“Degrassi Goes Hollywood” (7 p.m., The N) becomes the first movie-length outing for the Canadian high school series. But this “Degrassi” offering jettisons the usual topicality for a whimsical take on celebrity and its discontents.

The Canadian series always offered a more thoughtful and realistic alternative to its aggressively slick and gorgeous competition. And in this movie, the kids strive to strike it less-than-rich by auditioning for a project just this side of fabulous.

Director Kevin Smith guest stars as himself, as does his sidekick Jason Mewes, who appears here as the writer/director of “Mewesical High.” Look for cameos by Vivica A. Fox, Kelly Carlson and Cassadee Pope.

• The line between history and nostalgia can be a fine one. And on television, it’s often nonexistent. VH1 and the History Channel collaborated for the very first time on “Woodstock: Now & Then” (8 p.m., VH1), a clip-rich glance back at three days of fun and music that repeats on Monday at 7 p.m. on The History Channel.

Filmmaker Barbara Kopple mixes an impressive collection of interviews with archival footage of the 1969 concert’s preparation, presentation and aftermath. The film is best appreciated for the inside stories about the seat-of-the-pants planning for the festival between two shaggy music promoters and two young, rich Wall Street backers with money to burn (and burned it was) and their dreams of creating “Monterey Pop” east.

As you can imagine, there’s a lot more “Then” than “Now” to this film. Scenes of contemporary young people singing songs by The Who and Janis Joplin seem forced at best. A 10-year-old channeling The Who must realize that it’s not “My Generation” he’s singing about, but his father’s, or even his grandfather’s.

Several attendees expressed appreciation for the spirit of the times and wish it would return. But they seem to overlook the fact that events like Woodstock could never have happened in a popular culture burdened by an unhealthy obsession with the past.

It’s sobering, a little depressing, but ultimately eye-opening to note that now we are as far removed from the summer of Woodstock as 1969 was from 1929. I don’t seem to remember Jefferson Airplane performing tunes from “No, No Nanette.”

Besides some snap analysis that “it was a moment, not a movement,” there is little serious effort to put the event in the perspective of its times, or explain why Woodstock has remained a cultural touchstone, or why the Woodstock-Nostalgia-Complex has only grown more heavy-handed over the past 40 years.

• The long arm of the musical past also resurfaces on “Neil Diamond — Hot August Night: NYC” (7 p.m., CBS) featuring performances of “America,” “Cracklin Rosie,” “I Am…I Said,” “Cherry, Cherry” and “Sweet Caroline,” many of the same hits that he sang at the concert that inspired the “Hot August Night” album, released in 1972.

Tonight’s other highlights

• Jack and the team are taken hostage on the season finale of “Mental” (7 p.m., Fox).

• Clive Owen, Emily Blunt, David Attenborough and U2 appear on “Friday Night with Jonathan Ross” (7 p.m., BBC America).

• A guard dog’s overeating results in medical emergencies on “Dog Whisperer” (8 p.m., National Geographic).