Reflections on Galileo and Early Optics

Web sites that might be of interest to students in
Prof. Phil Allen's Mystery of Matter course, PHY 313 / CEI 544

Compiled by John Noé,  Executive Director,
Stony Brook Laser Teaching Center.

The Galileo Project

The Galileo Project is a very extensive hypertext research resource on Galileo and the science of his time which is maintained at Rice University.

Chronological Histories

Chronological histories of optics from ancient times to the present may be found in A Brief History of Optics and An Anecdotal History of Optics from Aristophanes to Zernike.

Mathpages Essays

The web site contains a large number (literally hundreds!) of fascinating essays on topics in mathematics and physics, especially relativity. Most of the essays are rather technical, but a few of them relate more to historical issues in optics and have little or no mathematics. Galileo's Anagrams and the Moons of Mars concerns the early history of the telescope and what Galileo observed with his. De Mora Luminis  concerns Galileo, Roemer and the discovery that light travels at a finite speed. Finally, Stationary Paths discusses Snell's "law" about the refraction of light and Fermat's very elegant explanation for this with his "principal of least time."

Optics in Poetry

John Donne's 1633 poem The Ecstasy contains an interesting optical reference having to do with how vision was believed to work ("Our eye-beams twisted, and did thread // Our eyes upon one double string" [line 7]). The "pictures in our eyes" on line 11 is also an optical reference -- to the reduced image of oneself visible when looking closely at the eyes of another.

The Sun in the Church

The Sun in the Church is the title of a recent book by J.L. Heibron about the use of cathedrals for solar timekeeping at the time of Galileo. (The Church needed these observations to set the date for important events like Easter.) There is a description of the book as well as a detailed review at the Harvard University Press web site. Other reviews are available by William Broad from the New York Times and Paul Zweifel at Virginia Tech.

Pinhole Cameras

Various forms of the pinhole camera -- surely the simplest of optical instruments -- have great historical significance and considerable practical utility, even today. For example, there are hundreds of devoted photographic enthusiasts who prize the "soft look," wide field of view and nearly unlimited depth of focus of pinhole camera pictures as an art form, and tiny security cameras based on CCD light-detecting elements often simply use a pinhole for gathering the light. Pinhole devices are also convenient for safely viewing the intense light of the sun, as during a solar eclipse. Finally, pinhole cameras are easy to make, and have considerable pedagogical value. Follow the links in the next three sections to explore the world of pinhole optics!

Pinhole Photography

There are several comprehensive web sites with information on the history of pinhole cameras, pinhole photography, and making and using a pinhole camera. There's and the similar-sounding, which now reconnects to There's the highly alliterative Penultimate Pinhole Photography Page, and there's even a web site to celebrate the first Worldwide Pinhole Photography Day on 29 April 2001! Each of these web sites has lots of interesting and fun links to others.

Solar Cameras and Sunspots

Pinhole-type cameras provide a safe and convenient way to view the intense light of the sun, for example to observe an eclipse or "sunspots" (small dark areas on the surface of the sun). This was known in ancient times and remains a useful method. To get a reasonably large solar image one does have to arrange to have a distance of at least a few feet between the pinhole and the viewing screen. (This distance, in feet, divided by 9, gives the image diameter in inches.) On the other hand, because of the relatively large viewing distance the "pinhole" can be the diameter of a pencil or even larger.

A nice introduction to all this -- with links for further study -- is Could the Ancient Egyptians Have Observed Sunspots?
Or if you just want to learn how to make a pinhole-type solar projector try Another Look at the Sun. To learn more about the sun in general, visit the Sun Facts page prepared by Students for the Exploration and Development of Space at the University of Arizona. Last but not least, to learn more about what Galileo and contemporaries knew about sunspots try this page from the Galileo Project.

Camera Obscura

The term camera obscura (Latin for "dark room") originally meant a large pinhole camera for viewing an out-of-doors scene from inside a building or darkened enclosure. The term itself is said to have been coined by Kepler, but the idea for such devices is as old as Euclid (300 BC). Beginning already in the 1600's camera obscura rooms were created with lenses rather than a simple pinhole, and these evolved into our modern photographic camera.

There is a detailed and fascinating chronology of camera obscura devices at The Camera Obscura : Aristotle to Zahn by Dr. Russell Naughton. For information about camera obscura rooms of the type especially popular at sea side resorts and the like in the late 1800's see The Magic Mirror of Life by Jack and Beverly Wilgus. One of the devices described on the Magic Mirror site is a portable camera obscura constructed by John Serkin of Greenport (telephone 477-0744) and on display in his backyard at 306 Fourth St. John has proposed that a permanent device of this type by constructed on the Greenport harborfront, but the status of this endeavor is unclear. The Magic Mirror web site also has a link to interesting photos by Charles Schwartz from his camera obscura installation overlooking Central Park.

About the Laser Teaching Center

The Laser Teaching Center located in room S-202 of the Graduate Physics building is a new facility for individual student research projects in topics related to optics and lasers. Student researchers range from high school age or younger through graduate students. The LTC web pages provide news and information about the center's activities and various past, current and potential student projects. Teachers and others interested in learning more about the center are encouraged to contact Dr. Noé by email or telephone (631-632-4303) to learn more or to arrange a visit.