A D30 chart can look surprisingly different from D1. This guide separates the attested five-band rule, the derived sign mapping, and input limitations.
Why the sign parity matters
The odd rāśis are Aries, Gemini, Leo, Libra, Sagittarius, and Aquarius. The even rāśis are Taurus, Cancer, Virgo, Scorpio, Capricorn, and Pisces. In any odd sign, the first five degrees belong to Mars; in any even sign the first five belong to Venus. The underlying D1 sign changes the parity, but the five possible D30 signs are otherwise the same for every sign of the same parity.
Parāśara 6.27 states the unequal lordship sequence and reversal. Varāhamihira’s Bṛhat Jātaka 1.7 corroborates the widths and order. The named D30 signs in this tool follow Rao’s §6.2.17 chart table, which selects one of each ruler’s two signs according to odd or even natal rāśi. The texts’ ruler rule and the manual’s sign assignment are related but should not be collapsed into a claim that one verse spells out every assigned sign.
Complete sign assignment table
Each range includes its start and excludes its end. At 5° exactly, use the second row; at 30° exactly, enter the next D1 rāśi and begin its first row. The table gives the sign, not a within-sign D30 degree.
| Band | Odd degree | Odd ruler | D30 sign | Even degree | Even ruler | D30 sign |
|---|---|---|---|---|---|---|
| 1 | 0°–5° | Mars | Aries | 0°–5° | Venus | Taurus |
| 2 | 5°–10° | Saturn | Aquarius | 5°–12° | Mercury | Virgo |
| 3 | 10°–18° | Jupiter | Sagittarius | 12°–20° | Jupiter | Pisces |
| 4 | 18°–25° | Mercury | Gemini | 20°–25° | Saturn | Capricorn |
| 5 | 25°–30° | Venus | Libra | 25°–30° | Mars | Scorpio |
Work through two placements
For 14° Aries, Aries is odd and 14° lies inside 10°–18°. Jupiter rules that band, and the mapped D30 sign is Sagittarius. For 14° Taurus, Taurus is even and 14° lies inside 12°–20°. Jupiter again rules the band, but the D30 sign is Pisces. At exactly 18° Aries the Mercury band begins; one arcsecond before remains Jupiter’s band. At exactly 12° Taurus the Jupiter band begins; one arcsecond before remains Mercury’s band.
Normalize a sidereal longitude to 0° through just below 360°; divide by 30° to find the D1 sign and degree within that sign. Choose the odd or even column above. No fractional D30 degree is presented because the cited five-band assignment by itself does not define a unique coordinate within its resulting sign.
Conventions and data limits
Some modern D30 descriptions use an equal 1° mapping rather than this five-band Triṃśāṃśa. Some software also assigns a continuous derived degree inside a five-band sign. Those are additional conventions, so check the method before comparing results. This tool deliberately reports the classical band and sign only.
The D1 inputs use Astronomy Engine 2.1.19 with an approximate Lahiri ayanamsha. They do not use Swiss Ephemeris. A recorded time, birthplace coordinates, and historical UTC offset are needed for the D30 ascendant. Local dates from 1800 to 2100 are accepted. The calculator cannot reconstruct a birthplace’s historical time zone. It warns when a displayed point lies within 0.05° of a band boundary; a different time, ayanamsha, lunar-node convention, or ephemeris can change close placements.
References
- Bṛhat Parāśara Horā Śāstra 6.27 — Sanskrit, translation, and the five odd-sign widths with reversal in even signs.
- Bṛhat Jātaka 1.7 — an independent classical statement of the same unequal widths.
- P. V. R. Narasimha Rao, Vedic Astrology: An Integrated Approach, §6.2.17 (PDF p. 58) — explicit odd and even D30 sign mapping.
- SIA Vigyan D30 description — example of a competing equal-degree description under the D30 label.
- Astronomy Engine 2.1.19 — astronomy library for the underlying D1 coordinates.