An artist's impression of the dwarf planet Pluto as it might appear from the surface of its biggest natural satellite, Charon. The New Horizons probe has revealed that Pluto is a ruddy red colour. In this depiction, Pluto's phase is new - i.e. the Sun is directly behind it. Therefore Pluto is only visible by the faint sunlight that Charon reflects onto it from the Sun. Because Pluto and Charon are tidally locked, they keep the same face towards each other at all times, as the Moon does to the Earth. So if one stood on Charon (or Pluto) the other world would stay fixed in the sky - never setting or rising, but still cycling through its phases. And if one were on the wrong hemisphere of Pluto (or Charon) one would never see the other world.