Light with a speed, long before Maxwell
For most of the history of European physics it was an open question whether light moved at all. Aristotle held that vision was instantaneous; Descartes still argued for infinite speed in the 17th century. Only with Rømer's observations of Jupiter's moons, and later the field equations of James Clerk Maxwell and the relativity of Albert Einstein, did a finite, fixed velocity for light become settled science.
The Indian astronomical tradition never entertained the hesitation. Its Siddhānta texts computed eclipses, conjunctions and the visible positions of planets, and those computations only close if the light carrying an event to the observer takes a measurable time to arrive. Finite light was not a philosophical position in this tradition — it was a working assumption inside the arithmetic.
The granular mathematics of Sāyaṇa
The most explicit statement of that assumption comes from Sāyaṇa (c. 1315–1387 CE), minister and scholar of the Vijayanagara Empire and author of the great commentary on the Ṛgveda. Commenting on Ṛgveda 1.50.4 — a hymn addressed to Sūrya, the Sun — he gives what reads as a kinematic formula for the motion of sunlight.
तथा च स्मर्यते योजनानां सहस्रे द्वे द्वे शते द्वे च योजने एकेन निमिषार्धेन क्रममाण नमोऽस्तु ते॥
tathā ca smaryate yojanānāṁ sahasre dve dve śate dve ca yojane ekena nimiṣārdhena kramamāṇa namo'stu te
'It is remembered thus: O you who traverse 2,202 yojanas in half a nimiṣa — salutations to you.'
To test the claim, the two ancient units have to be mapped onto modern ones. Both mappings come from within the tradition's own texts:
- 1 yojana (distance) — as defined in the Viṣṇu Purāṇa · ≈ 9.09 miles
- 1 nimiṣa (time) — as defined in the Mahābhārata · 16/75 of a second
- half a nimiṣa (Δt) · 8/75 of a second
Substituting into ordinary velocity, distance over time:
c = Δd ÷ Δt = (2,202 × 9.09) ÷ (8/75) ≈ 187,670 miles per second.
Detailed close-up of a rustic ancient measuring instrument — a copper water-clepsydra used for tracking nimiṣas, fractions of a second — resting on a stone table etched with Sanskrit numerals and geometric arcs, lit warmly from one side.
Send: essay-measuring-heavens-clepsydra.jpg
The academic caveat
Modern physics fixes the speed of light in vacuum at 186,282 miles per second. Sāyaṇa's figure sits within one percent of it.
That closeness should be read carefully. The length of a yojana was not standardised across regions and eras — estimates range from roughly 5 to 9 miles — so the arithmetic is sensitive to which value is chosen, and a sceptic can reasonably call the fit fortunate. What is not in doubt, and is the more interesting claim, is the framework: a tradition working with time-fractions on the order of a tenth of a second, applied to a cosmic quantity, and stating the result as a rate. That is a kinematic habit of mind, several centuries before the European Enlightenment made it standard.
Orbital mathematics inside devotional poetry
The second case shows how such constants were stored. In this tradition hard astronomical numbers were rarely left to the Siddhāntas alone — technical manuals circulate among specialists and are lost with them. Numbers woven into hymns that whole populations recite daily survive instead in cultural memory.
The Hanumān Cālīsā, composed by the poet-saint Tulsīdās in the 16th century CE, is recited across northern India as a prayer of protection. Its 18th verse describes the child Hanumān leaping toward the Sun — and states the distance he crossed.
जुग सहस्र जोजन पर भानू। लील्यो ताहि मधुर फल जानू॥
yuga sahasra yojana para bhānū, līlyo tāhi madhura phala jānū
'The Sun, a yuga times a thousand yojanas away, you swallowed, taking it for a sweet fruit.'
Macro shot of the pages of an antique illuminated Awadhi manuscript of the Hanumān Cālīsā, the words 'yuga sahasra yojana' glowing faintly, with delicate geometric constellations drawn in the margins.
Send: essay-measuring-heavens-chalisa-manuscript.jpg
Yuga · sahasra · yojana
Read as poetry, the line is hyperbole. Read against the numerical conventions of classical Hindu cosmology, each of its three terms is a fixed constant:
- yuga — one complete celestial cycle (Satya, Tretā, Dvāpara, Kali) · 12,000 divine years
- sahasra — the Sanskrit multiplier · 1,000
- yojana — the localised unit of distance · ≈ 8 statute miles
Taking the product:
D = yuga × sahasra × yojana = 12,000 × 1,000 × 8 = 96,000,000 miles.
Awe-inspiring mythological-meets-scientific illustration: a massive glowing sun suspended in space with luminous orbital rings mapping its distance from Earth, and in the foreground a stylised silhouette of Hanumān leaping upward, leaving a trail of golden Sanskrit mathematics in his wake.
Send: essay-measuring-heavens-hanuman-leap.jpg
The academic caveat
Modern telemetry puts the Astronomical Unit — the mean Earth–Sun distance — at about 93 million miles, varying between roughly 91.4 and 94.5 million across the elliptical orbit. The verse's 96 million falls just outside the far end of that range.
No one is claiming Tulsīdās owned a telescope. The claim is one of inheritance: he was the beneficiary of an astrophysical tradition already centuries old — the Sūrya Siddhānta (c. 400 CE), the Āryabhaṭīya of Āryabhaṭa, the corrections of Brahmagupta and Bhāskara — and he did something specific with it. He translated orbital arithmetic into vernacular Awadhi verse, and by doing so kept it in circulation among people who would never read a Siddhānta.
For the observational tradition these numbers came out of, see [Vedic Devas and cosmology](/essays/vedic-devas-cosmology) and the astronomers gathered under [Luminaries](/luminaries). For the Sun's own theology, and for the child who leapt at it, see [Śrī Hanumān — the lore](/essays/hanuman-lore).