On this day in 1819 - June 5th - British mathematician and astronomer John Couch Adams was born.
His most famous achievement was predicting the existence and position of Neptune, using only mathematics. But Urbain LeVerrier had independently made the calculations and the planet was discovered using LeVerrier's calculations. (Who discovered Neptune?)
On this day in 1625 - June 8th - Italian-French astronomer Giovanni Domenico (Jean-Dominique) Cassini was born.
Cassini was one of the most important astronomers of the 17-18th centuries, and was the first of four Cassinis to direct the Paris Observatory. The NASA/ESA/ASI Cassini-Huygens mission to Saturn bore his name because of his study of Saturn, which included the discovery of four of Saturn's moons.
On this day in 1812 - June 9th - German astronomer Johann Gottfried Galle was born.
Galle is best known for his being the first person to see the planet Neptune, knowing what he was seeing. This followed his search for the planet using the calculations Urbain Le Verrier had sent him. (Who discovered Neptune?)