The Moon. Motion and phases of the Moon

The lunar surface. Physical and geological characteristics

The Moon’s surface features an inhospitable and desolate landscape that has remained virtually unchanged for billions of years due to the absence of a protective atmosphere and liquid water, which could cause erosion. When observing the Moon, two main types of terrain are clearly distinguishable: the highlands, which are mountainous, light-colored regions composed of ancient rocks called anorthosites, and the so-called lunar maria. These seas do not contain water; rather, they are vast dark plains formed by ancient basaltic lava flows that filled the craters left by the largest meteorites during the early days of the solar system.

The most characteristic feature of the lunar landscape is the immense number of impact craters covering its surface. Since it lacks an atmosphere to burn up meteoroids through friction before they hit the ground, and has no active geological processes such as plate tectonics or volcanism to erase them, the Moon preserves intact the scars of all the impacts it has received throughout its history. In addition, the entire lunar surface is covered by regolith, a grayish layer of fine dust and fragments of crushed rock produced by the constant bombardment of micrometeorites and solar radiation.

Lunar motion. The Moon’s rotation and translation

The Moon’s motion in space is governed by the laws of gravity, and, like the Earth, it performs two main motions simultaneously: rotation and translation. The combination of these motions determines the lunar cycles and defines exactly how we see our satellite from the Earth’s surface.

Rotation around its own axis

Rotation is the spinning motion the Moon performs on its own axis. The Moon takes approximately 27.3 days to complete one full rotation on its own axis, a period of time known in astronomy as a sidereal month. Unlike Earth, which spins at high speed, completing a rotation every 24 hours, the Moon’s rotation is extremely slow, causing days and nights on the Moon to last nearly two Earth days each.

The Moon’s orbital motion around the Earth

While rotating on its own axis, the Moon follows an elliptical orbit around the Earth due to the gravitational pull between the two bodies. Interestingly, the time it takes to complete one orbit around our planet is also about 27.3 days. Since both periods—rotation and revolution—last exactly the same amount of time, a physical phenomenon called synchronous rotation occurs. The direct consequence of this perfect synchrony is that the Moon always shows us the same hemisphere, leaving the so-called far side permanently invisible from Earth’s perspective.

The Moon’s gravitational influence on Earth

Despite the distance between them, Earth and the Moon are invisibly bound by a powerful gravitational interaction. According to the laws of physics, the Moon’s mass exerts a constant gravitational pull on our planet; although this force is not strong enough to move the continents, it has massive and vital effects on the Earth’s liquid masses and global dynamics.

The physical mechanism of high and low tides

The most visible effect of lunar gravity is the periodic rise and fall of ocean waters, a phenomenon known as tides. The Moon’s gravitational pull is stronger on the side of the Earth closest to it, causing the water to “bulge” toward the Moon. Surprisingly, on the opposite side of the Earth, another bulge also occurs due to centrifugal force and because the Earth is literally “pulled” away from the water on that side. As our planet rotates on its own axis every 24 hours, different coastal regions experience these bulges, resulting in two high-tide periods and two low-tide periods each day.

The stabilization of the earth’s rotation axis

Beyond its influence on ocean movements, the Moon plays a crucial role in the Earth’s habitability by acting as a gravitational regulator of its rotation axis. Our planet’s axis is tilted by about 23.5 degrees, which gives rise to the four seasons of the year. Without the Moon’s mass acting as a stabilizing counterweight, the gravitational forces of other giant planets like Jupiter would cause the Earth’s axis to wobble chaotically over time. By keeping that tilt fixed and stable, the Moon ensures that the global climate remains predictable and mild, allowing for the development and evolution of life as we know it.

The history of lunar exploration

The Moon has been the driving force behind humanity’s greatest scientific and engineering achievements. The quest to understand our natural satellite began with simple naked-eye observations in ancient times, evolved with the invention of the telescope, and culminated in the 20th century with humanity’s arrival on its surface.

Telescopic observation and the birth of selenography

The exploration of the Moon began thousands of years before the invention of rockets. Ancient astronomers from civilizations such as the Babylonian, Greek, and Chinese were already recording its cycles and eclipses. However, the true scientific revolution came in 1609, when Galileo Galilei first pointed a telescope at the Moon. Galileo discovered that the Moon was not a perfect, smooth sphere, but a world with mountains and deep valleys. From that moment on, astronomers such as Johannes Hevelius and Giovanni Riccioli began drawing the first detailed maps of the lunar surface (a discipline known as selenography) and named the geographical features “seas” and “craters”—terms we still use today.

The space race and reconnaissance missions

The shift from Earth-based observation to direct exploration took place in the mid-20th century, at the height of the Cold War. The Soviet Union led the first robotic successes with the Luna program: in 1959, the Luna 2 probe was the first human-made object to touch the Moon, and that same year, Luna 3 photographed the mysterious far side for the first time. In 1966, Luna 9 achieved the first soft landing in history. In response, NASA launched the Apollo program. On July 20, 1969, the Apollo 11 mission marked a historic milestone when Neil Armstrong and Buzz Aldrin walked on the lunar surface. By 1972, twelve astronauts had explored its surface, setting up scientific laboratories and bringing back to Earth 380 kilograms of rocks that revolutionized theories about the origin of the solar system.

Today, the Moon is entering a new era of international exploration focused on sustainable presence. The goal of current space programs, such as the Artemis project, is no longer to make temporary visits, but to establish stable scientific bases in strategic regions like the lunar south pole, using its ice reserves to generate water and fuel that will serve as a springboard to the rest of the solar system.