🔭 Astronomy in Bharat
Shadow clocks and water clocks, Aryabhata and Varahamihira, Brahmagupta and the Kerala School, the stone instruments of Jantar Mantar, and India’s observatories in the mountains and in space.
⏳ Measuring time and the sky
Shadows, water and reflections: the first instruments of Indian astronomy.
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2nd century BCE – 3rd century CE
Shadow clocks and water clocks
The earliest reference to measuring time by shadows is in Kautilya’s Arthasastra, which also describes a water clock with water flowing out.
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Aryabhata’s time
The Ghatika-yantra (sinking-bowl water clock)
Because outflow clocks slowed as the water dropped, a sinking-bowl water clock was developed — first mentioned by Aryabhata. It kept time at monasteries, palaces and town squares, where each sinking of the bowl was announced; the day was divided into 60 ghatis.
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around 530 CE
Time from a stick’s shadow
Varahamihira gave an accurate expression for time in terms of the shadow of a vertical stick.
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Bhaskara II’s time
Watching the sky in bowls of water
More than 800 years ago, astronomers looked at stars and planets reflected in shallow bowls of water, through tubes set at the right angles, to measure their positions.
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The Surya Siddhanta and eclipses
Many Indian astronomical texts give calculations to predict eclipses; the best known is the Surya Siddhanta, written in rhythmic Sanskrit shlokas. The Indian National Calendar adopted in 1956 follows its general principles.
🪐 The classical astronomers
From Aryabhata’s spinning Earth to the Kerala School’s infinite series.
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around 500 CE
Aryabhata and the Aryabhatiya
A short treatise of mathematics and astronomy. Aryabhata proposed that the Earth spins on its axis, gave the length of the year within minutes of the modern value, estimated the size of the Earth and correctly explained solar and lunar eclipses. His value for one rotation of the Earth is about 23 hours 56 minutes 4.1 seconds.
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Gupta period
Varahamihira’s Brihat Samhita
An encyclopedic work covering astronomy and astrology, weather forecasting, architecture, town planning and even farming.
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Born 598 CE
Brahmagupta and the Brahmasphutasiddhanta
Born in Bhillamala, Brahmagupta had remarkable achievements in mathematics and astronomy; in the Brahmasphutasiddhanta he set out the rules of arithmetic with zero, negative numbers and fractions.
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11th century
Al-Biruni studies Indian science
Al-Biruni learnt Sanskrit and wrote an encyclopaedic survey of India, compiling in mathematics and astronomy what he could gather from the works of Aryabhata, Varahamihira and Brahmagupta.
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14th century
Madhava and the Kerala School
Madhava made pioneering contributions to calculus, including the series expansion for trigonometric functions — a world first. He and his followers are known as the Kerala School of Astronomy and Mathematics, which produced important works until the 19th century.
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1500
Nilakantha Somayaji’s planetary model
A scholar of the Kerala School worked out a planetary model in which Mercury and Venus went round the Sun.
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About 300 years ago
The Samrat Yantra at Jantar Mantar
The world’s largest stone sundial, 27 metres high, at the Jantar Mantar in Jaipur — a UNESCO World Heritage site with several astronomical instruments. Its scale measures intervals as short as 2 seconds.
🛰 Modern astronomy and space
A national calendar, a dark-sky reserve in Ladakh, and observatories and probes in space.
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21 March 1956
The Indian National Calendar
A Calendar Reform Committee chaired by Meghnad Saha recommended a unified national calendar, adopted from 1 Chaitra 1878 Saka; it follows the general principles of the Surya Siddhanta.
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19 April 1975
Aryabhata, India’s first satellite
Named after the astronomer, it was completely designed and fabricated in India and launched by a Soviet rocket.
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28 September 2015
AstroSat, India’s space observatory
India’s first dedicated space astronomy observatory, with five payloads that observe the same source at once from far ultraviolet to gamma rays.
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22 July 2019
Chandrayaan-2
An orbiter, lander and rover to explore the unexplored south pole of the Moon — a significant technological leap for ISRO. It entered lunar orbit on 20 August 2019.
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December 2022
Hanle Dark Sky Reserve
The area around the Himalayan Chandra Telescope — named after Subrahmanyan Chandrasekhar, at one of the highest observatories in the world — was notified as a dark sky reserve.
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2 September 2023
Aditya-L1 studies the Sun
A satellite dedicated to the comprehensive study of the Sun, with seven indigenously developed payloads, placed near the L1 point between the Earth and the Sun.
How we check: every entry is from an NCERT textbook or an ISRO mission page; our build fails unless its key phrases are found in the source itself. Most entries are shared with the Science pages.