Astrophysics can be complicated with astronomical formulas to determine distance, speed, mass, gravity and much more. If you want to know how formulas were used to prove theories in astrophysics you can purchase: On the Shoulders of Giants: The Great Works of Physics and Astronomy edited and with commentary by the British theoretical physicist Stephen Hawking.
If you want an overview of space exploration that gives simple experiments to grasp the concepts without the formulas: An Earthing’s Guide To Outer Space by Bob McDonald is excellent!
Bob McDonald hosts CBC’s Quirks and Quarks
It’s an easy and good read that talks about how space travel came about, what it’s like to blast off in a rocket and live on a space station, and the effects living space has on the body. He also talks about planet movement, event horizons, and what the sun is made of. I’ve simplified what’s in the book so you can enjoy what I haven’t mentioned.