The Moon: Definition, Age, Distance, Size, Surface, Facts

The Moon is Earth’s only natural satellite and the fifth largest moon in the solar system. The Moon’s age, diameter, and size define its physical properties. Its surface showcases a diverse range of terrain, including craters, mountains, and plains. The Moon plays a crucial role in shaping Earth’s tides and seasons through its gravitational pull. Learn about the Moon’s formation, orbital dynamics, and its effects on Earth’s geological and biological processes.

The Moon formed 4.51 billion years ago. Zircon crystals in lunar rocks support this age estimate. Studies of samples collected during Apollo missions have refined the Moon’s age range between 4.43 and 4.53 billion years. The Moon’s age is similar to that of the solar system, estimated to be 4.6 billion years old.

The Moon orbits Earth at an average distance of 384,400 kilometers (238,855 miles). Its orbit causes the distance to vary between 363,104 kilometers (225,622 miles) at perigee and 405,696 kilometers (252,088 miles) at apogee.  The Moon’s varying distance affects its appearance from Earth, appearing 14% larger and 30% brighter at perigee compared to apogee.

The Moon’s mass is 7.347 x 10^22 kg (16.2 x 10^22 lbs), which is 1/81 of Earth’s mass.   The Moon’s mass results in a surface gravity about 1/6 that of Earth’s.

The Moon consists of several layers. The core is composed of iron, nickel, and sulfur, with a radius of 330 km (205.05 miles). The mantle extends to a depth of 1350 km (839.9 miles) and consists of silicate minerals, olivine, and pyroxene. The crust has a thickness of 50 km (31 miles) and is composed of anorthosite, a rock containing plagioclase feldspar. Regolith, a mixture of dust and rock fragments, covers the Moon’s surface.

A lunar eclipse occurs when Earth aligns between the Sun and Moon. The Apollo program achieved the first human lunar landing with Apollo 11 in July 1969.

What is the Moon?

The Moon is Earth’s natural satellite, orbiting at an average distance of 238,855 miles (384,400 km). The Moon ranks as the fifth-largest moon in the solar system and largest relative to its parent planet. The Moon’s gravitational influence drives Earth’s tides and stabilizes its axis.

The Moon is a celestial body and natural satellite of Earth. Natural satellites are objects that orbit planets or other bodies in the solar system. The Moon influences  Earth’s systems and has impacts on our planet.

The Moon’s size is one-quarter of Earth’s diameter, measuring about 3,474 kilometers (2,159 miles) across. The Moon’s mass is 1.2% of Earth’s mass, making it the largest natural satellite relative to its parent planet in the solar system.  The Moon completes one orbit around Earth in 27.3 days, with an elliptical path having an eccentricity of 0.055.

The Moon formed 4.51 billion years ago, after the formation of Earth. The giant impact hypothesis is the most accepted theory for the Moon’s origin. This theory proposes that a Mars-sized body called Theia collided with Earth, ejecting debris that coalesced into the Moon. The Moon’s age is as old as the solar system itself, estimated to be 4.6 billion years old.

The Moon’s surface is characterized by a rocky, cratered terrain. Impact craters, maria (dark plains), and mountain ranges are features of the lunar scenery. The Moon’s surface is composed of rock and regolith, a layer of fragmented material. The Moon lacks an atmosphere and magnetic field, resulting in temperature variations and exposure to cosmic radiation.

Does the Moon have a name?

The Moon’s name is “Moon”. This celestial body’s designation originates from Proto-Germanic languages and has been recognized by the International Astronomical Union. “Luna” and “Selene” are used as alternative terms, but “Moon” remains the standard term.

Cultures and languages have given the Moon names throughout history. Greek mythology refers to the Moon as Selene, the goddess of the Moon. Cynthia serves as an epithet for the Moon, derived from Mount Cynthus, the birthplace of Artemis. Roman nomenclature uses Luna, which is employed in scientific writing and science fiction to differentiate Earth’s moon from others. Hindu tradition calls the Moon Chandra, representing the lunar deity in their mythology. Japanese culture refers to the Moon as Tsuki, which has significance in Japanese mythology.

The designation for Earth’s natural satellite remains “Moon” with a capital “M” to distinguish it as a proper noun. Luna and Selene are used as terms in certain contexts. Monikers and designations exist across cultures and languages. The term “lunar” is used in technical and scientific contexts to describe Moon-related phenomena. Despite the variety of names, the Moon does not have a unique name beyond its official designation as “Moon”.

How old is the Moon?

The Moon is estimated to be between 4.43 and 4.53 billion years old. This age range is based on analyses of lunar samples collected during Apollo missions. Zircon crystals in lunar rocks support an age estimate of 4.51 billion years.

A study using atom-probe tomography on zircon crystals collected by Apollo 17 astronauts determined the Moon’s age to be 4.46 billion years. This estimate is 40 million years older than the estimate of 4.42 billion years. Another study analyzing zircon crystals from the Apollo 14 mission indicated the Moon is at least 4.51 billion years old, making it 40 to 140 million years older than thought.

The estimated range for the Moon’s age is between 4.43 and 4.53 billion years. Previous common estimates placed the Moon’s age at around 4.35 billion years. Carlson and Lugmair’s 1988 study of anorthosite 60025, a rock, provided an age estimate of 4.44 billion years using Sm-Nd isotopic data. The new findings propose a “remelting event” occurred 4.35 billion years ago, resetting the Moon’s age and masking its true formation age.

How was the Moon formed?

The Moon formed when a Mars-sized object called Theia collided with Earth. This impact ejected debris into orbit, which coalesced to create Earth’s satellite 4.5 billion years ago. Scientists accept this theory today.

The impactor Theia had a mass one-tenth of Earth’s and was comparable in size to Mars. Theia’s composition was similar to Earth’s. The collision trajectory was a glancing blow. The impact theory explains the mechanics of this collision event. The impact imparted high angular momentum to the Earth-Moon system, resulting in a high angular momentum compared to other terrestrial planets. The collision ejected debris into orbit, forming a proto-lunar disk. Kinetic energy from the impact melted the ejecta, creating a global magma ocean on the Moon.

The proto-lunar disk consisted of vaporized and molten debris from both Earth and Theia. The disk’s material distribution and angular momentum led to the accretion of the Moon. Moonlets formed within the disk and merged to create the Moon. Earth’s gravitational field influenced the shaping of the Moon during its formation. The Moon formed with about half its current mass and orbited closer to Earth. Tidal friction caused the Moon to spiral outward over time, becoming tidally locked to Earth.

The Moon’s surface composition provides evidence of its origin. The lunar crust has an anorthositic composition, consistent with formation from a magma ocean. KREEP-rich samples support the existence of a lunar magma ocean. The Moon’s diameter is one-quarter that of Earth, making it the largest moon relative to its host planet in the solar system. The Moon’s orbital dynamics are consistent with formation outside Earth’s Roche limit. The Moon’s surface shows volatile depletion, with identical oxygen and titanium isotope ratios to Earth. Earth absorbed Theia’s core during the impact, explaining Earth’s high density compared to planets.

When was the Moon discovered?

The Moon was not discovered at a specific time. Humans have observed the Moon since ancient times. Galileo Galilei made telescopic observations of the Moon’s surface in 1609, revealing mountains and craters, which he published in Sidereus Nuncius in 1610.

The Moon has been known to humans since antiquity. Civilizations in Mesopotamia and Egypt recorded observations and worship of the Moon 25,000 to 35,000 years ago. The invention of the telescope in 1608 by Dutch spectacle makers, including Hans Lipperhey, marked an advancement in lunar observation. Galileo Galilei constructed a telescope based on descriptions of the Dutch invention and made his first telescopic observations of the Moon on November 30, 1609. Galileo’s observations revealed unknown lunar features, including mountains, craters, and an uneven surface. These findings challenged the prevailing Aristotelian view of the Moon as a sphere. Galileo published his observations in Sidereus Nuncius in 1610, which included drawings of the Moon’s surface. The publication of Galileo’s work initiated the epoch of detailed telescopic observation and mapping of the Moon, transforming our understanding of Earth’s companion.

How far is the Moon from Earth?

The Moon is at an average distance of 384,400 kilometers (238,855 mi) from Earth. Distance varies due to elliptical orbit, ranging from 363,104 kilometers (225,623 mi) at perigee to 405,696 kilometers (252,088 mi) at apogee.

The Moon’s orbit causes its distance from Earth to vary. At its closest approach, called perigee, the Moon comes within 363,104 km (225,623 miles) of Earth. The farthest point in the Moon’s orbit, known as apogee, places it 405,696 km (252,088 miles) from Earth. This variation in distance results in a difference of 42,592 km (26,465 miles) between perigee and apogee, exceeding three times Earth’s diameter.

The Moon’s varying distance affects its appearance from Earth. At perigee, the Moon appears 14% larger and shines 30% brighter compared to apogee. These variations lead to phenomena known as “supermoons” when the Moon is at perigee and “micromoons” when at apogee. The Moon’s distance from Earth is 393,821 km (244,000 miles), equivalent to 1.3136 light-seconds. Light takes 1.3 seconds to travel between Earth and the Moon at this distance.

What is the relationship between the Moon and Earth?

The relationship between the Moon and Earth is characterized by orbital dynamics. The Moon orbits around Earth in 27.32 days, revolving in sync with its orbital period. Earth’s gravity holds the Moon in orbit at a distance of 384,400 kilometers (238,855 miles). The Moon influences Earth’s tides and rotational rate.

The Moon revolves around Earth as its only natural satellite, completing one orbit in 27.3 days. Earth’s gravity maintains the Moon’s orbit through gravitational attraction. The Moon’s orbit varies in distance from 363,104 km (225,623 miles) at perigee to 405,696 km (252,088 miles) at apogee, with an average distance of 384,400 kilometers (238,855 miles). The Sun’s gravity influences the Moon’s orbit trajectory. The Moon-Earth relationship involves intricate orbital dynamics, with the Moon’s elliptical orbit resulting in varying distances over time.

The Moon’s gravity exerts an impact on Earth, causing tides by pulling on Earth’s oceans. Earth tides create two bulges – one facing the Moon and one on the opposite side. Tides fluctuation results in two high tides and two low tides every 24 hours and 25 minutes. Tides oscillation occurs due to the Moon’s orbital period and Earth’s rotation. The Moon exhibits tidal locking with Earth in a 1:1 spin-orbit resonance, causing the same side of the Moon to always face Earth.

What does the Moon do for the Earth?

The Moon affects Earth in three ways: creating tides, stabilizing Earth’s axis, and influencing biological rhythms. The Moon’s gravitational pull causes ocean tides, shapes coastlines, and impacts ecosystems. The Moon moderates Earth’s wobble, maintaining environmental stability. The Moon’s cycles guide animal behaviors and human activities.

The Moon’s gravitational force exerts an influence on Earth. Earth’s tidal response creates two daily high tides and two low tides. Tidal ranges vary from 0.003 meters (0.01 feet) to over 16 meters (52.49 feet). Water movement caused by tides shapes coastlines and impacts marine ecosystems. Tidal forces affect Earth’s crust, causing it to bulge by centimeters.

The Moon stabilizes Earth’s axial tilt at 23.5 degrees. Axial tilt stabilization prevents climate fluctuations and maintains seasons. Earth’s environmental stability has been essential for the growth and sustenance of life. The Moon’s influence on Earth’s axis has remained for billions of years.

Lunar illumination plays a part in Earth’s natural cycles. The Moon reflects about 12% of the sunlight it receives to Earth. Moonlight provides illumination with a characteristic silvery-blue tone. Lunar phases create an illumination cycle lasting 29.5 days. Animal behaviors are synchronized with the lunar cycle, including breeding, migration, and feeding patterns. Activities in pre-industrial societies have been influenced by lunar phases for agriculture, navigation, and cultural practices.

Does the Moon always face the Earth?

The Moon always faces the Earth due to synchronous rotation. The Moon’s rotation period matches its orbital period around Earth, taking 27.3 days. This tidal locking ensures the same side of the Moon faces our planet, while the far side remains concealed.

Tidal locking occurs through a mechanism involving Earth’s gravitational field. Earth’s gravity creates a tidal bulge on the Moon, acting as a brake to slow its rotation. The Moon’s rotation period matches its orbital period of 27.3 days around Earth. Angular velocity synchronization results from this gravitational interaction between Earth and Moon. Earth’s gravitational influence has maintained this tidal locking over billions of years, ensuring the Moon presents the same side to our planet.

The Lunar Near Side faces Earth due to synchronous rotation. The Lunar Far Side remains obscured from Earth’s view. Earth serves as a reference point for the Moon’s face orientation, with the nearside visible to Earth observers. The Moon keeps its axis pointed towards Earth as it orbits, maintaining this constant orientation.

Lunar Libration causes slight angular variations in the Moon’s face from Earth. Lunar libration involves a rocking and wobbling motion in the Moon’s orbit and rotation. Factors affecting libration include the Moon’s elliptical orbit and the tilt of its rotational axis relative to Earth’s equator. Libration allows Earth observers to see 59% of the Moon’s surface over time. The Moon’s face shows changes in perspective from Earth due to these libration effects. Earth observers can glimpse parts of the lunar surface just beyond the edge of the near side, while the far side remains invisible.

What is the mass of the Moon?

The mass of the Moon is 7.347 x 10^22 kg (1.620 x 10^23 lbs). The Moon’s mass is 1/81 of Earth’s mass. Earth weighs 81 times more than the Moon. The Moon’s density is 3.34 grams per cubic centimeter (0.12 pounds per cubic inch), 60% of Earth’s density.

An accurate figure for the Moon’s mass is 7.34767309 × 10^22 kg (1.62076 × 10^23 lbs). Researchers use values of 7.35 × 10^22 kg (16.2 × 10^22 lbs) or 7.347 × 10^22 kg (16.2 × 10^22 lbs) for simplicity. The Moon’s mass is expressed as 0.07346 × 10^24 kg (0.162 × 10^24 lb) to align with the order of magnitude used for Earth’s mass.

The Moon’s mass equals 8.1 × 10^19 tons. The Moon has a mass of 0.0123 × Earth’s mass. This equates to 1.2% of Earth’s mass. The Moon’s small mass compared to Earth results in its surface gravity being about 1/6 that of Earth’s.

What is the diameter of the Moon?

The diameter of the Moon is 2,159.2 miles (3,475 kilometers). Moon’s mean diameter is derived from its mean radius of 1,079.6 miles (1,737.5 kilometers). The Moon’s diameter is less than a third of Earth’s width.

The Moon’s mean diameter is 3,475 km (2,159.2 miles). Researchers use 3,476 km (2,160 miles) for simplicity. The Moon’s diameter can be expressed as 3,475,000 meters (11,400,000 feet).

Scientists round the Moon’s diameter to 3,500 km (2,175 miles) in metric units for simplicity. Imperial unit approximations include 2,160 miles (3,478 kilometers) or a rounded estimate of 2,100 miles (3,380 kilometers). These approximations are useful for comparisons or discussions about lunar dimensions.

What is the Moon made of?

The Moon is made up of layers. Its core consists of iron, nickel, and sulfur. The mantle contains olivine and pyroxenes. The crust is composed of oxygen, silicon, magnesium, iron, calcium, and aluminum, with an anorthositic composition.

The Moon’s core is composed of iron. Nickel and sulfur are present in smaller amounts. The core has a radius of 330 km (205.05 miles). A solid inner core of iron exists with a radius of 240 km (149.1 miles). The outer core is molten and contains up to 6% sulfur by weight.

The Moon’s mantle consists of silicate minerals. Olivine and pyroxene are the dominant minerals in the mantle. The mantle is rich in magnesium and iron. It extends to a depth of 1350 km (839.9 miles). Some regions of the mantle are molten.

The crust is composed of anorthosite. Anorthosite is a rock rich in plagioclase feldspar. The crust has an average thickness of 50 km (31 miles). It is thinner on the near side facing Earth and thicker on the far side. Basalts are present in the maria regions. These basalts are rich in iron and magnesium. Some lunar basalts contain abundances of titanium in the form of ilmenite.

The regolith covers the Moon’s surface. It is a mixture of dust and rock fragments. The regolith formed over billions of years due to meteoroid and asteroid impacts. Its thickness varies from about 6.6 feet (2 meters) in younger maria to 65.6 feet (20 meters) in older highlands. The regolith contains mineral fragments fused into glassy particles called agglutinates.

What is the Moon’s atmosphere?

The Moon’s atmosphere is an exosphere, a thin layer of gases composed of helium, neon, and argon. The Moon lacks breathable air. The Lunar atmosphere contains trace amounts of elements and is replenished by space weathering processes but lost due to weak gravity.

The Moon’s exosphere composition consists of helium, neon, and argon. Scientists estimate the lunar exosphere density at 80,000 atoms per cubic centimeter. Helium in the lunar atmosphere originates from the solar wind. The helium abundance ranges from 5,000 to 30,000 atoms per cubic centimeter. Hydrogen appears in small amounts in the lunar atmosphere. The hydrogen abundance is 17 atoms or less per cubic centimeter. Neon exists in the lunar atmosphere with concentrations up to 20,000 atoms per cubic centimeter. Argon in the lunar atmosphere comes from solar wind and radioactive decay. The argon abundance ranges between 20,000 to 100,000 atoms per cubic centimeter. Argon-40 freezes on the lunar surface at night and becomes mobile at sunrise. The lunar atmosphere pressure measures around 3×10^−15 atm (0.3 nPa). The Moon appears airless due to its thin atmosphere. The Moon does have a tenuous exosphere despite its appearance.

What color is the Moon?

The color of the Moon is gray or whitish-gray. The Moon’s surface materials reflect sunlight to create this appearance. The Moon appears yellow, orange, or red when viewed from Earth due to atmospheric conditions and position.

Observation from Earth reveals the Moon’s appearance as gray or whitish-gray. The Moon looks black and white to the naked eye due to contrast against the sky. Atmospheric conditions cause the Moon to appear orange when low on the horizon or during events with increased atmospheric particles.

The Moon’s surface coloration varies when observed up close or through imaging. Sunlit areas of the Moon appear white to brown-gray when viewed on the lunar surface. Titanium regions on the Moon exhibit a blue tint in false-color images. Iron areas on the Moon’s surface display red or orange hues in visualizations.

The Moon takes on a pink or red appearance during a total lunar eclipse, referred to as a “blood moon”. This color change results from Earth’s shadow blocking direct sunlight and only allowing filtered light to reach the lunar surface.

What shape is the Moon?

The Moon’s shape is a scalene ellipsoid, approximating a triaxial ellipsoid rather than a perfect sphere. Its three axes have different lengths, but the differences are minimal. For purposes, the Moon is considered spherically symmetric.

What are some interesting facts about the Moon?

Facts about the Moon include that it is Earth’s only natural satellite, has a diameter of 3,476 kilometers (2,159 miles), and is one-quarter Earth’s size. The Moon orbits Earth, completing one orbit in 27.3 days. The Moon’s surface has mountains, craters, and lava plains.

Some interesting facts about the Moon are listed below.

• The Moon is Earth’s only natural satellite.
• The Moon has a diameter of 3,476 kilometers (2,159 miles), one-quarter of Earth’s size.
• The Moon completes one orbit around Earth in 27.3 days.
• The Moon’s surface features include mountains, craters, and lava plains.
• The Moon’s gravitational pull causes Earth’s ocean tides.
• The Moon’s formation occurred approximately 4.51 billion years ago.
• The Moon is at an average distance of 238,855 miles from Earth, varying between 225,623 and 252,088 miles.
• The Moon’s surface features lunar maria which are dark basaltic lava plains formed by volcanic eruptions.
• The lunar phases are determined by the Sun’s illumination as the Moon orbits Earth.
• A lunar eclipse happens when Earth aligns between the Sun and Moon.
• The Impact Hypothesis suggests that the Moon formed from a collision between Earth and another object.
• The Apollo program began with the first human lunar landing with Apollo 11 in July 1969.
• NASA’s Artemis program plans to return humans to the Moon by 2025 for further research.