1) Foundations of Astrophysics by Barbara Ryden
2) Fundamental Astronomy by Karttunen et. al.
3) An Introduction to Modern Astrophysics by Bradley Carroll and Dale Ostlie
4) Astronomy Principles and Practice by Archie E. Roy and David Clarke
5) Introduction to Cosmology by Barbara Ryden
The following YouTube links are helpful resources. However, these are NOT curriculums with which the competitions are based on.
Introductory level: Astronomy and Space
Intermediate level: Crash Course Astronomy Series
Advanced level: Astronomy/Astrophysics