) is ruled by Saturn. The next by Jupiter, then Mars, and so on.

Example 2: Winter Night in London

Let’s calculate planetary hours for December 21st, 2024, in London (Latitude: 51.51, Longitude: -0.13). Assume sunrise is at 8:04 AM and sunset is at 3:54 PM (15:54).

• Day Duration: 3:54 PM – 8:04 AM = 7 hours 50 minutes = 470 minutes.
• Night Duration: 24 hours – 7 hours 50 minutes = 16 hours 10 minutes = 970 minutes.
• Day Hour Length: 470 / 12 ≈ 39.17 minutes (39 minutes 10 seconds).
• Night Hour Length: 970 / 12 ≈ 80.83 minutes (80 minutes 50 seconds).

If December 21st, 2024, is a Saturday, the first hour of the day (8:04 AM – 8:43:10 AM) is ruled by Saturn. The first hour of the night (3:54 PM – 5:14:50 PM) would be ruled by Jupiter (following the Chaldean sequence after the day hours). For more on rulers, see planetary rulers of the day.

How to Use This Calculate Planetary Hours Calculator

1. Enter Date: Select the date for which you want to calculate the hours.
2. Enter Latitude: Input the latitude of your location. Positive for North, negative for South.
3. Enter Longitude: Input the longitude of your location. Positive for East, negative for West.
4. Enter Timezone Offset: Input your local time’s offset from UTC in hours.
5. Calculate: The results will update automatically, or you can click “Calculate”.
6. Read Results: The calculator will show sunrise, sunset, day/night hour lengths, and a table with the start/end times and ruling planet for each of the 24 planetary hours.
7. Interpret: Use the ruling planet information for each hour to guide activities based on traditional astrological correspondences. For instance, Venus hours might be favored for social matters, Mercury for communication, etc. Learn more about using planetary hours.

Key Factors That Affect Calculate Planetary Hours Results

• Date: The date determines the Earth’s position in its orbit, affecting the declination of the Sun and thus the length of daylight.
• Latitude: Your north-south position greatly influences the length of day and night, especially as you move away from the equator. Higher latitudes experience more extreme variations.
• Longitude: Your east-west position affects the timing of local sunrise and sunset relative to UTC, but not the duration of day/night for a given latitude and date.
• Timezone: This is used to convert the calculated UTC times of sunrise/sunset and planetary hours to your local time. Incorrect timezone offset will give incorrect local times.
• Accuracy of Sunrise/Sunset Calculation: The entire system to calculate planetary hours depends on accurate sunrise/sunset times. Our calculator uses a standard algorithm, but atmospheric refraction can cause slight variations.
• Day of the Week: This determines the starting planet for the first hour of the day, setting the sequence for all subsequent hours. For the sequence, see the Chaldean order of planets.

Frequently Asked Questions (FAQ)

What are the seven classical planets?

They are Saturn, Jupiter, Mars, Sun, Venus, Mercury, and Moon, in the order of their apparent speed as seen from Earth (slowest to fastest, excluding Moon then Sun, then reverse).

Why are planetary hours not 60 minutes long?

Because the time between sunrise and sunset (and sunset to sunrise) is divided into 12 equal parts. This duration changes throughout the year and with latitude, so the length of each “hour” also changes.

How do I find my latitude and longitude?

You can easily find them by searching for your city or address on online map services or GPS tools.

Does the calculator account for Daylight Saving Time (DST)?

You need to input the correct timezone offset for the date you select, including any DST adjustments applicable for that date and location.

What is the Chaldean order?

It’s the sequence Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, believed to represent the planets arranged by their spheres from outermost to innermost relative to Earth in ancient cosmology.

Can I use planetary hours for any location?

Yes, you can calculate planetary hours for any location as long as you have the correct latitude and longitude.

What if I am very close to the poles?

Near the poles, during periods of 24-hour daylight or darkness, the concept of dividing day/night into 12 hours breaks down as sunrise or sunset might not occur. The calculator may not give meaningful results for extreme latitudes during these times.

How were planetary hours used historically?

They were used to choose auspicious times for activities, from medical treatments and planting crops to starting journeys or engaging in magical or alchemical work, aligning actions with the nature of the ruling planet. Get a primer on astrology basics.