The people had gathered because three young shepherd children had predicted that at high noon the lady who had appeared to them several times would perform a great miracle in a field near Fátima called Cova da Iria. According to many witnesses, after a period of rain, the dark clouds broke and "the sun" appeared as an opaque, spinning disc in the sky.[4] It was said to be significantly duller than normal, and to cast multicolored lights across the landscape, the shadows on the landscape, the people, and the surrounding clouds. The sun was then reported to have careened towards the earth in a zigzag pattern,[4] frightening those who thought it a sign of the end of the world.[5] Witnesses reported that their previously wet clothes became "suddenly and completely dry, as well as the wet and muddy ground that had been previously soaked because of the rain that had been falling".[6]
Estimates of the number of people present range from between 30,000 to 40,000 by Avelino de Almeida, writing for the Portuguese newspaper O Século,[7] to 100,000, estimated by Dr. Joseph Garrett, professor of natural sciences at the University of Coimbra,[8] both of whom were present on that day.[9]
The event was attributed by believers to Our Lady of Fátima, a reported apparition of the Blessed Virgin Mary to the children who had made predictions of the event on 13 July 1917,[10] 19 August,[11] and 13 September.[12] The children stated that the Lady had promised them that she would on 13 October reveal her identity to them[13] and provide a miracle "so that all may believe."[14]