Lunar month
The time the Moon takes for one orbit. Depending on the point of reference it lasts 27.2 to 29.5 days, and each of these months carries its own rhythm in the biodynamic calendar.
Why there are several lunar months
A lunar month is one orbit of the Moon around the Earth. How long it lasts depends on the point of reference: the background of stars, the Sun, the vernal point, the lunar node or perigee. Each of these points of reference moves a little itself, and so the lengths come out differently.
In the biodynamic calendar these rhythms run at the same time. Each one carries its own mark: the day type, the rise and fall, the phase of light, the node and perigee.
The lunar months at a glance
| Month | Mean length | Measured | Rhythm in the calendar |
|---|---|---|---|
| sidereal | 27.32 days (27 d 7 h 43 min) | from star to star | orbit through the constellations, the day types |
| tropical | 27.32 days (27 d 7 h 43 min) | from vernal point to vernal point | Moon’s course, ascending and descending |
| synodic | 29.53 days (29 d 12 h 44 min) | from New Moon to New Moon | Moon phases |
| draconic | 27.21 days (27 d 5 h 6 min) | from node to node | lunar nodes and eclipses |
| anomalistic | 27.55 days (27 d 13 h 19 min) | from perigee to perigee | perigee and apogee |
The values are means. Individual orbits differ from them: a synodic month lasts between about 29.27 and 29.83 days.
What follows for the calendar
Because the months differ in length, the rhythms shift against one another. A root day falls one time in the waxing Moon, another time in the waning Moon. Each month the Full Moon stands about 29 degrees further east, mostly in front of the next constellation.
The synodic month is a good two days longer than the sidereal month. In the time of one orbit the Earth moves a little further round the Sun, and the Moon has to make up this angle before it stands between Earth and Sun again.
The interplay of the draconic and the synodic month gives the saros cycle. After 223 synodic months, 18 years and a good 11 days, New Moon, Full Moon and node stand almost the same again, and the eclipses repeat.
Sources
- Month, Wikipedia
- Lunar month, Lunar node, Orbit of the Moon, Wikipedia
- Saros (astronomy), Wikipedia
Frequently asked questions about the lunar month
How long is a lunar month?
From New Moon to New Moon 29.53 days on average. For one orbit through the constellations the Moon needs 27.32 days.
What is the difference between the sidereal and the synodic month?
The sidereal month measures the orbit against the stars, 27.32 days. The synodic month measures the way from New Moon to New Moon, 29.53 days.
Which lunar month does the planting calendar use?
All of them at once. The day type follows the sidereal month, the rise and fall the tropical month, the phase the synodic month, the nodes the draconic month and perigee the anomalistic month.