The Ujjain Observatory was built in the 5th century BCE and is considered to be the oldest known astronomical observatory in India.

Varāhamihira was a famous astronomer who worked at the Ujjain Observatory in the 6th century CE. He wrote several important works on astronomy, including the Brihat Samhita.

The Jantar Mantar is an astronomical observatory built by Maharaja Jai Singh II in the 18th century. It consists of a collection of architectural instruments designed for astronomical observations.

A quadrant is an instrument used to measure the altitude of celestial objects. It consists of a quarter-circle arc with a plumb line attached to the center.

A sundial is an instrument used to measure the time of day. It consists of a pointer that casts a shadow on a marked surface.

An astrolabe is an instrument used to measure the position of celestial objects in the sky. It consists of a circular disk with a series of concentric circles and lines.

An armillary sphere is an instrument used to represent the celestial sphere. It consists of a series of concentric rings that represent the different celestial circles.

The Surya Siddhanta is the most important astronomical text written in ancient India. It was written by an unknown author in the 5th century CE and contains a wealth of information about astronomy, including the positions of the planets, the length of the year, and the causes of eclipses.

Pi is the astronomical constant that represents the ratio of the circumference of a circle to its diameter. It is approximately equal to 3.14.

Ursa Minor is the constellation that contains the North Star. It is located near the North Pole and is visible from both the Northern and Southern Hemispheres.

Sirius is the brightest star in the night sky. It is located in the constellation Canis Major and is visible from both the Northern and Southern Hemispheres.

The Milky Way is the galaxy that contains the Earth. It is a barred spiral galaxy and is located in the Local Group of galaxies.

Proxima Centauri is the closest star to the Earth. It is located in the constellation Centaurus and is part of the Alpha Centauri system.

Mercury is the planet that is closest to the Sun. It is a small, rocky planet with a thin atmosphere.

Mars is the planet that is known as the 'Red Planet'. It is a rocky planet with a thin atmosphere and a surface that is covered in craters and canyons.