On June 29, 1900, a significant event in the history of physics took place. The renowned physicist and Nobel laureate Antoine Henri Becquerel discovered the phenomenon of radioactivity on this day.

Becquerel was born into a family of scientists and was already a well-established physicist by the time of his groundbreaking discovery. He was particularly interested in phosphorescence, a phenomenon where certain materials glow in the dark after being exposed to light.

One day, Becquerel was experimenting with uranium salts, which he knew were phosphorescent. He wrapped a photographic plate in black paper and placed a uranium salt sample on top of it. His intention was to expose the setup to sunlight and see if the uranium would create an image on the plate due to its phosphorescence.

However, the weather in Paris was overcast for a few days, so Becquerel stored the setup in a drawer. When he finally developed the photographic plate, to his surprise, he found that the plate had been exposed despite not being subjected to sunlight. This led him to conclude that the uranium salt was emitting a new type of radiation, which could penetrate the black paper and expose the photographic plate.

Becquerel had accidentally discovered radioactivity, a term later coined by Marie and Pierre Curie, who were inspired by his work. This discovery laid the foundation for the field of nuclear physics and had far-reaching consequences in various domains, including medicine, energy production, and even warfare.

Today, we celebrate Becquerel's serendipitous discovery on June 29, which forever changed our understanding of the atomic world and paved the way for numerous scientific and technological advancements in the 20th century and beyond. His work is a testament to the power of scientific curiosity and the importance of paying attention to unexpected results in the pursuit of knowledge.