I kid you not: Just as the tribe of beautiful performers dressed as hippies began to sing “Let the Sunshine In” during the opening night performance of “Hair” at the Delacorte Theater in Central Park, it began to rain ferociously.

While audience members popped their umbrellas, the cast members seemed to revel in the downpour during this, their climatic moment in an evening of memorable moments. It was an intoxicating rain dance and the line between artifice and reality just slipped away; an unforgettable ending to a wildly energetic and stirring revival of the great 1960’s tribal rock musical.

But that’s not all. Moments later, hundreds of people from the audience joined the cast on stage and danced uproariously for the length of the informal curtain call.

A ravishing and crowded mesh of New Yorkers up on the stage in the rain dancing to the music of “Hair.” That was an unforgettable moment for me and it was indicative of the way this production captures the imagination of a new generation of theater-goers, as well as boomers like myself who wore out their copy of the Hair album (and can sing along with every song but I didn’t).

My friend Anna Becker, producer of Life in a Marital Institution, James Braly’s virtuosic monologue at the Soho Playhouse, who took me to opening night, actually saw Hair as a 7-year old during its original run at the Public Theater.

It was hard not to be enthralled with the overall emotion of the evening.”Hair” is truly a classic show with a pantheon of great songs. The first act alone is is a veritable hit parade: Aquarius, Donna, Sodomy, Manchester, England, Air, I Got Life, Initials, Hair, My Conviction, Easy to Be Hard, Frank Mills, Hare Krishna and Where Do I Go.

The second act is darker and more narrative in a way. Much of it is a long hallucination about Vietnam and it contains some of my favorites like Walking in Space, Three-Five-Zero_Zero, The Flesh Failures, Let the Sunshine In and the transcendent What a Piece of Work is Man (lyrics by Shakespeare).

As someone who knows the score backwards and forwards, I will admit to some disappointments. Easy To Be Hard and Good Morning Starshine were totally lackluster. Frank Mills was slightly better. Overall the cast numbers were the best. Tony nominated Jonathan Groff from Spring Awakening gave a great performances, as did Will Swenson as Berger and Bryce Ryness as Woof. Patina Renea Miller, who sang Aquarius and other great numbers, also deserves special mention.

The show’s dramatic ark goes from euphoric hippydom to the darker realities. The song “Where Do I Go” perfectly encapsulates the feeling of the show in the second act: you can drop out but you can’t really escape what’s to come. In addition to growing up, the harsher realities of the world awaits these beautiful flower children.

This production of “Hair” is a history play that expertly transports the audience to the collective joy of the 1960’s without hiding the darker elements of war, drugs, sex without love, sexism, and aging.

The future awaits. And we all know that show.