Astronomy is a fascinating science. At the dawn of humanity, the human being looked up to the starry sky, looking for supernatural explanations for everyday phenomena. Today, with very sophisticated observation instruments, the harmony of the spheres keeps on disturbing us. But the apparent celestial harmony hides a violent universe, with gigantic explosions, thermonuclear reactions and extreme temperatures. This book is a general guide for the amateur astronomer, for lovers of Astronomy and even for the completely ignorant of the subject who wants to know the ins and outs of theoretical astronomy. This volume is divided into these sections: 1. Introduction. 2. Distances and coordinates. 3. The Earth-Moon-Sun system. 4. Celestial mechanics. 5. Observation of the sky. 6. The Solar System and the Milky Way. 7. Celestial objects. 8. Astronomical phenomena. 9. Space exploration. 10. Cosmology. It contains more than 270 spectacular images (photographs and drawings) that, in addition to complementing the explanation, have an undeniable aesthetic function.