There are many good and helpful publications around. One such is “Astronomy”, which is a free and OpenStax resource.
This work is a textbook produced by the IAU and has been written to increase student access to high-quality learning materials, maintaining the highest standards of academic rigor at little to no cost.
Astronomy is written in clear nontechnical language, with the occasional touch of humor and a wide range of clarifying illustrations. This excellent textbook is made available free of charge in electronic form to students around the world. You can download this valuable text for free by visiting :-