What is the primary characteristic of the Moon?

The primary characteristic of the Moon is that it reflects sunlight at night. Unlike a star, which generates its own light through nuclear fusion, the Moon does not produce light. Instead, it acts as a mirror, reflecting sunlight that reaches it. This characteristic allows us to see the Moon shining brightly in the night sky.

In contrast, the other options do not accurately describe the Moon. It is not the largest planet, as that title belongs to Jupiter. The Moon also does not generate its own light, since any visible illumination is a result of reflected sunlight. Furthermore, the Moon has a very thin atmosphere, not a dense one, which does not support significant weather or air pressure like that found on Earth.