In 1920, astronomers Harlow Shapley and Heber Curtis held a Great Debate. Shapley argued that the spiral nebulae were small and in the Milky Way, while Curtis took a more radical position that they ...

A nebula is a giant cloud of dust and gas in space. Made mostly of hydrogen and helium, the nebulae (more than one nebula) are the space between the stars. Interestingly, this space is also known ...