17 July

1894: On 17 July 1894, Georges Lemaître was born.

Lemaître was a Belgian astronomer and cosmologist, born in Charleroi, Belgium. He was also a civil engineer, army officer and ordained priest. In 1927, Lemaître was the first to propose the modern Big Bang theory. He said that if the Universe was expanding now, then the further back you go in the past, the Universe’s contents must have been closer together. He envisioned that at some point in the distant past, all the matter in the Universe was in an exceedingly dense state, crushed into a single object he called the 'primeval super-atom' which exploded, with all its constituent parts rushing away.

1850: On 17 July 1850, the Harvard Observatory in the United States took the first photograph of a star.

The observatory director, W.C. Bond and a Boston photographer J.A. Whipple took a daguerreotype of Vega.