C-SPAN will celebrate 30 years of television in the House chamber Thursday.

The cable networks launched C-SPAN on March 19, 1979, as a public service to provide Americans with an up-close look at what their elected officials are doing in Washington, D.C. (Fun fact: Tennessee Democratic Rep. Al Gore was first to speak live on the House floor.) C-SPAN 2 went live on June 2, 1986.

The landmark gives Congressional insiders across the country a chance to think about how Congress has changed since 1979.

The network’s influence has grown over time, according to a Hart Research survey released in connection with the 30th anniversary.

For example, Hart found that “20 percent of cable TV households, an estimated 39 million Americans, watch C-SPAN regularly — at least once or twice a week,— according to a press release.

The survey shows that C-SPAN viewers use the information to get involved. Ninety percent vote, and high percentages work or volunteer on political campaigns.

Some of them use the information to get involved specifically with the network: 7,439 callers have had their say on the morning show “Washington Journal,— asking pointed questions and taking commentators to task. A segment of “Washington Journal— will be dedicated to the anniversary on Thursday.