If you've been anywhere near the Flandrau Science Center and Planetarium in the last few weeks, maybe you have noticed its newest addition - a rainbow.

More precisely, it is corrugated steel sheeting covered with a plastic diffraction grating.

University optical sciences Professor Stephen Jacobs said he came up with the idea two years ago.

"I work with color and I thought it would be fun," he said. "It's purely a fun project."

The grating is composed of millions of small parallel cuts in the plastic and breaks the Tucson sunlight into its primary colors, Jacobs said.

Any engineering, astronomy, chemistry or physics student should be familiar with diffraction gratings, he said.

A much larger rainbow-maker of the same materials was installed on top of Tucson City Hall the weekend of Feb. 16. Jacobs' original goal was to encircle the top of City Hall with the reflective material, but fund-raising proved difficult, he said.

Private donations from donors such as Sun City raised half of the $25,000 needed to build and install the 50-by-10-foot piece on top of the 10-story City Hall, Jacobs said.

The rest of the money was matched by the Fluoresco Lighting-Sign Maintenance Corporation, he said.

City Hall's rainbow-maker reflects a bright rainbow although it is not even half the area Jacobs originally intended. Jacobs said the best times and locations to view the device are 2 p.m. from the freeway and 3:30 p.m. from Tucson Convention Center.

That is when the sun's angle is right for good colors, he said.

The sun will shine on the device at different angles as the months progress, Jacobs said, because of the earth's position relative to the sun. The angle determines which colors are showing, so as time passes the device will reflect different colors at the same time of day.

Jacobs said he has heard many reactions to the device's brightness, mostly from people who work in nearby offices.

"I understand some people are buying shades," Jacobs said.

Lisa Huston, business junior who works in the visitor's center across from the Flandrau Planetarium, said the smaller version is bright enough for her.

"It's kind of annoying but that's just because it gets right in my eyes," she said. "I was assuming it was some sort of a mirror."

Jacobs said his project has also drawn reactions from local artists who want to know where they can buy the diffraction material.

"You will see it (the material) in art around Tucson," he said.

Jacobs said Tucson's recent cloudy weather has kept his device from really shining yet.

Robert Moore, a production worker at the Student Union, said he had not noticed the rainbow-maker.

"I've been here twice a week and I haven't seen it," he said, as he waited at the bus stop across from Flandrau.