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On this day in 1951 – May 26 – Sally Ride was born.

Doctor Ride, astrophysicist, educator and astronaut, was the first American woman in space.

On this day in 1919 – May 29 – Einstein's Theory of General Relativity was tested during a total solar eclipse.

Under the direction of English astrophysicist Arthur Eddington, two groups of British astronomers observed the total eclipse. They photographed the positions of stars that appeared near the Sun. Then the positions of these stars were compared to a photograph taken when these stars were opposite the Sun. Einstein's theory predicted that the starlight would be bent by the Sun in the eclipse images. This is what the astronomers found in "Einstein's eclipse".

On this day in 1934 – May 30 – Alexei Leonov was born.

Cosmonaut Alexei Leonov was the first person ever to exit an orbiting spacecraft - the first "spacewalk". It nearly cost him his life, but he managed to get back into the craft and lived to make a second trip into space. He's also a talented artist.

On this day in 2003 – June 2 – ESA's Mars Express mission was launched.

Mars Express was the European Space Agency's first planetary mission. As of June 2016 the orbiter is still collecting and transmitting data.

On this day in 1948 – June 3 – the Hale 200-inch telescope was dedicated.

What was then the biggest telescope in the world was located at Palomar Observatory in southern California. It was named for George Ellery Hale who had persevered in the building of a telescope that was deemed to be impossible.

On this day in 1819 – June 5 – John Couch Adams was born.

Adams was a prominent British astronomer, best known for his prediction of the position of Neptune, independently of that of Urbain LeVerrier.

On this day in 1625 – June 8 – Giovanni Domenico Cassini was born.

Cassini (also known as Jean Dominique) was director of the Paris Observatory. Among his many accomplishments, he was known for his observations of Saturn. NASA's Cassini mission to the Saturnian system is named for him.

On this day in 2003 – June 10 – NASA's Martian rover Spirit was launched.

The mission was expected to last three Martian months, but lasted several years. In 2009 Spirit became trapped and was last heard from in March 2010. After a year of trying to make contact, on May 24, 2011 NASA formally ended Spirit's mission.

On this day in 1963 – June 16 – Soviet cosmonaut Valentina Tereshkova in Vostok 6 became the first woman in space.

Tereshkova is still the only woman to have flown a solo space mission.