For every astronomical topic that I have approached there has turned out to be a broader realm of possibilities than is commonly accepted or acknowledged. The "excursions" of this book are the examples. They mostly depart from the mainstream of conventional wisdom to offer a wider perspective with opportunities for further research. While my intent is to supplement that mainstream, the effect may appear to dismiss rather than to reconsider accepted tenets. Ample praise and credit for those accomplishments are already available in textbooks. Readers may very well disagree with some of the notions presented in these excursions, but I hope that they will pause long enough to evaluate the scientific basis for any disagreement. For the most part, these excursions remain incomplete and unfulfilled, yet they contain many ideas that are not available elsewhere. Whether these ideas are per­ ceived as a collection of unproven claims or as a storehouse of fresh opportunities will depend entirely on the attitude of the reader. The excursions do cover a rather wide span of disciplines, and that may lead to an unfocused overall impression. My hope is thereby to attract a broader audience than that of a single discipline, and to expose them to neighboring disciplines. The excursions all do have the common thread of optical science related to astronomy.