Roy G. Biv Visits the Union Club

Rainbow on wall of the UA Student Union

A "Light Moment" prepared by Tammy Orr

In nature, rainbows occur when sunlight shines into water droplets in the atmosphere, bending as it moves from the air into the water, reflecting off the sides of the drops, and bending again as it exits the drops. So, in the absence of a skylight and an indoor rainstorm, how would you create a rainbow inside the UA Student Union? Hint: The collective ingenuity of an OSC professor, a graduate student and an optics technician.

One day in 1988, professor Steve Jacobs came across an advertisement for a curvy plastic prism. Always on the lookout for ways to introduce others to the beauty of optics, he decided this simple device would be a novel way to simulate a rainbow. And what better place to showcase his idea than over the salad bar at the Union Club where he and his colleagues frequently ate lunch?

Steve Jacobs and Jose Sasian work on the Student UnionThe curvy prism refracted sunlight from a nearby window onto the wall to produce the rainbow effect. However, as the sun swept across the sky, its light disappeared from the window, and the rainbow lost its glow. To compensate for the earth’s rotation, a sun-tracking mirror controlled by a stepper motor was used, making daily remote resetting of the mirror angle convenient and easy. To design and construct this novel optomechanical system with very inexpensive hardware, professor Jacobs enlisted the help of then-Ph.D. student Jose Sasián and optics technician Dan Bass.  

There were a few challenges to such a project. One of the biggest was placing the sun-tracker on the outside of the Student Union without creating a headline in the Daily Wildcat that read, “Optical Sciences Center Professor Recreates Scene from ‘Under the Rainbow.’” (The scene in question comes from the 1981 movie starring Chevy Chase, in which Rollo Sweet, played by Cork Hubbert, climbs to the roof of a barn to fix an antenna, then slips and falls to the ground.)

In two months’ time, Jacobs and his team successfully projected a rainbow on the wall that was bright enough to look impressive even in the lighted restaurant. It shone for over a year.