The biodynamic calendar gives every hour a type, fruit, flower, leaf or root, depending on which constellation the Moon is passing in front of. Here's how that works, and how Moonvine calculates it.
The Moon's monthly trip around the zodiac
Seen from Earth, the Moon moves against the background stars by about 13° a day and completes a full circuit in about 27.3 days (the sidereal month). Along the way it passes in front of the twelve constellations of the zodiac, spending roughly two to three days in each.
Four elements, four day types
Biodynamics follows the old idea that the zodiac constellations come in four groups of three, each tied to a classical element. Maria Thun's sowing trials linked each element to one part of the plant, and through it to a day type:
| Element | Constellations | Day type | For wine |
|---|---|---|---|
| Fire | Aries, Leo, Sagittarius | Fruit | Best for wine |
| Air | Gemini, Libra, Aquarius | Flower | Good for wine |
| Water | Cancer, Scorpio, Pisces | Leaf | Not ideal |
| Earth | Taurus, Virgo, Capricorn | Root | Poor for wine |
Because the elements alternate around the zodiac, the day type changes every two to three days and each type comes back about every nine days.
Real constellations, not zodiac signs
This is the detail most calendars get wrong. Astrology uses twelve equal 30° signs fixed to the spring equinox. Over two thousand years the equinox has drifted, through the precession of Earth's axis, by about 24°, so the signs no longer line up with the stars they were named after. The constellations themselves are also unequal: Virgo spans about 44° of the ecliptic, Cancer barely 20°.
Maria Thun's calendar uses the actual constellations as astronomers define them, with the small slice of Ophiuchus counted as part of Scorpio. Moonvine does the same, using the official IAU constellation boundaries. A calendar based on signs can be wrong by a day or more.
Unfavorable windows: nodes and perigee
The Moon's orbit is tilted about 5° to the Sun's path. Twice each month it crosses that path, at points called the lunar nodes. Once a month it also swings closest to Earth, at perigee. Biodynamic calendars treat the hours around these events as unfavorable: growers don't sow or harvest, and tasters skip serious bottles.
Moonvine marks six hours either side of each node crossing and perigee as unfavorable. Those windows interrupt whatever day type would otherwise be running.
Ascending and descending moon
Separate from waxing and waning, the Moon's daily arc across the sky climbs higher for about two weeks, then sinks lower for two weeks. Biodynamic growers call these the ascending and descending moon. An ascending moon is linked with sap rising, which makes it good for grafting and harvesting fruit. A descending moon draws energy down, which suits planting and soil work. Moonvine shows which one is underway, but it doesn't change the day type.
How Moonvine calculates it
- On your phone, no server. The Moon's position comes from Jean Meeus's lunar theory (Astronomical Algorithms), accurate to about 0.01°. At 0.55° per hour, that puts each change within a few minutes.
- Fixed to the stars. The Moon's position is corrected for precession so it can be compared with the constellation boundaries.
- Checked against the references. The results were tested against Meeus's worked example and a published biodynamic calendar.
- Your time zone. Every time is shown in your local time, including on this website.
Want to see it in action? The today page runs the same calculation live in your browser.
Questions
Why does my printed calendar show different times?
Printed calendars are usually set for one time zone, often Central European Time, so times shift for everyone else. Some also round to the nearest hour. Moonvine calculates exact times for your own time zone.
Is the biodynamic calendar the same as astrology?
No. It uses the same constellation names, but it tracks where the Moon actually is against the stars, using unequal constellations rather than the equal 30° signs of astrology.
Who was Maria Thun?
Maria Thun (1922–2012) was a German biodynamic researcher. Her decades of sowing trials produced the fruit, flower, leaf and root calendar that her family still publishes every year.
