Anyone interested in observing an eclipse should be familiar with radiometry and photometry. These topics are important for an understanding of illumination and exposure in photography. Photometry is also useful in astronomy to measure the magnitude of stars.
The history of the subject can be traced back to ancient times. Hero of Alexandria and Ptolemy both wrote books on optics. These works were essentially geometric in nature but Ptolemy touches on the idea of the cone of vision. Although ancient philosophy considered vision to be projective in nature, i.e., ideas projected onto objects, with visual rays "emanating" from the eye they recognized that light line of sight were essential for the visual process.
Here are some selected references which show the subject's developement over time,
1866 Emissive and Absorptive Power - Kirchhoff
1888 An elementary treatise on heat - Stewart
1914 Theory of Heat Radiation - Planck
1914 Standardization rules of the AIEE
1918 Radiation, light and illumination - Steinmetz
1920 Journal of the Optical Society of America
1950 Radiative transfer - Chandrasekhar
1998 Introduction to radiometry - Wolfe
2012 Applied Photometry, Radiometry and Measurements of Optical Losses - Bukshtab