The sky (or celestial dome) is everything that lies a certain distance above the surface of the Earth, including the atmosphere and outer space.
Hubble 20th Anniversary Photos: NASA Astronomers' Picks
For Hubble's 20th anniversary, NASA astronomers selected the pictures that best highlight the telescope's scientific and societal impacts.
The Science of 'Interstellar' Explained (Infographic)
Wormhole travel across the universe and supergiant black holes are just some of the wonders seen in the film 'Interstellar.' Here's how it works.