On National Dance Day last year, the crowd at the Kennedy Center took its moves outside. (Margot Schulman)

The actress’s iPhone photos were her proof.

Backstage at a gala, Jenna Elfman pulled up the black-and-white images on her Instagram account. Nigel Lythgoe, the co-creator of the television show “So You Think You Can Dance,” admired the girl on the screen — a blonde leaping in the air, legs perfectly straight, toes pointed as only a ballerina can point them.

“That’s me,” Elfman told him.

And, like that, she secured her spot as a guest judge on the popular Fox competition show.

Now, the dancer-turned-actress has dusted off her dancing shoes for National Dance Day events at the Kennedy Center on Saturday.

“I’m in one of my happiest places when I’m dancing,” she says. “It’s like home base.”

Elfman and Dushaunt “Fik-Shun” Stegall, last year’s male winner of “So You Think You Can Dance,” will be leading dance routines (you can see them here ), and performers will include Axis Dance Company and dancers from the CityDance Conservatory.

One of the aims of National Dance Day, which also is hosting events in New York, Los Angeles and Las Vegas, is to promote dance while bringing together people of all ages and backgrounds.

“The beauty of National Dance Day is that it appeals to all ages and all audience types: Families, tweens, grandparents and everyone in between,” says Meg Booth, the Kennedy Center’s director of dance programming.

Elfman became involved in National Dance Day through her board position at the Dizzy Feet Foundation, a charitable organization founded in 2009 by Lythgoe and “SYTYCD” director Adam Shankman.

The foundation launched National Dance Day in 2010 with some valuable help from Del. Eleanor Holmes Norton (D-D.C.). Norton had approached Lythgoe about getting involved with dance in conjunction with her interest in combating obesity. She introduced a resolution in Congress to declare the last Saturday in July as National Dance Day across the country.

Although never a serious dancer, Norton, too, will be in the Kennedy Center’s Grand Foyer on Saturday, learning the routines from Elfman and Stegall.

“I grew up in Washington, D.C. It’s a dancin’ town,” she says. “I hear a little music and I’m up!”

Elfman plans to bring her 4- and 7-year-old sons, who, when they’re not acting like ninjas and cowboys, enjoy dancing as much as their mom.

“Everyone should come out,” Elfman says. “If you’ve never tried dancing before, you will experience joy in a way you’ve never experienced it.”

National Dance Day

Saturday from 5 to 7 p.m. in the Kennedy Center’s Grand Foyer, 2700 F St. NW. 202-467-4600. www.kennedy-center.org. The event is free and open to all skill levels. Participants are encouraged to arrive early and wear comfortable clothing and shoes.