This three-volume collection presents a unique set of original problems and solutions tailored to aspiring astronomers and astrophysicists participating in Olympiads and other competitions. The problems included cover a broad spectrum of relevant topics in astronomy and astrophysics, carefully curated by an author with extensive experience crafting problems for national and international Olympiad competitions. These books are designed to inspire critical thinking and sharpen problem-solving skills, enriching students' understanding and enjoyment of physics beyond the standard school curriculum. Each problem is accompanied by helpful diagrams and detailed solutions, providing readers with clear insights into the underlying physics and mathematical reasoning.Ideal for students, teachers, and mentors preparing for national and international competitions, these books are an indispensable resource for those eager to delve deeper into the wonders of the universe. Whether used for independent study or as a teaching aid, this series offers both intellectual stimulation and practical guidance. This third volume concludes the series with 45 original problems and solutions to challenge and engage the reader.