Varahamihira was a renowned Indian astronomer and astrologer who lived in the 6th century CE. He is known for his work on astrology, including the Brihat Samhita, which is considered to be one of the most important texts on Indian astrology.

Astrology in ancient India was primarily used to predict the future, including events such as births, deaths, marriages, and the success or failure of various endeavors.

The Gregorian calendar is a modern calendar that was developed in Europe in the 16th century CE. It is not an ancient Indian calendar.

The Hindu solar calendar is an ancient Indian calendar that is based on the movement of the sun. It is also known as the Saka calendar or the Shaka Samvat.

The Hindu lunar calendar is an ancient Indian calendar that is based on the movement of the moon. It is also known as the Vikram Samvat.

The Hindu lunisolar calendar is an ancient Indian calendar that combines the solar and lunar calendars. It is also known as the Saka calendar or the Shaka Samvat.

Aryabhata was an ancient Indian astronomer and mathematician who lived in the 5th century CE. He is known for his work on astronomy and astrology, including the Surya Siddhanta, which is considered to be one of the most important texts on Indian astronomy.

The Jantar Mantar is an ancient Indian observatory that was built by Maharaja Jai Singh II in the 18th century. It is located in Jaipur, Rajasthan, India.

Varahamihira was an ancient Indian astronomer and astrologer who lived in the 6th century CE. He is known for his work on astronomy and astrology, including the Pancha Siddhantika, which is a treatise on five astronomical systems.

The astrolabe is an ancient Indian astronomical instrument that was used to measure the altitude of celestial bodies. It was also used for navigation and surveying.

Bhaskara II was an ancient Indian astronomer and mathematician who lived in the 12th century CE. He is known for his work on mathematics and astronomy, including the Lilavati, which is a treatise on mathematics and astronomy.

The sundial is an ancient Indian astronomical instrument that was used to measure the time of day. It is a simple device that consists of a stick or rod that is placed in the ground and casts a shadow.

Bhaskara II was an ancient Indian astronomer and mathematician who lived in the 12th century CE. He is known for his work on astronomy and mathematics, including the Siddhanta Shiromani, which is a treatise on astronomy and mathematics.

The quadrant is an ancient Indian astronomical instrument that was used to measure the distance between two celestial bodies. It is a simple device that consists of a quarter-circle of a circle with a plumb line attached to the center.

Mayur Bhatta was an ancient Indian astronomer and astrologer who lived in the 10th century CE. He is known for his work on astronomy and astrology, including the Surya Prajnapti, which is a treatise on astronomy and astrology.