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- Any discussion of Hindu cosmology would be empty without a discussion of astronomy and related sciences.
- As mentioned previously, the astronomical sciences appear as early as the Vedic period in the form of Jyotiṣḥśāstra, or "the science of light."
- Though there is considerable debate as to the range and nature of astronomical knowledge, it is known that the lunar mansions are mentioned in the Brāhmaṇas and that the Hindu science of calculation began with the cosmological Vedic altars and developed into the elaborate calculations of the yugas, kalpas, and mahākalpas in the Purāṇas. Jyotiṣḥśāstra encouraged thinkers to assign dates to the grand conjunctions of the middle planets at Aries, and the date February 18 (or 19) of 3101 (or 3102) bce is frequently cited as marking the beginning of the kaliyuga.
- One astronomical text, in the Viṣṇudharmottara Purāṇa (2:166–174), is the earliest of this genre and is the basis of the Brahmāpakṣa. Together with the Aryapakṣa and the Ardharatrikapakṣa, these three texts form the canonical schools of Hindu astronomy.
- The great astronomer-sage Āryabhaṭa (fifth–sixth centuries ce) calculated the rotations of the earth and the sun in terms of the yugas.
- His treatises (siddhantas) sketch his mathematical, planetary, and cosmic theories and include a sine table, astronomical computations, divisions of time, and rules for computation for eclipses as well as the longitude of planets.
- Among the other theorists, Varāhamihira (sixth century ce), Brahmagupta (seventh century ce), Bhāskara (twelfth century ce), and Mādhava (fourteenth century ce) all gave calculational and astronomical theories that contributed to overall ideas about the universe, such as the rotational powers of the planets and the centrality of the sun.
- Indeed by the time of Bhāskara (c. twelfth century ce) the old Purāṇic cosmology was being questioned with the construction of a different model of the solar system.
- In the debates one can detect a conflict between the Purāṇic cosmology and the cosmology of the Jyotiṣas.
- There are some discussions that remind one of the contemporary cosmological debate between creationism and the Big Bang.
- For instance, the astronomical writers asked: If, as some of the Purāṇas state, a tortoise is holding up the earth, then what being or substance might be supporting that tortoise? Or if one is assuming the gigantic height of Mount Meru and a flat, disk-like earth, then would not one be able to see Mount Meru from every point on the disk of the earth?
- Around 1200 ce al-Bīrūnī, an Arab astronomer and translator, noted the debates and problems of Purāṇic cosmology that were present in the discussions of Indian astronomers.
- Relatedly it is clear that there was a great deal of scientific collaboration between Hindus and Muslims in Mughal India, especially in seventeenth- and eighteenth-century Jaipur, where the appropriate description of the cosmos was argued out at great length.
- Finally, in the contemporary period various more and less controversial attempts have been made to correlate scientific advances with Hindu cosmology.
- In the more controversial cases textual exegetes argue about whether it is appropriate to view certain descriptions of "vehicles" in the epics as referring to space travelers or whether the ancient word yojana, mentioned above, refers to the speed of light.
- In a more speculative and less controversial vein Yoga theorists draw parallels between the theory of the three guṇas and James C. Maxwell's theories of electromagnetism; between the relation of space and time in Sāṃkhya theory and the theory of relativity; between the idea of the cosmic egg and the theory of curved space in the general theory of relativity; and so on.
- Many contemporary philosophers and historians, such as S. Radhakrishnan, B. K. Motilal, A. N. Balslev, and W. R. Kloetzli, have written of the parallels (not equivalencies) between scientific and Hindu philosophical thinking.
- The Hindu philosophical school of Nyāya Vaiśeṣika and its views on the atom's role in the universe is one particularly salient example.
- Finally, the cosmological writings of astrophysicist Jayant Viṣṇu Narlikar land more squarely in the world of physical science and cosmology.
- Considered a leading expert and defender of the steady state cosmology against the more popular Big Bang cosmology, Narlikar has also drawn some intriguing parallels with Hindu mythology—not in order to "prove" the existence of scientific knowledge in ancient texts but rather to show the power of the cosmological imagination in both science and mythology. Many of the cosmological myths referred to above, involving expansion and contraction, the in-breathing and out-breathing of Brahmā, and so on, seem to involve metaphors of a "steady state" similar to Narlikar's physical and mathematical arguments in scientific cosmology.