I am a researcher and wish to learn astrophysics(research in dark matter). I have never studied astrophysics or astronomy. I am in search for a book that can guide me (1)How do astronomers predict masses of stars, galaxies and planets, their positions and relative velocities? (2) Also exercises and examples? Kindly provide me names, which can guide me on this. I am already studying a book "Fundamentals of Astronomy".