Indian astronomy is similar to its Chinese counterpart in that it has a long history, dating back as early as 2000 BC, possibly earlier. In its early stages, it was also used for keeping time and scheduling religious events, creating lunisolar calendar and astrological charts. Unlike Chinese, early Indian astronomy was accessible to ideas from early Babylonian, Greek and Persian civilisations and it was later influenced by Hellenistic world after the conquests of Alexander the Great. Later, after the golden age of Indian astronomy, the influence changed its direction and Islamic astronomy took a lot from what Indians knew and introduced that knowledge to Europe.
Earliest records available on Indian astronomy come from Hinduism’s sacred Vedic books, from which is also evident that cosmology and questions about how the Universe works were of interest to Indians. Since Vedic books are religious and not scientific texts, much of the information about early Indian knowledge of celestial objects is open for interpretation. The Shulba Sutras texts, part of appendices to the Vedas, discussed mathematics, geometry and astronomy in the context of altar building and are dated from 800 BC to 200 CE. Vedanga Jyotisha texts about astronomy and astrology originate from the 1st century BC, but are possibly based on traditions dating from 700 BC or older.
Early Indian calendars had 12 months each 30 days long for a 360 days in a year, but they added two extra time periods every five years to keep calendar and solar year the same. The year was then divided into six time periods based on ritual rites and seasons - spring, summer, rains, autumn, winter and dew.
The golden age of Indian astronomy came in the 5th and the 6th century with Aryabhata and his Aryabhatiya, meaning Aryabhata’s work, in 499 CE. In this text, Aryabhata set the start of each day at midnight and postulated that the Earth rotates around its axis and thus causes stars, the Sun and the Moon to apparently move westward in the sky. He was also aware that the Moon doesn’t shine, but merely reflects the sunshine.
By this time, Indian astronomy was separated from religion and is characterised by mathematical approach to astronomy. With Western civilisation stagnating and before the later advances of Islamic world, Indian astronomy was a pinnacle of world’s astronomy, backed by highly advanced mathematics.
Varahamihira, who also lived in this time period, was a mathematician and astronomer who studied Greek, Egyptian and Roman astronomy. He proposed that the same force is holding celestial bodies in place as well as holding us on the Earth, which we now know to be gravity. The 7th century astronomer and mathematician Brahmagupta also held this view. Brahmagupta also tried to measure the circumference of Earth, coming to 36,000 kilometres, just 10% less than the actual number.
Ancient and classical Indian astronomy relied more on computations than observations. I don’t mean they never observed celestial objects, just that compared to their observation techniques, their mathematics were far more advanced.
Indian astronomy began influencing China in the 1st-3rd century CE, but more significant influence came in time period from the 7th to the 10th century. Rich legacy of Indian astronomy and mathematics also expanded westward. With rise of Islam in the 7th century, a lot of knowledge from Indian astronomy and mathematics was incorporated into Islamic astronomy in centuries to come and later influenced European science. The computational techniques extensively used in Indian astronomy were fused with Islamic observational instruments to produce Islamic astronomical books, called Zijes.
The first Zij tablets in the 9th century were translated from Sanskrit. The Zijes contained computations of eclipses, astronomical and astrological computations, and later in the 17th century, during the Mughal Empire, they incorporated telescopic observations and heliocentric system.
With the arrival of the British, as India was colonised, the Indian astronomy had a profound effect on modern astronomy.
Today, India begins to emerge as a major player in space exploration, challenging another emerging country - China, their long time rivals in both astronomy, economy and culture. After the launch in 2013, their Mars Orbiter reached the Mars in September 2014 making India the first Asian country to reach Mars and fourth country/agency after Russians, USA and European Space Agency.