Knowledge Traditions And Practices Of India: Class 11 — Chapter 5: Astronomy in India

Introduction to Indian Astronomy

Astronomy, the study of celestial objects, is one of India's oldest sciences, deeply rooted in the Vedic period and practical daily needs.

Vedic Speculations: Early cosmological questions regarding the origin of the universe couched in philosophical terms.
Practical Needs: Agriculture (predicting rains, sowing crops), social/religious events (marriages, festivals), and omen tracking (eclipses, comets).
Core Preoccupations: Devising calendars, predicting eclipses, tracking planetary motions, and estimating celestial distances.

Astronomical Practices & the Indian Calendar

The traditional Indian calendar is a sophisticated luni-solar system designed to harmonize lunar phases with the solar year.

Sidereal Period: The orbital period of the moon with respect to the stars, lasting $27.3$ days.
Synodic Period: The orbital period observed from Earth relative to the Sun, lasting $29.5$ days.
Lunar Month Halves: Divided into Kᤳᥣᥑapakᥣa (dark half, starting after full moon) and Œuklapakᥣa (bright half, starting after new moon). Each half begins with day one, called ekam.
Nakᥣatras: 27 or 28 prominent stars associated with each day of the moon's orbit to define its position.
RāŒi Cakra: The Zodiac belt, spanning $8^\circ$ on either side of the ecliptic, divided into 12 constellations (RāŒis).

The calendar reconciles the $354$-day lunar year with the $365.25$-day solar year.

Sa᥅krānti: The day the Sun enters a new RāŒi (e.g., Makarā Sa᥅krānti).
Month Names: Named after the Nakᥣatra visible on the full moon day of that month (e.g., Caitra from Citrā).
Adhikamāsa: An extra intercalary month (also called malamāsa) added approximately every $2.7$ years to prevent seasonal drift.
Tithi: A lunar date defined by a $12^\circ$ angular separation between the Sun and Moon. Its duration varies from $19$ to $26$ hours due to elliptic orbits.

Scientific Explanation of Eclipses

Ancient Indian astronomers provided physical, geometric explanations for eclipses, debunking mythological terrors.

Solar Eclipse: Occurs when the Moon passes directly between the Earth and the Sun, blocking solar light.
Lunar Eclipse: Occurs when the Earth passes between the Sun and the Moon, casting its shadow on the Moon.
Line of Nodes: The intersection line of the inclined orbital planes of the Earth and Moon. The endpoints are called nodes, historically named Rahu and Ketu. Eclipses only occur when the Moon is at one of these nodes.
Mythological Metaphor: The popular myth of demons Rahu and Ketu devouring the Sun arose from a misunderstanding of these physical nodal points.

Solstices: Uttarāyaᥑa and Dakᥣiᥑāyana

Astronomers tracked the annual shifting of the sunrise position and day length.

Uttarāyaᥑa: The northward journey of the Sun starting from the winter solstice, associated with summer's approach and considered highly auspicious.
Dakᥣiᥑāyana: The southward journey of the Sun starting from the summer solstice, indicating approaching winter.
Precession: Due to the slow shift in Earth's rotational axis, the date of Uttarāyaᥑa has shifted over 2000 years from January 14 to around December 23.
Cultural Reference: In the Mahābhārata, Bhĩᥣma chose to delay his death until the onset of the auspicious Uttarāyaᥑa.

Prominent Ancient Indian Astronomers

India produced several pioneering astronomers and mathematicians whose works laid the foundation for global mathematical sciences.

Astronomer	Era / Date	Major Works	Key Contributions
Āryabhaᥣᥣa	b. 476 CE	Āryabhaᥣĩyam	Proposed spherical Earth rotating on its axis; calculated $\pi \approx 3.1416$; introduced large time units and circular units of arc; suggested adding adhikamāsa.
Varāhamihira	6th Century CE	Pacasiddhāntikā, Bᤳhatsa᥅hitā	Compiled five historical astronomical systems; calculated the precession of equinoxes as $50.32$ seconds of arc per year.
Bhāskara I	b. 600 CE	Mahābhāskarĩya, Laghubhāskarĩya	Established the positional value system using a circle for zero; commented extensively on Āryabhaᥣĩyam.
Brahmagupta	7th Century CE	Brahmaguptasiddhānta	First to treat zero as a number; formulated rules for positive/negative numbers; solved quadratic equations; established $\sqrt{10} \approx 3.162277$ as an approximation for $\pi$.
Bhāskara II (Bhāskarācārya)	b. 1114 CE	SiddhāntaŒiromaᥑi, Karaᥑakutšhala, Lĩlāvatĩ, Bĩjagaᥑita	Introduced division by zero as infinity ($3/0 = \infty$); used algebraic letters for unknowns; solved the Pell Equation ($x^2 = 1 + py^2$).

Flourishing between the 14th and 16th centuries CE, this school made revolutionary breakthroughs in calculus and planetary models.

ParameŒvara (1362–1455): Proposed an early heliocentric model of the solar system.
Nĩlakaᥑᥣha (c. 1500 CE): Further developed the heliocentric model, decades before Copernicus.
Jyeᥣᥣhadeva: Provided the first systematic proofs for the infinite power series of sine, cosine, and arctangent functions, predating European calculus by a century.

Later Developments & Modern Astronomy in India

India's astronomical legacy transitioned from massive stone observatories to state-of-the-art modern research facilities.

Jantar Mantar: Massive stone observatories built between 1723 and 1735 by Maharaja Sawai Jai Singh II at Delhi, Jaipur, Ujjain, Mathura, and Varanasi, featuring highly accurate sundials and planetary tracking instruments.

Ooty Radio Telescope (ORT): Conducts key research on radio galaxies, quasars, and pulsars.
Giant Metrewave Radio Telescope (GMRT): Located near Pune; consists of 30 steerable parabolic dishes; discovered the massive Saraswati supercluster of galaxies.
Chandrayaan-1: India's lunar mission that confirmed the presence of water on the Moon.
Indian Astronomical Observatory (IAO): Located at Hanle, Ladakh (4517 m altitude); operates the remotely controlled Himalayan Chandra Telescope (HCT).
Devasthal Optical Telescope (DOT): Located at Nainital (ARIES); at 3.6 meters, it is India's largest optical telescope.
Global Collaborations: India is a key partner in major international projects including the Thirty Meter Telescope (TMT), LIGO-India, and the Square Kilometer Array (SKA).