Access to eBooks is limited to institutions that have purchased
or currently subscribe to the SPIE eBooks program. eBooks are not
available via an individual subscription. SPIE books (print and
digital) may be purchased individually on
Contact your librarian to recommend SPIE eBooks for your organization.
Shadows might seem like a trivial optical phenomenon, but they actually contain a variety of brightness and color if you observe carefully. This chapter focuses on the primary visual features that make watching shadows both entertaining and informative.
To begin, a shadow is a region of space devoid of direct illumination. However, the sun is not a point source but has an angular width near 0.5°, so it casts a dark shadow (the umbra) surrounded by a partially illuminated shadow (the penumbra). An exciting example is a solar eclipse (Fig. 6.1), in which the shadow of the moon blocks direct sunlight from reaching the earth.
Online access to SPIE eBooks is limited to subscribing institutions.