There was singing, dancing and bell ringing in Central Park for an artist who has lived long past the days when she was often vilified.At 90, Yoko Ono has outlasted her detractors, just as she more or less predicted she would in “Yes, I’m a Witch,” a defiant song she recorded in the 1970s.“I’m not gonna die for you,” Ms. Ono sang. “You might as well face the truth / I’m gonna stick around / For quite a while / Yes, I’m a witch.”To commemorate her 90th birthday on Saturday, more than 50 artists and fans gathered at the Naumburg Bandshell in Central Park to take part in “Morning Piece for Yoko Ono,” a 1960s-style art happening that doubled as a celebration.Many of those who showed up said they had become aware of Ms. Ono decades ago, around the time when she was newly married to John Lennon and the Beatles were breaking up.“I was a big Beatles fan when I was 10, 11, 12,” said the abstract painter Jean Foos, 69, “and I heard a lot of negative stuff about her. But once I came to New York and heard her music, I loved her.”The artist Jean Foos, right, posed for a photo with a Yoko Ono banner.Nina Westervelt for The New York TimesStaring at a black-and-white image of Ms. Ono printed onto a banner that hung from a wire on the bandshell stage, Ms. Foos mentioned “Season of Glass,” the album that Ms. Ono released in 1981, less than six months after Mr. Lennon was murdered.“For years in my studio, I would listen to ‘Season of Glass’ over and over,” Ms. Foos said, “especially while grieving different sad things that happened in my life. I just love her so much.”Carla Saad, a restaurateur who described herself as a “huge Beatles fan,” arrived with her 6-year-old son, Harrison Moscona. “I think Yoko is a wonderful artist,” Ms. Saad, 40, said. “She’s amazing, revolutionary, and I don’t think she’s given enough credit.”Her son, who was named after George Harrison, said, “I want to see Yoko — now!”Ms. Ono, who has not appeared in public in recent years, was not there. In 2019, at the Women’s March in Manhattan, she was photographed in a wheelchair. Two years before that, she mentioned that she was suffering from an illness, without specifying what it was. Representatives for Ms. Ono did not reply to emails seeking comment.Phillip Ward, left, and Jennifer Barton, the organizers of “Morning Piece for Yoko Ono.”Nina Westervelt for The New York TimesThe event on Saturday was conceived by the writer and curator Phillip Ward in the spirit of Ms. Ono’s conceptual art projects. He organized it with the public relations executive Jennifer Barton. In social media posts before the event, Mr. Ward and Ms. Barton asked participants to “say something nice about Yoko,” “bring your bells” and “make a wish.”A playlist of 39 tracks, including “Yes, I’m a Witch,” boomed out of the sound system as the celebrants gathered in the sunshine on a 32-degree morning. Around 10:30, the artist and activist Peter Cramer climbed onto the stage and grabbed the microphone, announcing, “I’ve got a song about Yoko. It’s called ‘She Thinks She’s Jackie Onassis.’”He danced and rang hand bells as he sang in a sharp falsetto voice: “Yoko! Oh, no! Oh, no! She thinks she’s Jackie Onassis!” A few people who appeared to be tourists stopped and stared at him. Moments after his brief performance, Mr. Cramer, 66, made it clear that he was a fan.“When I was a teenager,” he said, “I was in love with the Beatles — but I found that her music was much more in your face. I was getting into the whole punk scene, and it seemed a little more appropriate. It was aware of the troubles of the world in a way that appealed to my ear.”Peter Cramer, left, and Pascal Perich rang hand bells in honor of Yoko Ono.Nina Westervelt for The New York TimesAt a table near the stage, celebrants wrote messages to Ms. Ono on cardboard tags and picked up white carnations and button-size hand mirrors that said “Morning Piece for Yoko Ono” on one side. After the event, Mr. Ward and Ms. Barton delivered a white bag filled with the messages to the service entrance of the Dakota, the grand apartment house overlooking Central Park that has been Ms. Ono’s main residence since 1973.In his birthday message to the artist, Pascal Perich, a 51-year-old photographer, said he wrote “We are all dancing in the stars” in French, his native language. Asked to explain what he meant by that, he said, “It was just the first thing that came to my mind.”“I just love Yoko and Yoko’s work,” Mr. Perich continued. “She’s like the hummingbird that takes the little drop of water to the giant forest fire. And the animal tells him, ‘What you are doing is for nothing.’ And the hummingbird says, ‘No, I am just doing my part.’”The writer and musician Jesse Paris Smith, who is the daughter of the singer, songwriter and author Patti Smith and her late husband, the musician Fred “Sonic” Smith, also wrote a message. “I said, ‘Yoko is a true warrior of hope, peace and love for us all,’” Ms. Smith, 35, said. “When I think of her, I think of these wonderful universal truths. It might seem corny or cheesy, but it’s so deeply needed, and she embodies all of those things.”The artist Jack Waters, 68, said that “Grapefruit,” Ms. Ono’s 1964 collection of instructional poems, was a “seminal piece for me,” despite the fact that he didn’t really understand it when he first came across it as a teenager. “I think Yoko made her biggest impression on Beatles fans, but I grew up in a family where there was a lot of art and culture, so we knew her for her artwork,” he said.A pocket mirror that reads “Morning Piece for Yoko Ono” was given to fans.Nina Westervelt for The New York TimesPascal Perich wrote a note to Yoko Ono.Nina Westervelt for The New York TimesMany of the poems in “Grapefruit” ask readers to imagine different scenarios. In an interview with the BBC two days before his death, Mr. Lennon acknowledged that the book had directly inspired “the lyrics and the concept” of his 1971 ballad “Imagine” and expressed the regret that he had not properly acknowledged his wife’s contribution at the time. In 2017, the credits were formally changed to list Ms. Ono as the song’s co-writer.In recent years, she has gained new fans and greater respect among critics. The shift came partly as a result of “Yes Yoko Ono,” a retrospective that had its debut in 2000 at the Japan Society in New York before it moved to other cities. In The New York Times, Michael Kimmelman wrote that the exhibition revealed Ms. Ono to be “a mischievous, wry conceptual artist with a canny sensibility” who was “way ahead of her time in giving acute visual form to women’s issues.”Another wave of appreciation came with the 2021 release of Peter Jackson’s documentary series, “The Beatles: Get Back.” In his depiction of the group’s rehearsals, recording sessions and rooftop performance in January 1969, Ms. Ono made for a riveting presence.As the author Donald Brackett details in “Yoko Ono: An Artful Life,” a biography published last year, Ms. Ono was once the target of frequent misogynist and racist attacks in British and American publications. “It was horrifying,” Mr. Brackett said in a phone interview, describing the press accounts he came across during his research.John Lennon and Yoko Ono at the 1968 launch of “You Are Here,” their joint art exhibition at the Robert Fraser Gallery in London.Mirror Syndication International/Mirrorpix, via Getty ImagesMs. Ono stayed the same over the years, unwaveringly fierce in her art and mostly mild in her public statements. Little by little, many of the skeptics came around. “She once said, ‘You change the world by being yourself,’” Mr. Brackett said. “And she has undergone an evolution, maybe even a transformation, both as a pop culture figure and as a figure in the art world.”In March 1965, when the Beatles’ jaunty “Eight Days a Week” was the No. 1 song in the United States, Ms. Ono performed “Cut Piece” at the Carnegie Recital Hall in New York. She knelt on the stage, stoic, as audience members one by one cut off her clothing with fabric shears. That performance puzzled some of those who saw it at the time but is now considered groundbreaking. In “Yoko Ono’s Art of Defiance,” an essay published last year in The New Yorker, the cultural historian Louis Menand called “Cut Piece” “a truly great work of art.”Jennifer Barton, left, and Jesse Paris Smith sang Yoko Ono songs into the microphone as part of the 90th birthday celebration.Nina Westervelt for The New York TimesAs a child, Ms. Ono survived the Allied bombings of Tokyo, the city of her birth. That gave her something in common with Mr. Lennon, who was born during a lull in the Germans’ aerial attacks on Liverpool. Perhaps as a result of their common early experience, Ms. Ono and Mr. Lennon repeatedly explored the idea that the inner life is at least as important as the outside world. Mr. Lennon hit on this theme in the Beatles’ songs “Strawberry Fields Forever,” “Rain” and “There’s a Place,” and Ms. Ono seems to have made it a part of her art from the very beginning.“I remember, when we were evacuated during the war, my brother was really unhappy and depressed and really hungry, because we did not have very much food,” she said in a 2013 interview. “So I said, ‘OK, let’s make a menu together. What kind of dinner would you like?’ And, he said, ‘Ice cream.’ So I said, ‘Good, let’s imagine our ice-cream dinner.’ And we did, and he started to look happy. So I realized even then that just through imagining, we can be happy. So we had our conceptual dinner, and this is maybe my first piece of art.”Ms. Ono was among a pioneering group of artists who worked out of former factories and warehouses in Lower Manhattan. While living on Chambers Street in 1961, she came up with the conceptual art piece “Painting to Hammer a Nail,” which instructs the viewer to hammer nails into a canvas.The abstract painter Martha Edelheit, 91, was part of that scene. At the celebration on Saturday, she recalled her first encounter with Ms. Ono: “I walked in when she was doing an art exhibit — I think she was hammering nails into a wall.” Ms. Edelheit, who has a solo exhibition at the Eric Firestone Gallery in the East Village neighborhood of Manhattan through next month, added, “I’ve always loved what she’s done for the world as an artist.”The artists Ethan Shoshan and Martha Edelheit paid their respects to Ms. Ono on Saturday.Nina Westervelt for The New York TimesJim Fouratt, a gay rights activist and nightlife impresario, said he got to know Ms. Ono because of his role in the music world. At the Central Park happening, he recalled a time in the 1980s when she attended a show by the singer-songwriter Diamanda Galás at a club he ran, Danceteria.“Diamanda was never nervous about anybody,” Mr. Fouratt, 81, said. “But that night it took her 15 minutes to get on the stage because Yoko had planted herself right there. When it was over, and Yoko went backstage, all Diamanda could do was throw her arms around her, and she started to cry. It was a beautiful moment — that kind of recognition of a strong woman doing exactly what she wanted to do. That was the sisterhood between those two women.”In his message to Ms. Ono, Mr. Fouratt wrote: “Never look back. The adventure is the future.”The artists and fans in Central Park weren’t the only ones sending best wishes to Ms. Ono. Her son, Sean Ono Lennon, had set up a website, Wish Tree for Yoko Ono, that allowed people to send their messages online. By Monday afternoon, the site had collected more than 8,400 statements from her fans.It was not clear to people at the Saturday event if Ms. Ono was at the Dakota or at another one of her residences. “I don’t know if a lot of people know what’s going on with Yoko right now,” Mr. Fouratt said.Death was the theme of the Yoko Ono exhibition “Ex It,” which was installed last year at the Bank of Lithuania in Kaunas, Lithuania. The show comprised 100 wooden coffins of different sizes. In keeping with most of the artist’s other works, “Ex It” was hopeful: Each coffin had a fruit tree growing out of it.Ms. Edelheit, in the red hat, wrote a message to Ms. Ono at a table near the bandshell.Nina Westervelt for The New York Times More