Spend enough time on Capitol Hill, and chances are you'll run into your fair share of celebrities.
This afternoon, it was actress Mira Sorvino testifying before a House committee about Darfur, Sudan.
She didn't draw much of a crowd, though.
It was probably because she was the third celebrity to make an appearance here today.
Sorvino had to vie for attention with TV legend Mary Tyler Moore and singer-songwriter Jewel.
Call it the Angelina Jolie effect. These days, it seems nearly every star has a cause.
Whether it's rocker Bono pitching for debt relief in Africa or singer Harry Connick Jr. pitching in for hurricane relief in New Orleans, do-gooder celebrities can be spotted everywhere.
And no place is more popular than Capitol Hill -- where a minigalaxy of stars appeared today.
Experts say that for advocacy groups or charities hoping to get attention and money, a famous spokesperson can be priceless.
"The right celebrity who has credibility on a cause can do a lot," said Shawn Sachs, the executive vice president of Sunshine Consultants, an organization that represents celebrities like Leonardo DiCaprio and Justin Timberlake.
"There's a certain amount of attention that makes politicians listen to people like George Clooney."
But it can also be a mutually beneficial arrangement.
For celebrities, advocacy work can offer a new way to round out a career.
The causes today's stars represent run the gamut.
Kelly Clarkson came to the Hill earlier in the year to campaign against illegal downloading; Ben Affleck testified before a committee on "The Promise of the Genomic Revolution."
Sorvino, an Amnesty International representative, has been lobbying on Darfur for more than two years.
It's an issue she's been passionate about for even longer. She wrote her senior thesis at Harvard on genocide.
For some stars, the cause they adopt is even more personal.
Michael J. Fox, who suffers from Parkinson's disease, lobbied for stem-cell research earlier this summer.
So did Moore, who has diabetes and has become something of a regular on the Hill.
This morning she addressed a small group in the basement of the Capitol building.
But not all star advocates have a clear connection to their cause.
Though Jewel was on the Hill today to talk about breast cancer, neither she nor anyone in her family has had the disease.
"I believe as an artist I have the opportunity and a responsibility to use my voice to support a cause," she said.
While some stars are highly articulate, others recognize that what's really important is just showing up.
When Cher came to push for upgraded helmets for U.S. troops, she sat quietly at a hearing, but never spoke.
Still, whether testifying or providing a photo op, celebrities draw attention from the public -- and from Congress.
That's why they call it star power.