I wanted to know the books required for Astronomy Olympiad Senior Level

Hii

you can look upto this books for reference of your Astronomy Olympiad Senior Level


Textbooks of Physics and Mathematics by NCERT, upto Class X for Juniors
Textbooks of Physics and Mathematics by NCERT, upto Class XII for Seniors (calculus not necessary)
Fundamentals of Physics authored by Resnick and Halliday (The book is for basic astronomy. It is available in regional languages which the students can refer.).

Concepts of Physics by HC Verma (The book is for basic astronomy. It is available in regional languages which the students can refer.).
Universe written by Roger A Freedman and William J Kaufmann III The Physical

Universe by Frank Shu Astronomy: Principles and Practice penned by MN Roy and RC Clark (Stage II onwards) (Consider only those topics which have been taught till your high school level as certain topics have indepth and advanced knowledge.).

Astronomy: Structure of the Universe penned by the authors MN Roy and RC Clark (Stage II onwards) (Consider only those topics which have been taught till your high school level as certain topics have indepth and advanced knowledge.)

Astronomy for the Beginners written by Pradeep Nayak

Best of Luck