Sun Clock at Kitt Peak National Observatory, Arizona 386, Sells, AZ 85634
N 31° 57.595 W 111° 35.886
12R E 443481 N 3536148
The polished sphere of Jacobs' sun clock.
Waymark Code: WMNYZV
Location: Arizona, United States
Date Posted: 05/26/2015
Views: 9
The polished sphere of Jacobs' sun clock forms an image of the sun that moves 15 degrees per hour, enabling it to tell time. (The sun appears to make one revolution around the Earth every 24 hours, or 15 degrees per hour.)
Jacobs said it took 15 years to overcome "many interesting technical problems" to develop the clock, which yielded an unexpected discovery about the optics of a sphere.
"As soon as the polished sphere was finished, we got a big surprise," he said. "I mounted it in my window, expecting to see an aberrated image of the sun, but in addition there were two white rings that no one could explain. Turns out the optics of a sphere were never studied so thoroughly before modern ray-tracing was available. The rings proved to be due to 5 and 9 complete round trips reflecting within the sphere."
Jacobs copublished a paper on the phenomenon in October 1997. ("Unusual Optical Effects of a Solid Glass Sphere," Jacobs, Stephen F. and Johnston, Steve C. Optics & Photonics News [OPN], pp 44-45 and 72, Vol. 8, No. 10)
"The optics of a glass sphere were thought to be pretty well understood by then," Jacobs said. "For example, in his wonderful book The Rainbow ( Sagamore Press, 1959), Carl Boyer discussed the position, breadth and color arrangement for each of the rainbows of the first 19 orders (spherical water drop). That's a lot of ray tracing! And yet no one could explain the observed white rings whose picture we published in OPN."
The sun clock was a team effort: Corning Glass Works donated the fused silica material about 20 years ago; Charles Amling, a glassblower at UA, created the glass focal surface; Greg Lowe, of Photon Dynamics Inc., in Tucson, made the special durable reflective surface; James Izlar Sr. and James Izlar Jr., of Izlar Industries, built the mountings; James Hunnicutt, of Tucson Spraying Technology, spray-painted the mounting; and Mike Woods, of Southern Arizona Sandblasting Services, sandblasted it. Steve Johnston, vice president of research and development at Photon Engineering LLC, of Tucson, provided an optical analysis of the unexpected on-axis double ring, and Roland Shack, professor emeritus at UA, provided "constant encouragement," Jacobs said.
For more information, visit: www.optics.arizona.edu
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