Step 1: Understanding the Concept:
The 'Navāṃśa' is the most important divisional chart (Varga) in Vedic Astrology, where each zodiac sign of $30^{\circ}$ is divided into nine equal parts of $3^{\circ}20'$ each. The calculation of which sign a planet occupies in the Navāṃśa depends on the element (Tattva) of the sign it occupies in the main birth chart (Rāśi). The starting point for counting the nine divisions varies according to whether the sign is Fire, Earth, Air, or Water.
Step 2: Detailed Explanation:
The traditional rule for Navāṃśa calculation follows the 'Tattva' or elemental grouping of the 12 signs:
1. Fire Signs (Agni Tattva): These are Aries (1), Leo (5), and Sagittarius (9). For any planet in these signs, the Navāṃśa counting always begins from Aries (Mēṣa).
2. Earth Signs (Pṛthvī Tattva): These are Taurus (2), Virgo (6), and Capricorn (10). For any planet in these signs, the Navāṃśa counting always begins from Capricorn (Makara).
3. Air Signs (Vāyu Tattva): These are Gemini (3), Libra (7), and Aquarius (11). For any planet in these signs, the Navāṃśa counting always begins from Libra (Tulā).
4. Water Signs (Jala Tattva): These are Cancer (4), Scorpio (8), and Pisces (12). For any planet in these signs, the Navāṃśa counting always begins from Cancer (Karka).
The question asks us to arrange the starting points in the order of the elements (Fire \(\rightarrow\) Earth \(\rightarrow\) Air \(\rightarrow\) Water).
- Fire corresponds to B (Mēṣa).
- Earth corresponds to D (Makara).
- Air corresponds to A (Tulā).
- Water corresponds to C (Karka).
Therefore, the correct sequence of labels is B, D, A, C. This systematic division ensures that the Navāṃśa chart covers the entire zodiac and maintains a mathematical harmony with the Nakṣatra Padas. Each Nakṣatra has 4 Padas, and since there are 2.25 Nakṣatras per sign, there are exactly 9 Padas (9 Navāṃśas) in every zodiac sign. This creates a bridge between the stellar (Nakṣatra) and solar (Rāśi) systems of measurement.
Step 3: Final Answer:
The correct sequence of the starting points for Navāṃśa calculation is B, D, A, C.