The telescope was also instrumental in the discovery of dark energy, a little-known but ubiquitous force that works against gravity and contributes to the ongoing expansion of the universe.

It essentially made Hubble into a new telescope. "ACS has roughly ten times the discovery power of the previous camera," says Mario Livio, astronomer at the Space Telescope Science Institute in ...

In 1920, astronomers Harlow Shapley and Heber Curtis held a Great Debate. Shapley argued that the spiral nebulae were small ...