The Ujjain Observatory, also known as the Vedhshala, is considered to be the oldest known observatory in India. It was established in the 5th century BCE and was used for astronomical observations and calculations.

Varāhamihira, a renowned Indian astronomer and mathematician, is credited with establishing the Ujjain Observatory in the 5th century BCE. He used the observatory to make significant observations and calculations related to astronomy and astrology.

The Ujjain Observatory was equipped with various instruments for astronomical observations, including the astrolabe, sundial, and quadrant. These instruments were used to measure the positions of celestial bodies, calculate time, and study the movements of planets and stars.

One of the notable discoveries made at the Ujjain Observatory was the precession of the equinoxes. This refers to the gradual shift in the position of the equinoxes, which are the two points on the celestial sphere where the ecliptic (the Sun's path) intersects the celestial equator. This discovery was significant in understanding the long-term motion of the Earth's axis.

Jai Singh II, the Rajput king of Jaipur, is credited with the construction of five Jantar Mantar observatories in India. These observatories were built in the early 18th century and served as centers for astronomical observations and calculations.

The Jantar Mantar observatories were designed to serve multiple purposes. They were used for measuring the time of day, tracking the movement of stars and planets, predicting eclipses and other celestial events, and studying various astronomical phenomena.

The Jantar Mantar observatories feature a variety of instruments, including the Samrat Yantra (a large sundial), the Rashivalaya Yantra (a zodiac instrument), and the Jai Prakash Yantra (a complex instrument for measuring time and tracking celestial bodies).

The primary objective of the Nalanda Observatory was to observe the movement of planets and stars. It was used to study the positions, motions, and relationships between celestial bodies, contributing to the advancement of astronomical knowledge.

Aryabhata, a renowned Indian astronomer and mathematician, is associated with the Takshashila Observatory. He made significant contributions to astronomy and mathematics, including the development of the Aryabhata system, which introduced the concept of zero and the decimal system.

Aryabhata made several notable achievements at the Takshashila Observatory, including calculating the value of pi (π) with remarkable accuracy, deriving the formula for the area of a triangle, and developing a method for solving quadratic equations.

The British established several observatories in India during their colonial rule, including the Madras Observatory, the Kodaikanal Observatory, and the Udaipur Solar Observatory. These observatories played a significant role in advancing astronomical research and contributing to the development of modern astronomy in India.

The Madras Observatory primarily focused on stellar spectroscopy, which involves studying the light emitted by stars to understand their physical properties, chemical composition, and behavior.

M. K. Vainu Bappu, a renowned Indian astronomer, made significant contributions to solar astronomy at the Kodaikanal Observatory. He conducted extensive studies of sunspots, solar flares, and other solar phenomena, helping to advance our understanding of the Sun's activity and behavior.

The Udaipur Solar Observatory was established with the primary purpose of observing sunspots and solar flares, studying the Sun's magnetic field, and measuring the Sun's temperature and luminosity. These observations contributed to a better understanding of solar activity and its impact on Earth's climate and space weather.

The Giant Metrewave Radio Telescope (GMRT) is a radio astronomy observatory located near Pune, India. It is one of the world's largest radio telescopes and is dedicated to studying the universe at radio wavelengths, allowing astronomers to explore various celestial objects and phenomena.