It’s a new day up on the roof of New York’s Metropolitan Museum, above the clouds of cherry blossom in Central Park, over the gothic chapels, mummies and ancient coins. There, Big Bird dangles and bobs on a giant mobile, as if lulling a monster-child into a nap. Sunshine brings out harmonies of colour. The bird’s azure plumage merges with the sky and hums along with the pink, red, and purple tulips down below. Just you try not to smile.

What is a Sesame Street character doing at the Met? The answer rests with Alex Da Corte, whose whimsical sculpture “As Long as the Sun Lasts” comes wrapped in rarefied cultural sources. Charm may get you in the door of a great museum, but a roof garden commission implies a more, well, elevated purpose.

Big Bird perches on a sliver of moon and drifts in the breeze, counterbalanced by a constellation of metal discs. The whole composition rests on a fire engine-red fulcrum made up of three triangular steel blocks pitched into pyramidal form. It’s bright and big and 26 feet tall, a toy that takes its place on the skyline along with the jagged parade of towers at the southern edge of Central Park. Maybe that’s where he’s headed, with the ladder he clutches in one claw. Or perhaps he yearns for the heavens, but, confined to the city’s metallic grid, he can only dance and twirl for our pleasure.

Those dampened dreams may account for the air of melancholy surrounding the pinioned creature, whose 7,000 aluminium feathers are all blue instead of regulation yellow. For anyone who grew up counting and spelling with Elmo, Oscar and the rest of the crew, the change in hue is both startling and sneaky. Like a new haircut, it takes a moment to trigger the double-take.

As a child in Venezuela, Da Corte watched the Brazilian version of the show, in which Big Bird’s relatively scrawny counterpart, Garibaldo, wears shiny aqua. But blue-ness also has resonant emotional overtones in the English-speaking world. In the small catalogue that accompanies this one-work show, curator Shanay Jhaveri quotes James Baldwin: “The acceptance of this anguish one finds in the blues, and the expression of it, creates also, however this may sound, a kind of joy. Now joy is a true state, it is a reality; it has nothing to do with what most people have in mind when they talk of happiness, which is not a real state and does not really exist.”

Now, getting from Big Bird to Baldwin is a bit of a stretch (although the author of Go Tell it on the Mountain did also write a children’s book, Little Man Little Man). But the sculpture rings so many familiar bells that it sets off a clangour of associations. As Google and your local greetings card stand can attest, our collective visual library is cluttered with images of figures sitting on a crescent moon: angels, kids, cats, lovers, the fishing boy in the DreamWorks logo. Da Corte cites the cover of the 1976 album Four Seasons of Love, which has Donna Summer reclining in leggy lunar splendour.

Artist and curator are just getting going in the references department. Da Corte went snuffling about the Met’s holdings for inspiration and found it in another fantastical creature destined to whirl in circles — the protagonist of the medieval Unicorn Tapestries. In “The Unicorn Rests in the Garden”, the solitary beast lies in a lovely enclosure, secured by a slender tether and a low fence, mulling whether to spring free. “Da Corte envisions that his Bird will have to face a similar decision,” Jhaveri elaborates. “Removed from Earth, the character holds on to a ladder: is this a means of escape from a collapsed planet, a way to continue exploring elsewhere, or an affirmation to return to Earth? Does Big Bird want to leave this world behind?”

Not content with the notion of an oversized puppet reaching escape velocity or getting ready to end it all, Jhaveri invokes another famous emblem of romantic gloom, Caspar David Friedrich’s “Wanderer above the Sea of Fog”. Just as Big (is it OK if I call him Big?) contemplates his place in the universe from his jiggly perch, Friedrich’s loner surveys the craggy mountain tops from his foothold in the sky.

What doubts haunt our rooftop adventurer, that poetic soul of public television, that incarnation of the avian sublime? The genius of Sesame Street has always been in the way it treats tough topics — race, fear, anger — in ways that kids can handle, and that skill is in demand just now. The mournful Muppet overlooks a city that is finally emerging from terrible loss. Even now, those soaring office towers in the distance lie vacant and entire blocks are shorn of shops. Da Corte mustered his ideas for the Met commission during months of loneliness and uncertainty. He sought solace in two icons of good cheer: Big Bird and Alexander Calder.

For all the detours into Baldwin, unicorns and Friedrich, the great American sculptor, known for his kinetics, is Da Corte’s obvious touchstone. Just as Piet Mondrian was Calder’s. In 1930, Calder visited the Dutch artist’s studio in Paris and was thunderstruck. “This single visit gave me a shock that started things,” he remembered. “Though I had heard the word ‘modern’ before, I did not consciously know or feel the term ‘abstract’.” Having received the gospel of abstraction, Calder tweaked Mondrian’s severity with kinetic inventiveness, making balls rotate and miniature planets glide along orbital paths. Giddy from his breakthrough, he produced so many of these delicately balanced gizmos that they prompted Marcel Duchamp to coin the name for a whole new genre: mobiles.

It’s hard to recapture that sense of revelation now. Calder’s work has become such a ubiquitous presence that meeting the Met’s new commission feels like bumping into an old friend. That’s the power and the limitation of this rooftop sculpture, which is closely modelled on Calder’s “Gallows and Lollipops” in New Haven’s Beinecke Plaza. Maybe in the end all those philosophical musings and art-historical invocations are there to ornament the comforting memory of Da Corte’s undergraduate years at Yale.

To October 31,