This book offers a perfect combination of classical optics and its use in understanding observable phenomena in nature and our surroundings. The science topics of the first part are those typically covered in undergraduate courses on optics. The author gives clear and concise introductions to geometrical optics, wave optics, detectors, and light sources. He also addresses radiometry, photometry, colorimetry, as well as quantum optics of light-matter interactions. End of chapter exercises help readers to test and consolidate their knowledge. In the second part of the book, a vast number of applications are presented both qualitatively and quantitatively. They include everyday atmospheric optical phenomena such as rainbows, halos, coronas, glories, mirages, sky colors etc., but also the colors of water, green flashes, the question how far we are able to see and many others. Stunning images of many natural optical phenomena will add greatly to the reader’s enjoyment of this book. The English translation of this book, originally in German, was facilitated by artificial intelligence. The content was later completely revised by the author for accuracy.