From the Memoirs of Sr. Lucy of Fatima:

High up on the slope in the Cova da Iria, I was playing with Jacinta and Francisco at building a little stone wall around a clump of furze. Suddenly we saw what seemed to be a flash of lightning... We began to go down the slope, hurrying the sheep along towards the road. We were more or less half-way down the slope, and almost level with a large holmoak tree that stood there, when we saw another flash of lightning. We had only gone a few steps further when, there before us on a small holmoak, we beheld a Lady all dressed in white. She was more brilliant than the sun, and radiated a light more clear and intense than a crystal glass filled with sparkling water, when the rays of the burning sun shine through it. We stopped, astounded, before the Apparition. We were so close, just a few feet from her, that we were bathed in the light which surrounded her, or rather, which radiated from her. Then Our Lady spoke to us: “Do not be afraid. I will do you no harm... I have come to ask you to come here for six months in succession, on the 13th day, at this same hour. Later on, I will tell you who I am and what I want." ...As she pronounced these last words “...the grace of God will be your comfort”, Our Lady opened her hands for the first time, communicating to us a light so intense that, as it streamed from her hands, its rays penetrated our hearts and the innermost depths of our souls, making us see ourselves in God, Who was that light, more clearly than we see ourselves in the best of mirrors. Then, moved by an interior impulse that was also communicated to us, we fell on our knees, repeating in our hearts: “O most Holy Trinity, I adore You! My God, my God, I love You in the most Blessed Sacrament!” After a few moments, Our Lady spoke again: “Pray the Rosary every day, in order to obtain peace for the world, and the end of the war.” Then she began to rise serenely, going up towards the east, until she disappeared in the immensity of space. The light that surrounded her seemed to open up a path before her in the firmament, and for this reason we sometimes said that we saw heaven opening.
 

(Secretariado dos pastorinhos,I, 8th ed., Fatima, 2005, pg. 174-176)