Ridiculous though it may seem, Stephen Colbert is testifying before congress this Fridayabout immigration reform . While not an expert on the subject, he did devote a day to working on a corn farm in an effort to raise awareness about United Farm Workers and undocumented immigrants. But it's not his expertise the savvy politicians behind his testimony are after, it's his celebrity.

It's not hard to understand the appeal: Celebrities, by virtue of being famous, are able to bring considerable attention to the causes they choose to represent, which is why they're often asked to come before congress and spread their tail feathers. Here are six examples of famous folks who went to Washington for a cause.

Nick Jonas, who was diagnosed with diabetes at age 13, testified in the U.S. Senate in 2009 about the need for addition research and testing for the ailment.


 

Unlike many famous people who testify before congress, Kevin Costner spoke as an entrepreneur and inventor first and a celebrity second. Since the Exxon Valdez oil spill in 1989, the actor has put tens of millions of dollars into Ocean Therapy Solutions, which has developed a technique for separating oil from water. In June of this year, he appeared before Congress to talk about technologies that could be used in mitigating future oil spills.
 

The musician and breast-cancer survivor Sheryl Crow came before congress in 2008 to support an act that would fund research on breast cancer.