Astronomical Timekeeping
Planetary Clock
Planetary Hours
Know which classical planetary hour rules right now — calculated from the true sunrise and sunset at your location.
A clean, precise reading of the day's planetary hours, the ruler of the day, and the current phase of the Moon.
What Are Planetary Hours?
An astronomical timekeeping system from classical antiquity.
Planetary hours divide daylight and night each into twelve parts. Because daylight and night change length through the year, these hours are unequal — they expand and contract with the seasons. Each hour is assigned to one of the seven classical planets, cycling in a fixed sequence known as the Chaldean order.
Planetary Clock computes these hours with astronomical precision, using your exact coordinates to find the real sunrise and sunset for any day — the same method used for centuries, with modern accuracy.
Common Questions
How accurate are the calculations?▾
Very precise. Planetary Clock uses your exact coordinates and astronomical algorithms to compute true sunrise and sunset, then divides day and night into the traditional unequal hours in Chaldean order.
Do I need any prior knowledge to use it?▾
No. The app shows the current planetary hour, the ruler of the day, and the Moon’s phase at a glance. Everything is read directly off the clock.
Does it work for my location and timezone?▾
Yes. The calculations are based on your geographic coordinates, so the hours and sunrise/sunset times are correct wherever you are.
Why are the hours different lengths?▾
Planetary hours are unequal by design: daylight is split into twelve hours and night into twelve, so each hour is longer or shorter depending on the season and your latitude.
Put the Sky on Your Wrist
Download Planetary Clock and read the day's planetary hours, the ruler of the day, and the phase of the Moon — anywhere.
Download on the App Store