Planetary Science

Pluto has five known moons:

1. Charon, the largest one, Charon was discovered in 1978.
2. Hydra, very small
3. Nix, very small, and two more-newly discovered small moons. and Nix/Hydra were identified in 2005.
4. Kerberos (provisionally named P4 or S/2011-134340)
5. Styx (S/2012-134340). On July 11, 2012, it was announced that a team of astronomers, using NASA's Hubble Space Telescope, discovered a fifth moon orbiting Pluto. The moon is provisionally designated as S/2012 (134340) 1. The moon was discovered by astronomers using nine sets of images taken by the Wide Field Camera 3 fitted to the Hubble Telescope between June 26, 2012 and July 9, 2012. It is estimated to be an irregular shape and 6 to 15 miles across.

The largest moon, Charon, is proportionally larger compared to its primary than any other satellite of a known planet or dwarf planet in the solar system. In fact there is some discussion as to whether we should consider this a "binary system" instead of a dwarf planet with moons because Charon is so massive that the barycenter (center of gravity around which the bodies rotate) of the Pluto-Charon group is not inside either of those bodies.

Jupiter Neptune

The planet that most extrasolar planets resembles Jupiter.

Jupiter(apex)
Most of the confirmed Exoplanets are larger gaseous planets with large masses. These are easier to detect and confirm due to their size. They most resemble Jupiter, although many are thought to be much larger than our largest planet.

The side of the moon that we can never see from Earth is often called the "dark side" (a) because it sounds cool, and (b) because darkness is a powerful metaphor for the unknown. In fact, the so-called dark side of the moon is not really dark. Luna has day and night on every part of its surface (just like Earth, only Lunar days are 28 Earth days long). During a new moon, for instance, the "dark side" is flooded with light.

The far side of the moon is dark in the metaphorical sense, in that we never see it. To people who think visually (most of us), lack of information seems like darkness.

How is it that there's a part of the moon we never see? Like many moons of planets in our solar system, our moon, Luna, keeps one side to its primary continually (there's a little wobble, so we can really see about 55% of the lunar surface). The moon is "tide locked" (read about tidal locking on wikipedia). This situation develops with all moons and planets over a long time. The Earth's rotation is slowing, too, and will eventually become tide locked to the sun (not for a very, very, very long time, but scientists can measure the tiny lengthening of the day).

Quibble: to be fair, the far side of the moon does receive less light than the rest of the moon, because it doesn't see any of the sunlight reflected from the earth. So technically, it is a bit darker overall. But nearly nobody who uses the phrase "dark side of the moon" is thinking of it in this way.