Why does Aplune use two coordinate systems for signs and lunar mansions?
The references, degrees, and period-start relationships of tropical zodiac signs and Dhruva lunar mansions.
In this article
Signs begin at the vernal equinox
Aplune uses the tropical zodiac for Rāśi: the vernal equinox marks zero degrees Aries, and the circle is divided into twelve 30° sections. A planet’s tropical longitude determines its sign and is also used in divisional chart calculations. Counting twelve whole-sign houses from the Ascendant’s sign establishes each planet’s house lordships.
This division begins from seasonal reference points. The Lahiri sidereal zodiac uses a different stellar reference, so the same birth details may show different sign names under the two settings.
Lunar mansions use Dhruva equatorial positions
This site’s twenty-seven lunar mansions use the Dhruva Equatorial method. The program reads planetary right ascension, establishes a reference from the right ascension of the Galactic Center, Sgr A*, and aligns it with the midpoint of Mula at 246°40′. The normalized full circle is then divided into 27 sections of 13°20′ each.
Dhruva uses right ascension to establish lunar mansion positions. The ecliptic and equator are different planes, and conversion involves planetary ecliptic latitude, time and the reference method used. Its degrees therefore differ from those obtained by subtracting precession from tropical longitude. Different lunar mansion coordinates can also yield different positions within a mansion.
Why lunar mansions affect major-period dates
Vimshottari uses the natal Moon's lunar mansion to determine the starting planetary ruler, and the proportion of the mansion remaining for the Moon to traverse to determine the balance of the first major period. If two calculation methods place the Moon at different positions within the mansion, the starting date changes; near a boundary, the starting ruler may also change.
For example, if the Moon is exactly halfway through a mansion ruled by Venus, half of its 20-year major period remains: 10 cycle years. This site converts dates using a Saura year of 365.2422 days. The mansion, the proportion within it and the year length must each match; changing only one may not align two timelines.
How to use the lunar mansion table in the knowledge library
The 0°–360° ranges in the lunar mansion entries use normalized Dhruva equatorial positions. Each mansion has four Padas of 3°20′ each; use the corresponding Dhruva degree when consulting the table. Tropical longitude is used for this site's sign and divisional chart calculations.
When comparing chart calculations, record tropical longitude, lunar mansion coordinate conventions and the year length used for dasha commencement. Identify the first field that diverges, then compare the Ascendant, divisional charts and dates. This reduces fruitless repeated changes to birth details.
References
- Ernst Wilhelm's zodiac and lunar mansion framework; this site's Calc implementation of Dhruva equatorial positions, starting Vimshottari dasha and Saura year length.
- Zodiac and lunar mansion conventions used on this site
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