On 9 December 1531, when Juan Diego was on his way to morning Mass to celebrate the Feast of the Immaculate Conception, the Blessed Mother appeared to him on Tepeyac Hill, the outskirts of what is now Mexico City. She asked him to go to the Bishop and to request in her name that a shrine be built at Tepeyac, where she promised to pour out her grace upon those who invoked her. The Bishop, who did not believe Juan Diego, asked for a sign to prove that the apparition was true. On 12 December, Juan Diego returned to Tepeyac. Here, the Blessed Mother told him to climb the hill and to pick the flowers that he would find in bloom. He obeyed, and although it was winter time, he found roses flowering. He gathered the flowers and took them to Our Lady who carefully placed them in his mantle and told him to take them to the Bishop as “proof”. When he opened his mantle, the flowers fell on the ground and there remained impressed, in place of the flowers, an image of the Blessed Mother, the apparition at Tepeyac.
A more detailed description can be found at https://www.catholiceducation.org/en/culture/catholic-contributions/saint-juan-diego-and-our-lady.html
The Catholic Church officially approved the apparitions of Our Lady of Guadalupe in 1555. Our Lady of Guadalupe was solemnly crowned Queen of the Mexican people in the name of Pope Leo XIII in 1895. Pope St. John Paul II declared Juan Diego beatified on the 6th of May 1990 and also canonised him on the 31st of July 2002.
The Miraculous Image of Our Lady of Guadalupe is rich in meaning. More recently, scientific analysis of the image on the cloak has verified its miraculous status including the reflection in Our Lady’s cornea of the bishop and 12 others present; the accurate topological map of Mexico on her dress and the constellation chart on her mantle accurate for 12th December 1531. And perhaps the most amazing recent discovery is that when the relative positions of the stars and motifs in the Image are analysed and superimposed upon sheet music they produce a musical score. This heavenly ‘music of the angels’ very closely resembles the singing of angels heard in Healing Masses. Perhaps it is also what Juan Diego heard that first day of the apparitions on Tepeyac Hill.
You can listen to this grace-filled music here http://www.youtube.com/watch?v=EU9lNCMWcTE or here