Indian Astronomy

Previously, our look at ancient astronomy has focused heavily on Mesopotamia, European astronomy and the Islamic Golden Age. But, it is impossible to ignore the role of the great Indian astronomers in any study of astronomy; their contribution to science inspired Hellenic, Islamic and European thought for centuries, with their work brought the great Silk Road into Europe.

Indian astronomy was strongly tied to their religious and spiritual world outlook, but it included other valid incredible findings. It acted as a stimulus for the subcontinent's development in mathematics, one of India's biggest legacies passed on to the western world.

The first accounts of advanced astronomy in India date back to at least 2000 BCE, where they are included in the Rigveda (c1700-1100 BCE), one of Hinduism's most significant and main texts.The ancient Indian astronomy used the stars and the planets to construct astrological charts and interpret omens, build complex mathematical models and establish other interesting theories, many of which went through the Islamic world and through Europe.

The Rigveda showed the Indians split the year into 360 days, and the year was subdivided into thirty-day 12 months. In order to bring the calendar back in line with the solar year, two intercalary cycles were introduced every 5 years, implying that years lasted 366 days.The Indian year, though, often rotated four days in every five years and over the centuries, Indian astronomers were continually changing and modifying their calendars. The text further shows that the Indians used four cardinal points to insure the altars were guided correctly.

The Jyotisa Vedanga, the first Vedic text to mention astronomical data, records events going back as far as 4000 BCE, although many archaeoastronomers believe that this text may include observations from as early as 11 000 BCE. They point out that some of the records may have been copied from earlier manuscripts, but this is an area where more research is needed, as many of the references are unclear and couched in religious terminology.

This period saw many advances in measuring time and the procession of the heavens, with a few proto-theories about the structure of the universe. More importantly, this period saw the transmission of ideas between the Indians, Babylonians, Greeks, and Persians. This exchange of theories and philosophy was extremely important to the development of astronomy.

Indian Astronomy and the Siddhantic Era

In this period, a new branch of astronomy, diverging from the Vedas began. Called the Siddhantic Era, it began with a series of books called the Siddhanat, ‘Solutions,’ which charted the solar year, including solstices, equinoxes, lunar periods, solar and lunar eclipses, and planetary movements. The Siddhantic Era saw three great Indian astronomers, sadly little known in the west, despite the great advances that they made.

By the first century CE, Indian astronomers proposed that the stars were exactly like the sun, but much further away, at a time when the Greeks were still using celestial crystal spheres to explain the cosmos. They also understood that the earth was spherical, and Indian astronomers attempted to calculate the circumference of the planet.

It is difficult to pick out exactly the thoughts of the Indians, because many of their observations and ideas are revealed in religious verses, which are always open to interpretation. Yajnavalkya (c 3rd Millennium BCE) believed in a heliocentric universe, although some verses from as early as 3000 BCE allude to this; however, these early references are vague and we must be careful to apply the same strict definitions that we do to megalithic astronomy and avoid confirmation bias. In his text, called the ‘Shatapatha Brahmana,’ he also measured the distance of the sun from the earth, and the distance of the moon from the earth, to be 108 times the diameter of these bodies, very close to the modern measurements of 107.5 for the sun and 110.6 from the moon. The early Siddhantic Era is poorly recorded and gives only a tantalizing glimpse into the mind of the ancient Indian astronomers and mathematicians.

Astronomers

Lagadha

1st  BCE

The earliest astronomical text—named Vedānga Jyotisya details several astronomical attributes generally applied for timing social and religious events.

The Vedānga Jyotisya also details astronomical calculations, calendrical studies, and establishes rules for empirical observation.

Aryabhata

476–550 CE

Aryabhata was the author of the Āryabhatīya and the Aryabhatasiddhanta, had a profound influence on the development of Islamic astronomy. Its contents are preserved to some extent in the works of Varahamihira, Bhaskara I, Brahmagupta, and others.

It is one of the earliest astronomical works to assign the start of each day to midnight.

Aryabhata explicitly mentioned that the earth rotates about its axis, thereby causing what appears to be an apparent westward motion of the stars.

Aryabhata also mentioned that reflected sunlight is the cause behind the shining of the moon.

Brahmagupta

598–668 CE

Brahmasphuta-siddhanta(Correctly Established Doctrine of Brahma, 628 CE) dealt with both Indian mathematics and astronomy.

Brahmagupta calculated the instantaneous motion of a planet, gave correct equations for parallax, and some information related to the computation of eclipses.

His works introduced Indian concept of mathematics based astronomy into the Arab world.

He also theorized that all bodies with mass are attracted to the earth.

Varāhamihira

505 CE

Varāhamihira was an astronomer and mathematician who studied and Indian astronomy as well as the many principles of Greek, Egyptian, and Roman astronomical sciences. His Pañcasiddhāntikā is a treatise and compendium drawing from several knowledge systems.

Bhāskara I

629 CE

Authored the astronomical works

Mahabhaskariya(Great Book of Bhaskara),

Laghubhaskariya(Small Book of Bhaskara), and

Aryabhatiyabhashya(a commentary on the Āryabhatīya written by Aryabhata).

Planetary longitudes, heliacal rising and setting of the planets, conjunctions among the planets and stars, solar and lunar eclipses, and the phases of the Moon are among the topics Bhaskara discusses in his astronomical treatises.

Lalla

8th CE

Author of the Śisyadhīvrddhida(Treatise Which Expands the Intellect of Students), which corrects several assumptions of Āryabhata.

The Śisyadhīvrddhida of Lalla itself is divided into  two parts: Grahādhyāya and Golādhyāya.

Grahādhyāya (Chapter I-XIII) deals with planetary calculations, determination of the mean and true planets, three problems pertaining to diurnal motion of Earth, eclipses, rising and setting of the planets, the various cusps of the moon, planetary and astral conjunctions, and complementary situations of the sun and the moon.

Golādhyāya (chapter XIV–XXII)—deals with graphical representation of planetary motion, astronomical instruments, spheres, and emphasizes on corrections and rejection of flawed principles.

Lalla also authored the Siddhāntatilaka.

Bhāskara II

1114 CE

Authored Siddhāntaśiromani(Head Jewel of Accuracy) and Karanakutūhala(Calculation of Astronomical Wonders) and reported on his observations of planetary positions, conjunctions, eclipses, cosmography, geography, mathematics, and astronomical equipment used in his research at the observatory in Ujjain, which he headed.

Śrīpati

1045 CE

Śrīpati was an astronomer and mathematician who followed the Brahmagupta school and authored the Siddhāntaśekhara(The Crest of Established Doctrines) in 20 chapters, thereby introducing several new concepts, including moon's second inequity.

Mahendra Suri

14th  CE

Mahendra Suri authored the Yantra-rāja(The King of Instruments, written in 1370 CE)—a Sanskrit work on the astrolabe, itself introduced in India during the reign of the 14th century Tughlaq dynasty.

Presents a fundamental formula along with a numerical table for drawing an astrolabe although the proof itself has not been detailed.

Longitudes of 32 stars as well as their latitudes have also been mentioned.

Mahendra Suri also explained the Gnomon, equatorial co-ordinates, and elliptical co-ordinates.

Nilakanthan Somayaji

1444–1544 CE

Revised Aryabhata's model for the planets Mercury and Venus. His equation of the centre for these planets remained the most accurate until the time of Johannes Kepler in the 17th century.

Nilakanthan Somayaji, in his Aryabhatiyabhashya, a commentary on Aryabhata's Āryabhatīya, developed his own computational system for a partially heliocentric planetary model.

He also authored a treatise titled Jyotirmimamsa stressing the necessity and importance of astronomical observations to obtain correct parameters for computations.

Acyuta Pisārati

1550–1621 CE

Sphutanirnaya(Determination of True Planets) details an elliptical correction to existing notions.

His another work, Karanottama deals with eclipses, complementary relationship between the sun and the moon, and 'the derivation of the mean and true planets'.

In Uparāgakriyākrama(Method of Computing Eclipses), Acyuta Pisārati suggests improvements in methods of calculation of eclipses.