At the Institute for Astronomy last week, a high-tech snack was in the making.

Graduate students Kirsten Larson and Andy Mann were popping corn using a giant Fresnel lens to focus sunlight onto the kernels and make them explode.

The lens will be a star attraction at the Institute for Astronomy tomorrow when Larson and Mann hope to demonstrate more experiments — culinary and otherwise — at the annual Open House. "We want to show how powerful the sun is, and how cool optics is," Larson said.

A Fresnel lens is a series of circular prisms that focus light (one of the largest Fresnel lenses is in Makapu'u Lighthouse). After scavenging a 3- by 4-foot lens from an old projection television, Larson and Mann built a support frame enabling them to easily concentrate sunlight into a small surface area. The lens will be set up in the courtyard and they're hoping the sun will cooperate.

"That point of light is between 800 and 1,200 degrees Fahrenheit. It's hot enough to bend pennies," Mann said, pointing to melted coins on the ground nearby.

Can they fry eggs?

"We've tried grilled cheese sandwiches," he said. "They burned to a crisp in some places and were totally undercooked in others."

The Fresnel frying is part of a day packed with activities for children and adults, including comet making, bottle rockets, games and short lectures. A big Lego moon base will be on display, and telescopes will be set up in the courtyard to look for sunspots and the moon.

Astronomy projects from last week's state science fair will be on show, and, in the library, astronomers, including those working on the killer-asteroid hunting Pan-STARRS project, will be on hand to answer questions. Members of the Hawaiian Astronomical Society, the Bishop Museum Science Center, Ironwood Observatory and the Windward Community College Center for Aerospace Education will lend a hand.