Sky has always been seen as the heritage of the whole humankind. People have been curious about their sky. They have also been curious about the curiosity of others. Accordingly, astronomy has advanced through pooling of intellectual resources and cross-fertilization of ideas. There is broad connectivity in the world history of astronomy. Astronomy is a multi-stage intellectual cumulus where each stage has built on the previous ones and carried the studies forward. The growth of astronomy has not occurred in a steady manner, but in spurts, with different centres playing a pre-eminent role at different times. An interesting correlation needs to be noted. The level and quality of astronomical activity has been related to a nation’s GDP. Prosperous, self-assured, resurgent, assertive nations have tended to become patrons of astronomy. It is as if having established their superiority or supremacy over fellow human beings, they wanted to unravel the mysteries of the sky on behalf of the whole humankind.

1. Sky as a bridge:
Astronomical interactions
in Eurasia through the ages
Rajesh Kochhar
President IAU Commission 41: History of Astronomy
Mathematics Department, Panjab University, Chandigarh, India
Indian Institute of Science Education & Research, Mohali, Punjab, India
rkochhar2000@gmail.com
Talk given at IAU General Assembly, Honolulu, 10 August 2015

2. • Sky has always been seen as the heritage of the whole
humankind. People have been curious about their
sky. They have also been curious about the curiosity
of others. Accordingly, astronomy has advanced
through pooling of intellectual resources and cross-
fertilization of ideas. There is broad connectivity in
the world history of astronomy. Astronomy is a multi-
stage intellectual cumulus where each stage has built
on the previous ones and carried the studies forward.

3. • The growth of astronomy has not occurred in a
steady manner, but in spurts, with different centres
playing a pre-eminent role at different times.
• The trajectory of development that culminated in
modern astronomy has a number of important
milestones: Mesopotamia (Iraq)
>Hellenistic world> India >Muslim
culture zone > Europe.

4. • China does not figure in the above sequence,
because it did not influence Europe. Also note that
the Roman empire did not contribute to astronomy,
but focused on law and engineering. This general
observation remains valid because Claudius Ptolemy
belongs to the Hellenistic tradition, even though his
epoch is c. 100 CE and place of work Rome.
• The reason for general Roman disinterest in
astronomy is probably this. Since astronomy was the
strong point of the Hellenistic Greeks whom the
Romans had vanquished, the new victors consciously
distanced themselves from it.

5. • At the same time , as a counter-example , it should
be noted that the 6th - 4th century BCE Persian
Achaemenid empire in Mesopotamia had no
difficulty in continuing the earlier astronomical
tradition.
• This raises an important question. When regime
changes, what activities are continued and what are
abandoned? What is the dynamics of continuity or
the break?

6. An interesting correlation needs to be noted. The
level and quality of astronomical activity has
been related to a nation’s GDP. Prosperous,
self-assured, resurgent, assertive nations have
tended to become patrons of astronomy. It is as if
having established their superiority or supremacy
over fellow human beings, they wanted to
unravel the mysteries of the sky on behalf of the
whole humankind.

7. This can be seen from recent developments. Europe’s
decline began with the First World War and the
centre of astronomical activity shifted to USA. After
the Second World War reconstruction, Europe,
unitedly this time, took to astronomy with renewed
vigour. Japan’s economic strength manifested itself
in its technology-backed astronomical projects. And
now, China , Korea and Japan together wish to
become an astronomical power.

8. • We can distinguish between two
successive phases in the human pursuit of
astronomy over the millennia: (i) the
geocentric phase, and (ii) the heliocentric,
telescopic phase. Interestingly, in both the
phases, the initial impulse came not from
love of stars but fear ; fear of the skies in
the first phase; and the fear of the waters
(that is, oceanic voyages before scientific
navigation), in the second phase.

9. • The first phase ended with Copernicus
who was a man of two parts. His
laborious mathematical work is in
continuation with that of his
predecessors. At the same time he
represents a drastic break with the past
by postulating the earth’s motion
around the sun.

10. • My concern here is with the first phase. Today, we
look at the universe as if from the outside. For us, it
is no more than a field station and a laboratory for
discovering natural laws and testing theories. In
earlier times, when the world was anthropo-centric,
cosmic environment was from human affairs. The
sky was partly a divinity to be feared and
appeased. Partly, it was a phenomenon to be
observed and utilized.

11. • As creator, God would surely keep a watch on the
Earthians. His messages and signals would be
communicated through movements in the sky.
• His wrath would be conveyed by the appearance
of unexpected phenomena, like comets, meteors,
and eclipses. They would call for post-facto
propitiation of the gods.
• Fortunately, the divine wrath was invariably
short-lived.

12. Planetary orbits represented cosmic order and
were a means of assurance of divine benevolence.
Ever increasing understanding of their orbits
decreased the distance between the human beings
and the divinities, and permitted the former to
establish an ex-ante (before the event) negotiatory
relationship with the latter.

13. • The beginnings of astronomy (and mathematics)
are related to the requirements of the ritual in
early cultures. Ritual was a means of securing
divine approval and support for terrestrial actions.
To be effective, it had to be elaborate and well-
timed, so that a careful distinction could be made
between auspicious and inauspicious times. Since
planetary orbits were the timekeepers provided by
nature, their study became important.

14. Egypt and Babylonia
• Alexander’s (356-323 BCE) military campaigns
against the Persian empire which began in 334
BCE and brought him up to river Indus in the
Indian subcontinent paved the way for intellectual
interaction over a vast region. After his death,
Greek-speaking dynasties came to power in Egypt
(Ptolemaic, in 323 BCE) and Mesopotamia
(Seleucid, in 312 BCE).

15. • Both these countries had an older civilization ,
big food surplus, vast geography, and high levels
of practical knowledge and technological
developments. The combination of these with the
classical Greek intellectual tradition produced
remarkable results of long-lasting value.

16. • Alexandria in Egypt was founded in 331 BC and
emerged as a major centre for scientific activity.
The vastness of Egypt made possible the
celebrated experiment by Eratosthenes (c. 275-
192 BC) to measure the circumference of the
earth, using Alexandria and Aswan ( modern
name) as reference stations. (Similarly, the
vastness of British India permitted the
measurement of the great meridional arc under
George Everest.)

17. • Scientific activity in Alexandria came to an end
in 144 BC, when the king Ptolemy VIII expelled
all intellectuals and scholars from the city.
Alexandria itself was conquered by the Romans in
30 BC. The Egyptian solar calendar travelled to
Europe with the Romans and became the basis for
Julian/Gregorian calendar.

18. • In Babylonia, the Greeks had the advantage of
inheriting a rich and well-preserved astronomical
tradition. Babylonia had maintained a tradition
of making and recording astronomical
observations and a mechanism (cuneiform) for
storing and preserving the records. The Greeks
could use records going back to 8th century BCE

19. • I think it needs to be appreciated that the Greco-
Babylonian astronomy was characterized by a
combination of continuity and break. The Greeks
had now access to old data which had been taken
by others. They could pursue astronomy as an
intellectual discipline without being overwhelmed
by its divine dimension. India, for instance, could
never really decouple scientific astronomy from
the sacred.

20. • An accurate luni-solar calendar (with seven extra
months in 19 years) was introduced in Babylonia
in 383 BCE (Ref. 1). During the Achaemenid
period itself, 12-equal part zodiacal belt was
introduced (Ref. 2). The seven-day week, inspired
by the seven planets, butwith its peculiar ordering
of days, was a much older construct, from
Chaldean times. They all now became known in
the outside world.

21. India
• Greco-Babylonian astronomical elements were
brought into India from the northwest by the
Indo-Greeks. Through a long-drawn and hardly
understood process, they were incorporated into
the Indian mainstream. Revitalized Indian
mathematical astronomy (known as Siddhantic
astronomy ) appears in a full-blown form in the
499 CE text composed by Aryabhata.

22. • The Siddhantic tradition remained active for more
than a thousand years. The most remarkable
feature of ancient Indian astronomical tradition
was the development of approximate
mathematical solutions for astronomical
calculations. Thus Diophantine and Pell
equations were solved. In the 14th century
Kerala-based astronomers ( Madhava) discovered
infinite series for sine, cosine and arctangent
functions and for pi.

23. • The European names associated with these
‘discoveries’, made more than 200 years later, are
Colin Maclaurin, Isaac Newton, James Gregory
and Gottfried Wilhelm Leibniz. The European
names associated with these ‘discoveries’, made
more than 200 years later, are Colin Maclaurin,
Isaac Newton, James Gregory and Gottfried
Wilhelm Leibniz. Appreciation of pioneering
mathematical work in the astronomical context is
a recent phenomenon.

24. • In its own time, the influence of Siddhantic
astronomy spread westwards as well as eastwards.
• Even though Siddhantic astronomy received new
inputs from Greco-Babylonian astronomy ( including
an accurate luni-solar calendar, week and zodiac),
many features of the old, Vedic, astronomy were
advisedly retained. The moon’s position at night was
marked with respect to bright stars/ star groups
(known as nakshatras) visible near it. The number
originally was 28 , but was later brought down to 27.

25. • Both the Chinese and the Arabs have a similar
system, respectively known as Hsiu and Manzil,
comprising 28 names. The Indian as well as the
Arabic list begins with Beta Arietis, which
marked spring equinox in about 300 CE. The first
entry in the Chinese list is Alpha Virginis, which
marked the autumn equinox at the same epoch.

26. • There is an interesting interplay between
scriptures, astronomy and mythology in the case
of eclipses which needs to be noticed because of
its transmission outside India.
• Mythology was upgraded to keep pace with
astronomy. Astronomy in turn adopted
mythological terms to maintain continuity with
scriptures.

27. • Post-Rigveda Vedic mythology attributed eclipses
to a demon called Rahu. Even when scientific
cause of the eclipses became known, the demon
was not banished, but accommodated in the new
scheme of things.
• The demon was cut into two, so that the head and
torso corresponded to the ascending and
descending lunar nodes, respectively. They were
designated Rahu and Ketu.

28. • Indian mythology now had demons who
came by appointment!
• Athe term Keru was an old one given an extra
meaning. Vedic mythology used the term ketu to
denote comets, meteors, etc. (Ref. 3). It continued
to be used in that sense also.

29. Muslim culture zone
• In later Iranian (and Arabic) mythology the Rahu
and Ketu become the head and the tail of the
dragon Al –Djawzahr. Ketu as comet came to be
known as al-Kayd (Ref. 4).
• Of greater significance was the incorporation of
Indian scientific astronomy into Arabic science.

30. • In about 773 CE, al-Fazari, on orders from the
second caliph al-Mansur (reign 754 -775 AD)
translated a Sanskrit astronomical text into
Arabic. This was the Arabia’s first introduction to
the Indic numerals. Historically, far more
significant is the work of the mathematician al-
Khwarizmi who flourished during the reign of
caliph al-Mamun ( reign 813-833 CE) and
became the conduit for transfer of Indian
mathematical knowledge to Europe.

31. • The significance of al-Khwarizmi’s work can be
quickly seen from the fact that the English
language owes three common terms, algebra,
(trigonometrical) sine and algorithm, to 12th
century Latin translation of his works.

32. • The term Algebra comes from the title of his book
which contains the Arabic word al-jabr.
• The Latin/English term sine comes from his algebra.
Indian astronomy introduced the term jya , which
literally meant a bowstring and was given the
technical meaning of half-chord. Also called jiva, it
was rendered in Arabic as jaib. Now, jaib was an
existing word in Arabic meaning fold of a dress; this
was literally translated as sinus in Latin.
• In the translation of al-Khwarizmi’s book on
arithmetic, his name was Latinized to Algoritmi
which in turn gave rise to the term algorithm.

33. China, Korea, and Japan
• While India’s interaction with the Muslim culture
zone was two-way, interaction with east Asia and
southeast Asia was largely unidirectional. Indian
influences reached China by land and further to
Korea and Japan. There was an independent
channel to Tibet. East India was in regular touch
with Indonesia, Thailand, Burma, etc. through
sea.

34. • Buddha personally was firmly against astrology,
so that while Buddhism flourished in India,
astronomy went into decline. By the time
Buddhism was exported to East Asia, astronomy/
astrology had become part of it. Unlike the
traditional Chinese focus on portents, Indian
mathematical astronomy could prepare
horoscopes for the benefit of individuals.

35. • Interaction with east Asia was driven by
Buddhism and was characterized by translation of
Buddhist and other texts. It began in the first
century CE during the Later Han period (25–220
CE) and continued into the politically unstable
Three Kingdom period (220-265 CE).

36. • Indian inputs continued intermittently even after
that, with the most detailed incorporation of
Indian astronomy coming during the Tang
Dynasty (618-906 CE). Indian-origin documents
found in China and Tibet are important from the
point of view of history of India also, because
they provide textual information which carries a
firm date.

37. • Notwithstanding earlier pre-Siddhantic (pre-499 CE)
translations, China’s systematic introduction to Indian
astronomy began in early 8th century. Unlike in India,
where almanac-making was a social/religious affair,
in China it enjoyed state support. An astronomer of
Indian descent Qutan Xida [Gautam Siddha] prepared
an astronomical treatise, Jiu-zhi-li in 718 CE. Its
elements in turn were employed by the well known
Chinese astronomer Yi-Xing (687-727 CE) in his
famous calendar Da-yan-li.

38. • Far more significant was the contribution of the
Indian Buddhist monk, Jin Ju Zha, whose Qi Yao
Rang Zai Jue contains detailed ephemerides of
Rahu and Ketu. It was incorporated into
calendrical calculations of the Tang dynasty
Yuanhe era, Year I (806 CE).

39. • Being 180 degrees apart, the nodes Rahu and
Ketu are not independent variables. Recognizing
this, Jin Ju Zha’s while employing Rahu to
denote the ascending node, boldly decided to use
Ketu to denote lunar apogee (Ref.5). This shows
that Indian astronomical influences were not
superficial, but became part of the Chinese
mainstream.

40. The making of Copernicus
• As we know, planetary orbit calculations became
very simple once Kepler enunciated his laws and
introduced the concept of elliptical orbits. Before
that, Ptolemy’s mathematical model for
calculating planetary orbits by using circles alone
remained influential for a very long time. One
aspect of Ptolemy’s model, the equant, which
permitted non-uniform circular motion, was
recognized as a problem.

41. • An important astronomical development was the
1269 CE establishment of the Maragha
Observatory ( East Azerbaijan, Iran) which
preceded Ulugh Beg’s Samarqand Observatory by
150 years. Important names associated with
Maragha are al-Tusi (1201-1274), al-Urdi (d
1266), al-Shatir ( d. c. 1375), and al-Khafiri (fl
1525).

42. • Did the Maragha work on improving Ptolemy model by
such theoretical constructs as al-Tusi couple and al-Urdi
lemma remain a dead end or did it influence later
developments?
• There is no doubt that Copernicus’s planetary models
exhibit some striking similarities to those of the
Maragha astronomers. Did Copernicus know of the
previous work or did he develop his model entirely
independently? The question has been discussed for the
last seven decades. The general opinion seems to be that
Copernicus was indeed influenced by Maragha (Ref. 6) .
However, Copernicus’ independence is still being argued
for (Ref. 7).

43. • Copernicus explicitly cites five Islamic scholars,
but they all belonged to 12th century CE or
earlier. He does not quote any later author. This
however does not necessarily mean that he did
know of their work. Copernicus’ target audience
was Europe. He would quote authors who were
part of a learned man’s library in Europe. He may
have consulted obscure works and not cited them.

44. • Was the work of al-Tusi and others available in
Europe? It was. Al-Tusi’s models seem to have
been known to Copernicus’ contemporaries, like
Giovanni Battista Amico and Girolamo
Fracastaro. A Greek manuscript, probably dating
from 13th century and in the Vatican since the
15th century, mentions al-Tusi’s work. This also
could have been seen by Copernicus (Ref. 6).

45. • To me, it appears natural that a researcher
addressing a difficult problem of long-standing
duration would first of all acquaint himself with
the work done before him. Whether Copernicus
re-invented al-Tusi couple or not, his laborious
mathematical work is in continuation with that of
his predecessors. The break with the past came
not from his calculations but from his hypothesis
that the earth goes around the sun.

46. Concluding remarks
• History of astronomy (and science) was
particularly important for the 19th century
Europe. As authors of the powerful knowledge
system of modern science, Europeans claimed
cultural and racial superiority, and by extension
right to rule, over others. Accordingly, as an
article of faith, the origin of modern science and
the entire trajectory of its development were
placed within the geographical limits of Europe.

47. • In this framework, an unresolved monolithic
period of antiquity was created that extended
from the 6th century BCE ( Greek philosopher
Thales) to 2nd century CE ( Greek astronomer
Ptolemy).
• No distinction was made between the Hellenic
and the Hellenistic phases; and there was no
question of investigating the antecedents of the
Hellenistic science. It is noteworthy that in
the hybrid Hellenistic period, the classicist
Aristotle did not enjoy the type of reputation
Europe bestowed on him later.

48. • In 1819, a British text book writer in India paid
glowing tributes to al-Tusi’s commentary on
Euclid , already popular in India, saying that it
had been enriched ‘ with great variety of
explanatory notes, new demonstrations, and
additional propositions, which cannot fail to be
studied with advantage by all who wish to enter
deeply into the science themselves, or explain its
principles to others’ .

49. • And yet, in the Arabic-language text book he was
writing for students in government-run madrasas (
traditional Muslim school), he removed ‘all that is
not Euclids’ so as ‘to guard the accuracy of the
text’ (Ref. 8). It is remarkable that Muslim
students were to be told about Euclid but not
about the contribution of Muslim scientists who
carried on from him.

50. • Similarly, Indians were informed that there was
nothing original in their astronomy, and that it was a
tame imitation of the Greek. This put Indians
perennially on the defensive. As recently as 1970, an
otherwise well-regarded Indian historian of
astronomy tamely submitted that the borrowings
from the Greeks were in astrology rather than
astronomy (Ref. 9), as though the distinction made
any sense while talking of 2000 years ago.

51. • The next challenge to European historical
ingenuity was presented by India’s contributions
to chemistry. The author of an ancient Sanskrit
chemistry text (Rasa-sara ) declared in the
colophon at the end of the text that he had
composed the work after consulting the traditions
and opinions of the Buddhists. Commenting on
it, the British experts declared with a straight face
that that by Buddhists, ‘the author probably meant
the Muhammadans’ (Ref. 10).

52. • Surely Arabs would have liked to hear that. But
they were instead told that their role in the world
history of science had been no more than as
librarians and archivists for preserving Greek
science till Europe was in a position to take its
heritage back.

53. • The American philosopher, Thoreau, made a very
perceptive observation: ‘A man is wise with the
wisdom of his time only, and ignorant with
its ignorance’.
• Euro-centric historiography was consistent with
Europe’s requirements and philosophy of the 19th
century. Anti-Euro-centrism and ultra-nationalism
would be a continuation of the same.

54. Cultural Copernicanism
• The theoretical framework that I have developed
for historical analysis of the colonial period can
be described as Cultural Copernicanism.
Cosmological principle, named in honour of
Copernicus, states that the universe does not have
any preferred direction or location. Its cultural
counterpart part would similarly assert that no
cultural, geographical or ethnic area can be
deemed to be a benchmark to be used to evaluate
and judge others. This framework manifestly
rejects Euro-centrism as well as anti-Euro-
centrism.

55. • What we need is a world
history of astronomy,
written with rigour and
detachment and on behalf
of the whole humankind.

56. Thank you

57. References
1. Fotheringham, J.K. (1934) The Calendar in The
National Almanac for 1935 (London: H.M.
Stationery Office), pp. 754-770; see p.756
2. Evans, James (1998) The History and Practice of
Ancient Astronomy (New York: Oxford), p. 15
3. Kochhar, Rajesh (2010) Rahu and Ketu in
mythological and astronomological contexts.
Indian Journal of History of Science, Vol 45, pp.
287-297.

58. 4. Hartner , W. (1965) Al-Djawajahar. Encyclopedia
of Islam, Vol. 2 (Leiden: Brill), pp. 501-502.
5. Niu, Wei-Xing (1995) ‘An inquiry into the
astrological meaning of Rahu and Ketu.’ Chinese
Astronomy and Astrophysics, Vol. 19, No. 2, pp.
259-266.
6. Ragep, F. Jamil (2007) Copernicus and his
Islamic predecessors: Some historical remarks.
History of Science, Vol. 45, pp. 66-81.
7. Blasjo, Viktor (2014)A critique of the arguments
for the Maragha influence on Copernicus. Journal
of History of Astronomy, Vol. 45, pp. 183-195.

59. 8. The Second Report of Calcutta School Book
Society’s Proceedings, 1819, App. IV, p. 37.
9. Chatterjee, Beena ( 1970), The Khandakhadyaka
of Brahmagupta, Vol. 1 ( Delhi: Motilal
Banarasidass), p. 290.
10. Ray, Prafulla Chandra (1918) Essays and
Discourses (Madras: G.A. Natesan), p. 91.