Luna is Earth's only moon, she is a sixth of her size, and she's 384.000km from her. Both her and Earth are very similar in personality, and they both love to investigate the universe, and always enjoy to spend time with other planets. She is tidally locked to Earth, so she always has the same part facing to her the whole time.
Personality
Luna is very similar to her mother Earth.She's always with a big grin, and loves to make other moons' days happier. She cares a lot for the moons of the Solar System, and loves to spend time talking with them. Her best friend is Callisto, as they are both very similar in personality as well. However, that doesn't mean that she doesn't like to spend time with Earth. They love each other a lot, and Luna and Earth spend most of their time together.
Appearance
Luna has two 'faces'. One of them is constantly facing to Earth. It's full of dark zones, or 'seas', and has some of her biggest craters there. The face that's never facing to Earth (also called 'the Dark Side') is just a bunch of impacts here and there, nothing else (besides some Apollo landers). You can also get wonderful views of Earth from her surface.