The Encore Westerns channel celebrates the 50th anniversary of “Gunsmoke” (5 p.m., Western) with a 50-episode marathon of the vintage series that will run all weekend, concluding Sunday evening.

“Gunsmoke” ran from 1955 to 1975, and starred James Arness as Marshal Matt Dillon, the lawman of Dodge City, Kan. Arness played Dillon for all 20 seasons, setting a longevity record for a television character only recently surpassed by Kelsey Grammer’s portrayal of Dr. Frasier Crane on both “Cheers” and “Frasier.” Amanda Blake, who played Miss Kitty, owner of the Long Branch Saloon, only lasted 19 seasons.

“Gunsmoke” proved so successful that it generated a glut of imitations during the late 1950s and early ’60s. At one point, there were 30 Westerns playing on the three major networks. And you thought the reality fad was out of control.

With the exception of “Bonanza,” “Gunsmoke” was the only Western to survive the changes in programming tastes, from quiz shows to escapist comedies, police and medical dramas, and socially relevant sitcoms. When “Gunsmoke” debuted in 1955, “The $64,000 Question” was the No. 1 show. When it finally left the airwaves, “All in the Family” held that position. But even after 20 seasons, “Gunsmoke” ranked in the top 30 in the Nielsen ratings. It ranked No. 2 as late as 1969-’70.

Other highlights

¢ Country singer Wynonna Judd appears on the first of two episodes of “Hope & Faith” (8 p.m. and 8:30 p.m., ABC), about the two sisters appearing in a “Wife Swap”-type reality show.

¢ Dolly Parton guest stars as a real estate agent on “Reba” (8 p.m., WB), starring fellow country-music superstar Reba McIntire.

¢ Scheduled on “60 Minutes II” (7 p.m., CBS): the AARP and Social Security reform.

¢ Scheduled on “Dateline” (7 p.m., NBC): an American soldier, declared missing and then dead during the Vietnam War, resurfaces decades later in New Zealand and answers questions about the American wife and family he left behind.

¢ The Washington Redskins play host to the Pittsburgh Steelers in NFL preseason action (7 p.m., Fox).

¢ Craig goes off his medication and loses control on “Degrassi: The Next Generation” (7 p.m., Noggin).

¢ Scheduled on “20/20” (9 p.m., ABC): Novelist Elizabeth Kostova travels to Transylvania to discuss her best-selling book “The Historian” (Little, Brown, 2005) and discuss vampire lore, fact and fiction.