He said he saw the phenomenon various times, considering it a confirmation of his plan to declare the dogma.
The papal note says that at 4 p.m. on Oct. 30, 1950, during his "habitual walk in the Vatican Gardens, reading and studying," having arrived to the statue of Our Lady of Lourdes, "toward the top of the hill [...] I was awestruck by a phenomenon that before now I had never seen."
"The sun, which was still quite high, looked like a pale, opaque sphere, entirely surrounded by a luminous circle," he recounted. And one could look at the sun, "without the slightest bother. There was a very light little cloud in front of it."
The Holy Father's note goes on to describe "the opaque sphere" that "moved outward slightly, either spinning, or moving from left to right and vice versa. But within the sphere, you could see marked movements with total clarity and without interruption."
Pius XII said he saw the same phenomenon "the 31st of October and Nov. 1, the day of the definition of the dogma of the Assumption, and then again Nov. 8, and after that, no more."
The Pope acknowledged that on other days at about the same hour, he tried to see if the phenomenon would be repeated, "but in vain -- I couldn't fix my gaze [on the sun] for even an instant; my eyes would be dazzled."
Pius XII spoke about the incident with a few cardinals and close collaborators, such that Sister Pascalina Lehnert, the nun in charge of the papal apartments, declared that "Pius XII was very convinced of the reality of the extraordinary phenomenon, which he had seen on four occasions."