What planetary days and hours are
Each day of the week is ruled by one of the seven classical planets, in the order still embedded in the languages around us. Sunday the Sun, Monday the Moon, Tuesday Mars, Wednesday Mercury, Thursday Jupiter, Friday Venus, Saturday Saturn. The day does not begin at midnight in this system but at sunrise, and the first hour belongs to the day's ruler.
The remaining hours are then filled by stepping through the Chaldean order — Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon — one planet per hour, looping continuously. Because the day ruler is placed at sunrise, the sequence happens to make each day's ruler match its name, which is exactly how the seven-day week was originally built from the sky.
How we compute it
We find the exact sunrise and sunset for your date and coordinates using sub-arcsecond astronomy (VSOP87/ELP via astronomy-engine), then divide the interval from sunrise to sunset into twelve equal temporal hours, and the interval from that sunset to the next sunrise into twelve more. Each hour's ruler is the Chaldean successor of the one before it, starting from the weekday ruler at sunrise.
Because temporal hours are one twelfth of the actual daylight, their length changes every day and varies enormously with latitude — roughly 58–59 minutes in London at the autumn equinox, but far shorter in midwinter or far longer at the summer solstice. The table prints each hour's real start and end in your local time so there is no arithmetic left for you to do.
What you get
After entering a date and place, the report shows:
- The planetary day and its ruler — which planet owns the whole day.
- Exact sunrise and sunset for your coordinates, in local and UTC time.
- Which day or night hour your chosen moment falls in, and the planet ruling it.
- The full 24-hour table: every temporal hour with its ruler, local start and end, and length.
How the hours are traditionally used
Electional astrology — the art of choosing start-times — teaches that you begin a task in the hour of the planet that rules its theme. Appointments, honours and public undertakings in a Sun hour; contracts, study, writing and errands in a Mercury hour; friendship, art and reconciliation in a Venus hour; courage, competition and difficult effort in a Mars hour; boundaries and long-term structure in a Saturn hour; growth and seeking favour in a Jupiter hour; and home, mothering and anything cyclical in a Moon hour.
The hours are also filtered by the day. An election traditionally wants the hour's ruler to agree with the day's ruler rather than fight it. This is a practical, low-stakes folk technique — a way of deliberately matching the shape of a task to a moment — rather than a claim that the clock decides your outcome.
A worked example: London, Thursday 1 October 2026
Thursday is Jupiter's day, so at sunrise — 06:01 UTC (07:01 BST) in London that morning — the first temporal hour belongs to Jupiter. Stepping the Chaldean order from there, the day hours run Jupiter, Mars, Sun, Venus, Mercury, Moon, Saturn, and the sequence then repeats. Sunset falls around 17:38 UTC, and each of the twelve daylight hours lasts about 58 minutes.
To see why the assignment is not a mere label, compare Friday 20 March 2026 in New York. Friday is Venus's day, so its sunrise hour is Venus — but from Venus the Chaldean order continues Mercury, Moon, Saturn, Jupiter, Mars, Sun, and so the thirteenth hour (the first hour of that night) lands on Mars.
The same rule that puts Jupiter at the head of a Thursday London morning is the one that hands a Friday New York nightfall to Mars: it is pure counting from a real sunrise, which is exactly what makes it reproducible.
What this tool does not claim
There are two competing ways to number the hours. We use the sunrise-start convention above (day begins at sunrise, hour 1 = the day's ruler). Some medieval sources instead begin the day at midnight and derive the hour ruler differently, which can shift a given clock-minute between two planets near the boundaries. There is no single 'correct' planetary hour; we state our convention so you can match or reconcile it with any grimoire or almanac.
Near the polar circles the Sun may not rise or set on a given date, which makes temporal hours undefined — the tool reports that honestly rather than inventing a division. And the meaning assigned to each planet's hour is traditional electional doctrine, not a measured effect. All computation runs locally; nothing is uploaded.
Where it sits next to other readings
The Void-of-Course Moon tracker is the other 'choose a moment' tool here and is purely lunar; planetary hours add the day-ruler and the hour structure. For natal work — where a planet sits in your own chart — see the natal and Traditional Chart tools; this page is about the sky's clock, not your birth chart.
Our method in one line
Sunrise and sunset solved for your coordinates from sub-arcsecond astronomy (VSOP87/ELP via astronomy-engine), twelve day and twelve night temporal hours divided equally, and rulers assigned by the Chaldean order stepping from the weekday ruler at sunrise. Reviewed by Dr. Amara Osei, Astronomy Reviewer.
Step by step
- 1
Enter any date and place
This is a clock, not a birth reading — use the form as 'date and location' for the day you want to inspect.
- 2
Find the day's ruler
The header names the planetary day and its ruler, anchored to the exact sunrise and sunset computed for your coordinates.
- 3
Locate your moment
The highlighted row tells you which temporal hour your chosen time sits in and which planet rules it.
- 4
Match task to hour
Tip: pick the hour of the planet whose theme fits your task — Mercury for a difficult email, Venus for making peace. Tip: prefer hours whose ruler agrees with the day's ruler.
Frequently asked questions
- What are planetary hours and how do I use them?
- A planetary hour is one of the 24 unequal 'temporal hours' into which the classical day is divided — twelve from sunrise to sunset and twelve from sunset to sunrise — each ruled by one of the seven planets in the Chaldean order. Traditionally you begin a task in the hour of the planet governing its theme, ideally on the day ruled by a friendly planet. It is a way of deliberately choosing a start-time, not a guarantee of outcome.
- Are planetary hours based on 60-minute hours?
- No. They are one-twelfth of the actual daylight (or night), so their length changes daily with the season and your latitude — shorter than 60 minutes in winter days, longer in summer. That is why a planetary-hour table always has to be computed for a specific date and location; a fixed clock-hour approximation will drift off the real boundaries.
- Why does my day start at sunrise and not midnight?
- Because the classical planetary-day convention runs from sunrise to sunrise, matching the older astronomical day. The first hour at sunrise takes the day's own ruler, and every later hour is the next step of the Chaldean sequence. This is what makes the hours and the weekday names line up. A minority of sources number from midnight instead, so always check a table's stated convention.
- What is the Chaldean order?
- It is the sequence Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon — the traditional descending 'speed' of the planets as seen from Earth. Running it around a clock starting at each sunrise gives the day's ruler at hour one and produces the familiar weekday sequence (Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn) as a by-product. It is the arithmetic the whole system rests on.
- Is my data private?
- Calculations run entirely in your browser. Your birth data is never uploaded, never stored on a server, and never shared. The sunrise, sunset and hour table are computed locally from the date and place you enter; nothing is uploaded or stored.
Written by
Elena Marchetti
Founder & Staff Astrologer
Methodology reviewed by
Dr. Amara Osei
Astronomy Reviewer
Published 2026-10-01 · Updated 2026-10-01 · Calculated with sub-arcsecond astronomy (VSOP87/ELP via astronomy-engine)