Question

The Sun's declination (Krānti) is said to be zero when the Sun is moving exactly along which celestial circle?

• A. Celestial Equator (Nāḍī-vr̥ttē)
• B. Meridian (Yāmyōttara-vr̥ttē)
• C. Horizon (Kṣitija-vr̥ttē)
• D. Prime Vertical (Mahad-vr̥ttē)

Hint:

'Krānti' is distance from the 'Equator'. Therefore, if distance is zero, the Sun must be *on* the Equator. Sanskrit for Equator = Nāḍī-vr̥tta.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
'Krānti' (Declination) is the angular distance of a celestial body north or south of the Celestial Equator. It is analogous to latitude on Earth. The Sun moves along the 'Krānti-vr̥tta' (Ecliptic), which is tilted at an angle of \( 24^\circ \) (in ancient Siddhanta) relative to the Celestial Equator.

Step 2: Detailed Explanation:
1. Nāḍī-vr̥tta: In Sanskrit astronomy, the Celestial Equator is called the Nāḍī-vr̥tta. It is the projection of the Earth's equator into space. By definition, the declination of any point on the Nāḍī-vr̥tta is zero.
2. The Phenomenon: Twice a year, during the Spring Equinox (Vēṣa Saṃpāta) and the Autumnal Equinox (Tulā Saṃpāta), the path of the Sun (Ecliptic) intersects the Celestial Equator (Nāḍī-vr̥tta). At these two precise moments, the Sun has no angular distance from the equator. Hence, its Krānti is zero.
3. Why other options are incorrect:
- Kṣitija-vr̥tta (Horizon): A Sun on the horizon has an altitude of zero, but its declination depends on the time of year.
- Yāmyōttara-vr̥tta (Meridian): This is a north-south circle. The Sun crosses it every day at noon, but its declination is only zero on equinoxes.
- Mahad-vr̥tta: This usually refers to the Prime Vertical (east-west circle passing through Zenith). While important for Gnomon calculations, it doesn't define the zero-point of declination.

When Krānti is zero, the Sun rises exactly in the East and sets exactly in the West. Day and night are equal in length (12 hours/30 Ghaṭis each) everywhere on Earth. This state represents the balance of cosmic forces and is the starting point for calculating the Sun's 'Cara' (ascensional difference).

Step 3: Final Answer:
The declination is zero when the Sun is on the Nāḍī-vr̥tta (Celestial Equator).