There’s a scene in Woody Allen’s “The Purple Rose of Cairo” that truly defines what musicals mean to me. In the film, 1980s-era Mia Farrow (“Be Kind Rewind”) plays a waitress from the Great Depression saddled with an abusive husband and no money. After a particularly exhausting day, Farrow approaches an empty movie house where “Top Hat” is playing. Distraught, she droops into her seat like a rag doll. The lights dim while Fred Astaire's "Cheek to Cheek" begins to descend upon her. Slowly, Farrow’s previously forlorn face breaks into a smile, her troubles temporarily forgotten. Such is the transformative quality of musicals.

In honor of its American Musicals series, the Michigan Theater has been showing a new musical from the golden heyday of Hollywood every Monday night for the past couple of months. I finally got around to seeing one: “It’s Always Fair Weather,” featuring Gene Kelly and the gazelle-legged Cyd Charisse.

The story — about three soldiers reuniting after 10 years of separation — is pretty humdrum, but the high energy of the stars more than makes up for it. Kelly jubilantly taps away on roller skates and gracefully swings Cyd Charisse around in a balletic arc. It seems like they are going to fall or mess up at any moment, but they always catch themselves with a cheeky smile to the camera.

I had seen this movie a couple years ago on DVD, but in the dark, with faces magnified 50 times over, it really is a magical experience. I felt like Mia Farrow in the midst of the Great Depression, and I just couldn’t keep my face from smiling.

Yes, I admit it; I’m a musicals junkie. “Singin’ in the Rain” is pretty much my favorite movie in the world. I have memorized all the dialogue. I know all the songs by heart. If I possessed any sense of rhythm, I would probably attempt to learn the dances too. I can’t help it; each time Gene Kelly, Debbie Reynolds and Donald O’Connor march up to the screen in matching yellow raincoats, it just gets me.

Musicals were once written to combat the Great Depression as a mode of escapism for those afflicted in the terrible times. It’s very difficult to describe a musical without making it sound completely stupid: The story is some kind of girl-meets-boy-hates-boy-loves-boy derivative, and the songs are grabbed out of a mix bag of reused and rejected material. But the greatest aspects about a musical are the ones you can’t describe: the effortless charm, the insane dance moves, the unfaltering optimism. For a star, a musical is truly one of the greatest mechanisms to do what he or she does best, which is simply to perform.

Fred Astaire, Frank Sinatra, Gene Kelly — these are movie stars to the highest degree, with enough personality and charisma to last a lifetime. The way they move, you’d think puppeteers were controlling their legs — it’s just so utterly perfect. The way they smile, their eyes wander directly to the camera as if they’re smiling just for you. Hamming it up for the screen becomes a positive thing.

These men have honed the art of entertainment like Michelangelo perfected his sculptures. The combination of it all — the resonant orchestra in the background, the exuberant energy of the songs, the sheer electricity of the dance sequences — it’s like they can’t close the curtains fast enough to make way for another dazzling musical number.

There really is no modern day equivalent of this enchanting film form. Today, musicals like the upcoming “Nine” are almost always large-scale productions adapted from the Broadway stage versions. The chorus is humongous — each dance sequence somehow needs to involve hundreds of extras — and the way the characters speak is very stagey. While I can’t deny that I enjoy these musical spectacles, I can’t help but feel that it is merely a good imitation of the real thing.

The death of the Hollywood musical is inextricably tied to the death of the classic Hollywood celebrity.