Earth's Moon

Although not a planet in the strict sense of the word, the Moon is so important to Earth that it is decided that it warrants its place with the other planets.

Basic Facts and Dimensions

The Moon, Earth’s only natural satellite, is one of the most prominent and studied celestial bodies in the solar system. It orbits our planet at an average distance of about 384,400 kilometers and has a diameter of roughly 3,474 kilometers, making it the fifth largest moon in the solar system. Despite its smaller size compared to Earth, the Moon has a profound influence, shaping tides, stabilizing Earth’s tilt, and impacting the evolution of life.

Surface Features

One of the most striking characteristics of the Moon is its cratered surface. Billions of years of impacts from asteroids and comets have left scars that remain visible, since the Moon lacks a thick atmosphere to erode them away. Alongside these craters are vast plains called maria—dark basaltic regions formed by ancient volcanic activity. In contrast, the bright lunar highlands, composed mainly of anorthosite, provide the mottled look we see from Earth.

Harsh Environment

The Moon’s environment is extremely hostile. Without a protective atmosphere, it experiences dramatic temperature swings: scorching daytime highs of about 127°C and frigid nighttime lows near –173°C. The absence of an atmosphere also means the sky is pitch black, even during daylight. Its surface is covered by fine, abrasive dust called regolith, which clings to equipment and proved challenging for astronauts during the Apollo missions.

Gravitational Influence on Earth

The gravitational pull between the Moon and Earth is a defining feature of their relationship. The Moon generates ocean tides, which have shaped coastal landscapes and ecosystems for billions of years. Additionally, it stabilizes Earth’s axial tilt, preventing extreme climatic variations. Over time, the Moon is slowly drifting away from Earth at a rate of about 3.8 centimeters per year, a fact measured with precision using laser reflectors left by Apollo astronauts.

Origin and Formation

The most widely accepted explanation for the Moon’s origin is the giant impact hypothesis. Around 4.5 billion years ago, a Mars-sized body likely collided with the young Earth, ejecting material that eventually formed the Moon. This theory explains the Moon’s similarity to Earth’s mantle in composition as well as its relatively small iron core.

Cultural and Scientific Importance

Throughout history, the Moon has inspired mythology, art, calendars, and navigation methods. Its phases were among humanity’s first tools for measuring time. Scientifically, it became the stage for humankind’s first ventures into space beyond Earth. Between 1969 and 1972, NASA’s Apollo missions achieved the first crewed lunar landings, a milestone in exploration and technology.

Future Exploration

Today, the Moon is again at the forefront of exploration. Programs such as NASA’s Artemis aim to establish a long-term human presence on its surface, using it as a training ground and launchpad for missions to Mars and deeper into the solar system. The Moon’s geology, resources, and proximity make it a vital stepping stone in humanity’s journey beyond Earth.