Astrophysics is the science of physical processes in the cosmos. It uses data gathered by astronomers using telescopes on Earth and in space – combined with the laws and theories of physics – in order to interpret the universe around us. If astronomy asks what and where, astrophysics asks how and why. A sister science – planetary science – studies the planets in our solar system and distant solar systems in our Milky Way galaxy. Another sister science – cosmology – studies external galaxies and voids, and the large-scale structure and history of the universe.