At Lake Tahoe, most people have heard the word “Secchi” in reference to the Secchi disk, a 10-inch white disk used to measure lake clarity. The Secchi disk remains the standard design used in both marine and deep-freshwater investigations because it is an inexpensive and straightforward method of measuring water clarity.

However, there is much more to the invention and the inventor. Join Brother Guy Consolmagno, American research astronomer, physicist, religious brother, director of the Vatican Observatory, and President of the Vatican Observatory Foundation, to discover the story behind inventor Angelo Secchi.

Angelo Secchi was a pioneer in astronomical spectroscopy and was one of the first scientists to state authoritatively that the Sun is a star. He invented the heliospectrograph, star spectrograph, and telespectroscope. He showed that certain absorption lines in the spectrum of the Sun were caused by absorption in the Earth’s atmosphere. He developed the first system of stellar classification, which is fundamental to the study of astrophysics. His recognition of molecular bands of carbon radicals in the spectra of some stars made him the discoverer of carbon stars. In addition to astronomy, Secchi was active in oceanography, meteorology, and physics.