Luna is light yellow, with green spots that resemble craters. Her eyes have yellow sclera with black pupils, eyelashes and eyebrows. She a long pink nose and flesh-colored arms and legs. She wears an Italian gondolier straw hat with a blue Chinese silk ribbon, and red boots. Her feet have three toes.
When she returns to the sky, her legs vanish, leaving nothing but her arms, body and face, though her face and arms eventually fade out as everything in her appearance simply disappears as well.
Luna is a bright bubbly moon who is a parent/teacher-like figure to Andy, Carmen, and Leo. She is patient, caring, and can get a bit silly at times. She is a friend to everyone on Earth and is held in an almost celebrity-like esteem by many when she appears.
She's also quite sensitive to the moods of others - if she's somewhere where a lot of people are sad or upset, she becomes sad as well.
Luna is the moon. She is always coming down to Earth at daytime to hang out with Andy, Carmen, and Leo to help them learn the places as they travel around the Earth, as the trio are part of a traveling circus that never stays in one place for a prolonged period of time.
During the trio's travels, Luna shows them around the locations they are currently residing in, telling them about the various cultures, landmarks, and people of the countries in particular. In some cases, she reveals some facts that most people wouldn't know about (such as the fact Big Ben refers to the great bell inside the clock tower and that the real name of the tower is Elizabeth Tower). This information is often times very helpful to them, and they use the knowledge to help them solve various personal problems. When night comes, she returns to the sky.
In "Where's Luna?" Luna is mysteriously absent, so the trio goes on a wild goose chase to find her. They eventually travel to a large set of Indian, astronomical tools in an attempt to find Luna more effectively. Eventually, Luna shows up and reveals that she was looking for her hat all along (which the trio had been carrying along the way), she apologizes that she wasn't able to take the trio on an adventure as usual, but they state that that wasn't the case, as the chase itself was an adventure after all.
She is one of the few characters on the show who is not an animal, and the only main character to fit that criterion.
She knows the names of everyone on Earth and may be over four billion years old.
All of China celebrates her existence during the Mid-Autumn Festival (also called The Moon Festival), as shown in "She is the Moon of Moons" and she makes a habit of appearing, in order to to honor the effort they put into honoring her.
In "Hoopin' Hopper", she appears to be capable of magic and she has used magic several times since, though she prefers to keep this particular ability hidden when in public: When repairing the damage Mathilda did to Franz's shop in "Glocken Around The Clock", she told him to not mention it. Literally.
When she is not in the sky, she almost always has something on her head: her standard hat, a helmet, or a hat befitting her environment.
She is strong enough to pick up both a giant Matryoshka Doll, and a giant statue (though in the second case, the statues were likely made of a light material such as papier-mâché) and was capable of throwing Jiro the Sumo wrestler a good distance in "You Can't Move the Moon". She also appears to be quite heavy: in "Aren't We A Pair?", the camel she was riding was clearly exhausted by carrying her, Jiro was unable to move her an inch during their match in "You Can't Move the Moon" and in Rhinoceros or Bust, the jeep she was riding in sank quite low on its springs when she got back into the drivers seat.
In "Spring Has Not Sprung", she appears to be allergic to colored powder, since it gave her nose a little tickle and made her sneeze.
In "Lizardzilla!", she appears to be a Lizardzilla fanatic, since she even bought a talking Lizardzilla plushie that tells the owner to give him a hug or he'll sit on you, and found the toy cute and started to blush and her eyes grew big and shiny as seen in famous anime TV shows and movies.
She doesn't always meet the entire trio at the same time. In "Totally Totem", she met with Andy and the two went on an adventure together before they joined Leo and Carmen.
Her size often poses a problem with doorways and particularly with enclosed spaces, as she has to literally squeeze herself into the area. This involves a good amount of uncomfortable struggling getting in and out.