Why Planetary Hours Are Not 60 Minutes: Latitude & Season Table

A planetary hour is one-twelfth of the actual daylight from local sunrise to sunset (or one-twelfth of the night from sunset to the next sunrise). It equals 60 clock minutes only when daytime and nighttime are exactly 12 hours each. Away from the equator, summer day hours expand and winter day hours shrink—reaching 105.71 minutes per day hour and 14.31 minutes per night hour in Reykjavik on the June solstice.

Calculate today’s 24 planetary hours for your city in the planetary hours calculator.

Day and night planetary hour durations across four latitudes (2026)

We computed local sunrise, sunset and the following sunrise on the March equinox (March 20, 2026), June solstice (June 21, 2026) and December solstice (December 21, 2026) for Singapore (1.29° N), New York (40.71° N), London (51.51° N) and Reykjavik (64.15° N).

Why equinox planetary hours are still not exactly 60.00 minutes

Even on March 20, the table shows day hours slightly longer than 60 minutes (60.54 minutes in Singapore to 61.23 minutes in Reykjavik) and night hours slightly shorter. Two physical definitions explain why daylight exceeds 12 hours on the equinox:

1. Atmospheric refraction: Earth’s atmosphere bends sunlight upward by about 34 arcminutes at the horizon, making the Sun visible before its geometric center reaches the horizon and after it sinks below.
2. Solar disc radius: Standard almanacs and our calculator define sunrise and sunset by the upper limb of the Sun’s disc (radius about 16 arcminutes) rather than its center. Together, refraction and semi-diameter place the Sun’s center about 50 arcminutes below the geometric horizon at sunrise and sunset.

Notice that this differs from the astrological Ascendant, which uses the geometric center of the ecliptic on an unrefracted horizon; see our sunrise versus Ascendant comparison.

How Chaldean rulers and polar boundaries work

Each day starts at local sunrise with the planet ruling that weekday (Sun on Sunday, Moon on Monday, Mars on Tuesday, Mercury on Wednesday, Jupiter on Thursday, Venus on Friday, Saturn on Saturday) and cycles through the Chaldean order (Saturn → Jupiter → Mars → Sun → Venus → Mercury → Moon) across the 12 day hours and 12 night hours. Because 24 divided by 7 leaves a remainder of 3, the first hour of the next sunrise advances three steps in the Chaldean sequence, producing the traditional weekday order.

Above the polar circles, when the Sun remains continuously above or below the horizon for a full local day, no sunrise-to-sunset division exists and our calculator reports that planetary hours are undefined for that date.

Method and limits

Sunrise and sunset instants come from Astronomy Engine SearchRiseSet at sea-level elevation for each city’s coordinates. Durations are exact elapsed minutes divided by 12. Traditional hour elections are historical symbolic practices, not tested predictors of task success.

Download the research and comparison JSON · Reproduce these tables (TypeScript source). Output is licensed under CC BY 4.0; credit Natal Chart Lab and link to this article.

Prepared with AI assistance and checked against calculation code and saved data. Astronomical calculations and dataset statistics do not establish astrological claims about personality, relationships or future events.