ISRO is at the centre of international attention and acclamation after the launching of Chandrayaan-2, India’s second moon mission with a plan to land the rover on September 7 on the moon’s unexplored South Pole. It is being seen as a giant leap in India’s ambitious, low-cost space programme and is the most complex and prestigious mission ever undertaken by the ISRO. As such, India’s accomplishment is keeping in line with the astronomical achievements that India has been associated with, in the past. Since ancient times, the Indian subcontinent has been extremely progressive when it comes to astronomical discoveries, which is visible through the records and findings by the archaeologists.
Vedanga Jyotisha is one of the earliest known Indian texts on astronomy, authored by Lagadh. The text is foundational to the Vedanga discipline of Jyotisha. Jyotisha, focusing on timekeepingastronome, is one of the 6 auxiliary disciplines of Hinduism, collectively forming the Vedanga. The text describes rules for tracking the motions of the sun and the moon. There are many debates as to the time of its origin, with some scholars supposing the date of the text as 1370 and 1150 BCE, some claiming 1400-1200 BCE and others proposing the date as 700-600 BCE. Irrespective of any scenario, it is clear that the text was advanced way beyond its years. Vedanga Jyotisha portrays the sophisticated horoscopic astrology and advanced astronomical knowledge possessed by the Indians during the early age.
Aryabhatta was one of the first major mathematician-astronomers during the years 476-550 CE. Arguably the greatest Indian mathematician of all time; his works include the Āryabhaṭīya and the Arya-siddhanta. His system of astronomy was called the audAyaka system, in which he stated that the day begins at dawn at equator. Contrary to the then prevailing mindset, Aryabhatta calculated that it’s not the sky which rotates but it is the earth which rotates about its axis daily. He believed the planet’s orbits to be elliptical rather than circular and impressively calculated earth’s sidereal rotation as 23 hours, 56 minutes, and 4.1 seconds. The modern value of rotation is 23:56:4.091.
He also gave correct positions and speeds of the planets in the sky in terms of the mean speed of the Sun, which was viewed by some scientists as an underlying heliocentric model, as opposed to the geocentric model which was widely accepted during those times. Solar and lunar eclipses were scientifically explained by Aryabhatta by stating that the moon and the plants shine by the reflected sunlight.
Aryabhatta’s work was not only was an influence on the Indian astronomical studies but was also widely used by the Islamic and Western cultures.
Brahmagupta, who came a few years after Aryabhatta between 598-668 CE, is best known for his methods of calculating the position of heavenly bodies over time. He wrote an astronomically treatise titled Khaṇḍakhādyaka. He was the first to rebut that the moon was farther from the Earth than the Sun and explained that actually moon is closer to the earth than the sun. His work further explores the longitudes of the planets, diurnal rotation, lunar and solar eclipses, risings and settings, the moon’s crescent and conjunctions of the planets.
Varāhamihira, an astronomer in the early 6th century CE, is best known for his most notable work, Brihat Samhita, an encyclopedia containing information on various topics including planetary motions, eclipses, timekeeping, astrology and seasons. He learnt the Greek language to understand the works of the Greek scientists and introduced those works in the Indian subcontinent. His main astronomical work, Pañcasiddhāntikā, summarises five earlier Indian astronomical treatises which are now lost. His works and theories are some of the earliest to have survived
Bhaskara I, was a 7th-century mathematician astronomer whose commentary, Āryabhaṭīyabhāṣya is among the oldest known prose works in Sanskrit on the subject. His 2 works on astronomy, Mahābhāskarīya and the Laghubhāskarīya are on the lines of Aryabhatta’s work. His most noted work has been the introduction of numbers in the Hindu decimal system, with a circle for zero. Prior to him, the astronomers used words instead of symbols for numbers.
Lalla was a mathematician, astronomer and astrologer from the 8th century. His most famous work was titled, Śiṣya-dhī-vṛddhida-tantra which draws onto the earlier teaching of astronomers such as Āryabhaṭa I, Bhaskara I and Brahmagupta, with significant innovations. He combined the teachings on the two and delved into the computation of the position of planets, syzygies, eclipses and gave the earliest known description of perpetual motion.
After the era of the 8th-century astronomers, came another great mathematician- Sripati, in the 11th century. Out of his works, 3 contain astronomical verses which are, Dhikotidakarana, Dhruvamanasa and Siddhantasekhara. These contain verses on calculating planetary longitudes, eclipses and planetary transits, solar and lunar ecliples and other astronomical calculations. He also wrote extensively on astrology, and his work Jatakapaddhati, which contributed immensely to the computation of the strengths of the planets and astrological places, was used by astrologists long after his time.
Another great mathematician-astrologer Bhaskara II came into the picture in the 12th century. He was referred to as Bhaskaracharya, meaning, Bhaskara the teacher. Out of his celebrated works, the Ganitadhyaya deals with mathematical astronomy which is based on the earlier work by Aryabhata. Likewise, Bhaskara viewed the solar system as being heliocentric, and that the planets have an elliptical orbit. Considered as one of the greatest astronomers, Bhaskara also used the law of gravity that was proposed by Brahmagupta. In his book, he further examined the longitudes and latitudes, the conjunction of the planets as well as the orbits of the sun and the moon. Without having access to any sophisticated equipment, Bhaskara calculated that it would take 365.2588 days for the Earth to orbit the Sun. Today’s calculation is 365.2596 days, making his predication nearly accurate.
These were the ancient and medieval era astronomers who contributed much to the later scientists in the modern era, in India and all over the globe. In light of such tremendous accomplishment by the ISRO, it is pertinent that these great personalities are remembered and paid homage to.