Surya Siddhanta is a book that tells us how to calculate time and space in the most accurate way possible. It was written a long time ago by some very smart people in India who wanted to figure out how things work in the universe.
Imagine you have a big clock that tells you what time it is, but this clock is different because it doesn't just tell you what time it is now, it can also tell you what time it will be in the future and what time it was in the past. This clock is super important because it helps us plan things like when to plant crops or when to have festivals.
The people who wrote Surya Siddhanta wanted to make an even better clock by understanding the movements of the sun, the moon, the stars, and the planets. They figured out that the Earth is always spinning and moving around the sun, and this movement causes day and night and the changing seasons.
They also found out that the moon moves around the Earth and affects the tides, and that the planets move around the sun in patterns that repeat over very long periods of time.
By studying all of these movements and patterns, the people who wrote Surya Siddhanta were able to create a very accurate calendar that could tell you what day it is and when special events will happen.
In summary, Surya Siddhanta is a book that tells us how to make a super accurate clock by understanding how the sun, moon, planets, and stars move. It's like a big puzzle that helps us understand how time and space work in our universe.