Foundations
How are planetary hours calculated?
See how sunrise, sunset, location, weekday rulers, and the planetary sequence produce daytime and nighttime horas.
Myhora Editorial Team · Updated
Short answer
Planetary hours are calculated from local sunrise and sunset. The time from sunrise to sunset is divided into twelve equal daytime segments, and sunset to the next sunrise into twelve nighttime segments. The weekday ruler starts the sequence, followed by the traditional repeating order of Saturn, Jupiter, Mars, Sun, Venus, Mercury, and Moon.
The calculation in four steps
First, determine sunrise and sunset for the user’s coordinates and date. Second, divide the daylight interval by twelve. Third, do the same for sunset to the following sunrise. Finally, assign rulers, beginning with the weekday’s planet and continuing through the repeating sequence.
Because daylight varies, daytime and nighttime horas can have different lengths. A summer daytime hora at a high latitude may be much longer than a nighttime one.
Why location and date matter
Using a fixed 60-minute table ignores the astronomical boundaries that define the system. Reliable calculation therefore needs a timezone, geographic coordinates, and correct handling of the next day’s sunrise.
Myhora calculates these boundaries locally from the selected location. It then adds chart context separately; the astronomical schedule and the personal interpretation are not the same calculation.
A long summer day
If daylight lasts fifteen hours, each daytime hora lasts seventy-five minutes. If the night lasts nine hours, each nighttime hora lasts forty-five minutes. Both are valid within the same date and location.
Precision and edge cases
Sunrise definitions, polar-day conditions, timezone changes, and location accuracy can affect boundaries. Near a transition, allow a small practical margin instead of treating a single minute as absolute.
Related questions
Why do hora times change every day?
Sunrise and sunset shift, changing the length and boundaries of all twenty-four segments.
Which planet starts the day?
The traditional ruler of the weekday starts the first hora at local sunrise.
Does daylight saving time change the calculation?
It changes the displayed civil time, while the underlying boundaries still follow local sunrise and sunset.