Question

In the computational process of finding mean planetary positions (Madhyamagraha-anayana), which specific day-count or 'Dyugana' must be calculated first?

• A. Chandra (Lunar Day count)
• B. Savana (Terrestrial/Civil Day count)
• C. Saura (Solar Day count)
• D. Divya (Divine Day count)

Hint:

"Ahar" = Day, "Gana" = Count. Planets move every day on Earth. Therefore, we use the "Savana" (Earth/Civil) day to count their movement. Ahargana is ALWAYS a count of Savana days.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In Indian mathematical astronomy (Siddhanta), the calculation of a planet's position for any given moment begins with finding the total number of days that have passed since a fixed starting point (Epoch), usually the beginning of the Kali Yuga. This cumulative sum of elapsed days is called Ahargana or Dyugana.

Step 2: Mathematical Rationale:
Mean planetary positions are based on the average daily motion (Madhyama Gati). For this calculation to be mathematically valid, we need a constant and uniform unit of time.
- Lunar Days (Tithis) are not uniform; they vary in duration based on the relative speeds of the Sun and Moon.
- Solar Days (Saura) are based on the Sun's movement of one degree, which also varies slightly throughout the year.
- Savana Day is defined as the period from one terrestrial sunrise to the next. It is the civil day we experience. Because it is a fixed unit relative to the Earth's rotation, the planetary motions are tabulated based on Savana days.

Step 3: The Calculation Process:
To find the Ahargana:
1. Total Saura years are converted to Saura months.
2. Elapsed lunar months are added.
3. Intercalary months (Adhika Maasas) are added to find total lunar months.
4. Total lunar months are converted to lunar days (Tithis).
5. Omitted days (Kshaya Tithis) are subtracted to finally arrive at the Savana Dyugana.
\[ \text{Mean Planet Position} = (\text{Daily Motion} \times \text{Savana Ahargana}) \pmod{360^\circ} \]

Step 4: Final Answer:
Therefore, for the calculation of mean planets, the Savana day-count (Ahargana) is the required mathematical input.