What Are Planetary Hours? How Astrhora Calculates and Displays Them
What are planetary hours?
Planetary hours are a traditional way of dividing and interpreting time. Daylight and darkness are each split into twelve parts, making twenty-four planetary hours in a full cycle. These are not necessarily sixty-minute clock hours. Because sunrise and sunset change with the season and location, the duration of a planetary hour changes too. Summer daylight hours are usually longer and summer night hours shorter; winter reverses that pattern.
The traditional sequence uses seven celestial bodies: Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon. “Planet” is a historical astrological term here; the Sun and Moon are not planets in astronomy. The sequence continues from one hour to the next. The first daylight hour is associated with the weekday ruler: Sun on Sunday, Moon on Monday, Mars on Tuesday, Mercury on Wednesday, Jupiter on Thursday, Venus on Friday and Saturn on Saturday.
Historical background
It would be misleading to describe planetary hours as one unchanged system inherited directly from ancient Sumer. Mesopotamia had old traditions of observing and symbolizing celestial bodies, but clearer examples of the seven-day planetary week emerged later in the Hellenistic and Greco-Roman world. The tradition was interpreted in Islamic astronomical and astrological literature and later in medieval and Renaissance Europe. Astrhora presents this cultural history through a modern digital tool.
The seven symbolic themes
The Sun is associated with will and visibility; the Moon with emotion and adaptation; Mercury with knowledge and communication; Venus with relationships and beauty; Mars with action and courage; Jupiter with growth and opportunity; and Saturn with discipline and durable structures. Every theme also has a caution: Martian energy can become haste, Venusian harmony can become avoidance, and Jupiterian optimism can become excess. Rather than label a planetary hour simply good or bad, consider how its symbolic character relates to an activity.
How are the hours calculated?
Astrhora first obtains sunrise and sunset for the chosen place and date. It divides the time from sunrise to sunset into twelve equal daylight hours. It divides the time from sunset to the next sunrise into twelve equal night hours. For example, a ten-hour day produces fifty-minute daylight hours, while a fourteen-hour night produces seventy-minute night hours. Each segment is assigned the next body in the traditional seven-body sequence.
For the selected calendar date, daylight hours run from that day’s sunrise to sunset, and night hours run from that sunset to the next sunrise. The warm left dial shows daylight hours 1–12; the blue right dial shows night hours 13–24. Daylight and night interpretations both use their respective sections of the selected weekday’s row. After midnight, the previous calendar date’s night hours continue until sunrise.
Astrhora makes one WeatherAPI astronomy request for the selected date. It calculates the following sunrise locally to end the night interval; if the service is unavailable, it also estimates the selected day’s solar times locally. Hour intervals start at astronomical sunset without an added precaution period. Astrhora is not intended for prayer-time calculations. At high latitudes, sunrise or sunset may not occur on some dates, so a normal twelve-part calculation may be unavailable.
How do I use Astrhora?
Open Location, select a country, then search for a city, district or settlement and choose the correct result. Choose a date and press Show. Location and date searches need no sign-in; Google sign-in is requested only to set an alarm. The two connected dials display the twelve daylight and twelve night hours. The large center circle highlights the currently relevant hour, its planetary body and its position in the sequence.
Tap a planet or hour number to open its interpretation card. The card shows the starting and ending clock times, planetary ruler and traditional interpretation. Share creates an image with the place, date, time range and Astrhora logo. Set Alarm can remind you of a selected planetary hour; in the current web version the browser tab must remain open for the notification to work.
Interpretations and limits
Qualities attributed to planetary hours are historical and cultural interpretations. Describing an hour as favorable or unfavorable does not mean that it scientifically predicts outcomes. Astrhora presents this material for exploration and personal planning; it does not replace professional medical, financial or legal advice.
Times are shown in the selected place’s time zone, so changing the place can change sunrise, sunset and the hour boundaries. For exact prayer times, use the official local timetable. The interface, this guide, and all 168 detailed hour interpretations are available in thirteen languages.
Calculation and data sources
WeatherAPI Astronomy API · NOAA Solar Calculator · Freie Universität Berlin: Theōn hemerai