For every visible star in the observable universe, there are nine masses that are invisible and unidentified. Learn more about the astronomer who proved the existence of dark matter.

Cosmos, Contact, Icarus and Billions and Billions—from TV and movies to professional journals and best-selling books, Carl Sagan's influence was legendary.

The idea of launching a telescope into orbit was first suggested in 1923, but the idea wasn't realized until nearly 70 years later. Along the way, there were several obstacles and setbacks.

Astronomer Fritz Zwicky was the first person to conceive of supernovas, neutron stars, dark matter, and gravitational lenses. So why don't more people know his name?

This Nobel Prize–winning chemist contributed to several scientific fields. His remarkable body of work spanned chemistry, geochemistry, lunar science, and astrochemistry.