The Moon is Earth's only proper natural satellite. At one-quarter the diameter of Earth, it is the largest natural satellite in the Solar System relative to the size of its planet, and the fifth largest satellite in the Solar System overall (larger than any dwarf planet). Orbiting Earth at an average lunar distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter, its gravitational influence is the main driver of Earth's tides and slightly lengthens Earth's day. The brightest and largest object in our night sky, the Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate. It also causes tides, creating a rhythm that has guided humans for thousands of years. The Moon was likely formed after a Mars-sized body collided with Earth. Earth's Moon is the fifth largest of the 190+ moons orbiting planets in our solar system.
Internal Structure: The Moon is a differentiated body. It has a geochemically distinct crust, mantle, and core. The Moon has a solid iron-rich inner core with a radius possibly as small as 240 kilometres (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometres (190 mi). Around the core is a partially molten boundary layer with a radius of about 500 kilometres (310 mi).
Surface: The Moon's surface is covered with dead volcanoes, impact craters, and lava flows, some visible to the unaided stargazer. The Moon's distance from Earth is about 240,000 miles (385,000km). The Moon has a very thin atmosphere called an exosphere. The Moon's entire surface is cratered and pitted from impacts.
Magnetic Field: The Moon has an external magnetic field of generally less than 0.2 nanoteslas, or less than one hundred thousandth that of Earth. The Moon does not currently have a global dipolar magnetic field and only has crustal magnetization. While the moon has no magnetic field of note today, recent evidence from rock samples brought back by the Apollo missions show that between 4.2 and 3.4 billion years ago, when the moon was more than twice as close to Earth as it is now, it did have a magnetic field that was at least as strong as Earth’s present magnetic field.