The celestial body known as Earth's natural satellite is the Moon. It is the fifth largest moon in the solar system and has been a focal point in human culture, science, and exploration. The Moon orbits Earth at an average distance of about 384,400 kilometers (238,855 miles) and has a significant effect on Earth, particularly through its influence on tides. The Moon's phases, resulting from its position relative to the Earth and Sun, have fascinated humanity for centuries. It has also been the subject of numerous space missions, most notably NASA's Apollo program, which landed the first humans on its surface.