On a sunny Saturday morning when tween girls might otherwise be gearing up for soccer or glued to “iCarly” reruns on TV, they were calculating the speed of light and sporting safety goggles instead.

About 340 middle-school girls from throughout the Sacramento area gathered at California State University, Sacramento, for the “Expanding Your Horizons” conference.

The daylong program, in its fifth year at Sac State, is designed to motivate girls to take on careers in math and science.

The students took over classrooms in Sequoia Hall, learning how to build their own heart monitor, contemplating the size of the universe – and even using a microwave to blow stuff up.

“At this age, we see girls getting less interested in science,” said Sharon Puricelli, the conference’s program coordinator. “They don’t see a future in it, and think it’s all about wearing a lab coat. We have a one-day shot to make it exciting for them.”

Women have made large strides over the decades in earning science and engineering degrees. According to a study by the National Science Foundation, women in 1958 earned just 8 percent of all science and engineering degrees, but that number rose to 40 percent by 2006. Conference organizers hope it stays this way – or grows.

“When I majored in math and computer science at UC Davis in 1982, there were only three girls in the whole program,” said Michele Wong, president and CEO of Synergex International Corp., who addressed the conference as a keynote speaker. “I want to encourage women to get into science and technology careers. Twenty-six of the 34 fastest-growing career fields are in the sciences, and there will be a serious shortage if we don’t fill those fields.”

In one session, a group of about 30 students took over Room 418 at Sequoia Hall to learn about “microwave science.” Under the instruction of Cynthia Yuen, a Sac State chemistry professor decked in a tie-dye lab coat, they performed such experiments as “inflatable soap” and “group plasma.”

Placing grape halves in the microwave produced a lightning-like spark, since the shape of grapes acts like a mini-antenna and amplifies microwaves. (And please don’t try this at home, said Yuen.)

The middle-school attendees were also getting scouted early. A lunchtime career fair featured booths with representatives from UC Davis’ school of biotechnology, SMUD, the California Department of Transportation and others. But it sounded as if many of them just wanted to get back to the classroom and put their safety goggles back on.

“It was cool,” said Daisy Vang, a sixth-grade student at Rio Linda Preparatory Academy. “I like science and I like the experiments. I want to be a scientist.