Three Phases of Indian Astronomy
┌───────────────────────────────────────────────────┐
│ INDIAN ASTRONOMY — EVOLUTION │
├──────────────────┬────────────────────────────────┤
│ PRE-SIDDHANTIC │ Vedic period (~1500–500 BCE) │
│ │ Vedanga Jyotisha (~1400 BCE) │
├──────────────────┼────────────────────────────────┤
│ SIDDHANTIC │ Aryabhatiya (499 CE) │
│ │ Brahmasphuta-siddhanta (628) │
│ │ Surya-siddhanta (~7th CE) │
├──────────────────┼────────────────────────────────┤
│ POST-SIDDHANTIC │ Bhaskara II's Siddhanta- │
│ │ Shiromani (1150 CE) │
│ │ Kerala School (14th–17th CE) │
│ │ Sawai Jai Singh's Jantar │
│ │ Mantar observatories (18th) │
└──────────────────┴────────────────────────────────┘Pre-Siddhantic Period
Vedanga Jyotisha (attributed to Lagadha, ~1400 BCE) is the oldest surviving Indian astronomical text. Its purpose was practical: to determine muhurta (auspicious time) for Vedic rituals.
Key features:
- 5-year yuga cycle (1830 days) to harmonise lunar and solar calendars
- Tracking of 27 nakshatras (lunar constellations)
- 12 lunar months, intercalation rules
- Definition of tithi, paksha, maasa, ritu, ayana
Siddhantic Period — The Classical Age
The word Siddhanta means "established conclusion." During this era, astronomy became a mathematically rigorous, theory-based science.
Aryabhata (476–550 CE), Aryabhatiya:
- Sphericity and rotation of Earth.
- Heliocentric implications (Earth rotates, stars are stationary).
- Calculated length of year = 365.358 days (modern: 365.256).
- Eclipses explained by shadow of Earth/Moon (not by Rahu/Ketu mythology).
- Estimated diameters of Sun, Moon, and Earth's circumference within 1% accuracy.
Brahmagupta (598–668 CE), Brahmasphuta-siddhanta:
- Rules of arithmetic including zero and negative numbers.
- Gravity — "All heavy things are drawn to Earth, as it is in their nature."
- Methods to predict eclipses, planetary positions.
Bhaskara II (1114-1185 CE), Siddhanta-Shiromani:
- Most refined Siddhantic text.
- Anticipated calculus concepts: "Instantaneous velocity" (tatkalika gati).
- Stated that gravity is a force.
Key Concepts of Siddhantic Astronomy
Sun ☉───────● ●───●───●───●───●───●───●
1 2 3 4 5 6 7
Mer Ven Earth Mars Jupiter Saturn
GRAHA (planet) ORDER in
Siddhantic systemYuga System:
| Yuga | Years |
|---|---|
| Satya | 1,728,000 |
| Treta | 1,296,000 |
| Dvapara | 864,000 |
| Kali | 432,000 |
| Total Mahayuga | 4,320,000 |
A Kalpa = 1,000 Mahayugas = 4.32 billion years. Strikingly close to modern estimates of the age of the Sun (4.6 billion years).
Post-Siddhantic Period
- Kerala School (Madhava, Nilakantha) — refined planetary models. Nilakantha (1500 CE) proposed a partially heliocentric model — Mercury and Venus orbit the Sun, which orbits the Earth — anticipating Tycho Brahe by 80 years.
- Sawai Jai Singh II (1688–1743) — built five massive observatories (Jantar Mantar) at Jaipur, Delhi, Ujjain, Mathura, Varanasi. Their instruments (e.g., the Samrat Yantra — world's largest sundial, 27 m tall) measure time to 2-second accuracy.
Samrat Yantra (Jaipur)
╱│
╱ │ Gnomon angle =
╱ │ Latitude of Jaipur
╱ │ (~27°)
╱ │
╱──────────┤
│ Marble quadrants
│ graduated in minutes
│ and secondsLasting Influence
- The Indian calendar (Saka era) is still official in India alongside the Gregorian.
- Concepts of rotation, gravity, and place-value arithmetic travelled west through Islamic astronomers.
- Modern planetariums in India (Birla, Nehru) explicitly trace their lineage to Aryabhata.