The Soviet Union remained active in robotic lunar exploration through the 1960s and 1970s. The first robotic lunar sample return mission took place with Luna 16 in September 1970, after multiple failed attempts with other missions.
The moon: Everything you need to know about Earth’s companion
The moon is Earth’s most constant companion and the easiest celestial object to find in the night sky.
The rhythm of the phases of the moon has guided humanity for millennia; for instance, calendar months are roughly equal to the time it takes to go from one full moon to the next. But the moon’s orbit and phases can seem mysterious. for example, the moon always shows us the same face, but it’s always changing size as how much of it we see depends on the moon’s position in relation to Earth and the sun.
While it’s a satellite of Earth, the moon, with a diameter of about 2,159 miles (3,475 kilometers), is bigger than Pluto. (And there are four other moons in our solar system even bigger than ours.)
The moon is a bit more than one-fourth (27%) the size of Earth, a much larger ratio (1:4) than any other moons to their planets. This means the moon has a great effect on our planet and may even be a major factor in making life on Earth possible.
Moon FAQs answered by an expert
We asked Chiara Ferrari-Wong, planetary scientist at the Hawai’i Institute of Geophysics and Planetology, a few frequently asked questions about the moon.
Chiara Ferrari-Wong
Planetary Scientist
Chiara Ferrari-Wong is a PhD Candidate and Graduate Research Assistant at the Hawaii Institute of Geophysics and Planetology, affiliated with the University of Hawai’i at Mānoa. Her research focuses on remote sensing instrumentation and the study of volatiles present on the moon.
How far is the moon from Earth?
On average, the moon is approximately 238,860 miles (382,500 km) away from Earth, equivalent to about 30 Earth diameters.
How big is the moon compared to Earth?
In terms of diameter, the moon is approximately one-fourth the size of Earth. When it comes to surface area, the Moon covers about 1/16th of Earth’s total surface area. In regards to mass, the moon has roughly 1.2% of Earth’s mass.
When is the moon closest to Earth?
The point in the moon’s orbit when it is closest to Earth is called perigee, often referred to as a “supermoon.” At perigee, the moon is approximately 224,000 miles (360,000 km) from Earth. During a supermoon, the moon appears about 14% larger than at its furthest point, known as apogee or a “micromoon,” it also appears around 30% brighter in the sky.
I believe it’s hard to distinguish between a supermoon and a micromoon with the naked eye, but it is easier to see the direct effects by observing the tides. A spring tide occurs during the full and new moons and is when the tidal range is the largest. During a supermoon’s spring tide, the tides exhibit approximately a 2-inch larger variation compared to regular spring tides. Conversely, during a micromoon’s spring tide, the tides have a 2-inch smaller variation than normal spring tides. This difference occurs because the gravitational pull of the moon is stronger when it is closer to Earth during perigee and weaker when it is farther away during apogee.
What would happen if the moon crashed into Earth?
The moon, which is relatively large compared to our planet, is believed to have formed as a result of a collision between Earth and a smaller Mars-sized planet, based on analysis of lunar samples and the similarities in composition between the moon and Earth. So, in a sense, the moon did collide with Earth in the past.
Currently, the moon is not on a trajectory to crash into Earth. It is gradually moving away from Earth at about 1.5 inches per year. The moon plays several important roles, such as stabilizing the tilt of our orbit, causing seasonal changes, influencing tides, and aiding nocturnal animal navigation. If the moon were to suddenly disappear, it would lead to significant environmental changes, and life on Earth, particularly animals, would face challenges in adapting to such drastic shifts. However, due to its slow departure, we do not notice substantial changes.
If, hypothetically, the moon were to crash into Earth, the consequences would be dire for all life. To put it into perspective, the asteroid that caused the extinction of dinosaurs was approximately 12 km in diameter, whereas the moon has a diameter of about [2,174 miles] 3,500 km — roughly 300 times larger. However, there is a concept called the Roche limit, which represents the minimum distance at which a large satellite (like the moon) can approach its primary body (Earth) without tidal forces tearing it apart. At approximately 11,500 miles above Earth, the gravitational forces from Earth would overpower the gravitational forces holding the moon together, causing it to break apart. Over time, the moon’s debris would rain down on Earth, burning in the atmosphere and leading to a warming climate beyond what life could survive. Ultimately, this catastrophic event could result in the extinction of life on Earth, except perhaps for some extremophiles.
How did the moon form?
There are various theories about how the moon was created, but recent evidence indicates it formed when a huge collision tore off a chunk of the primitive molten Earth, sending the raw ingredients for the moon into orbit.
Scientists have suggested the impacting object was likely about 10% the mass of Earth and about the size of Mars. Because Earth and the moon are so similar in composition, researchers have concluded that the impact must have occurred about 95 million years after the formation of the solar system, give or take 32 million years. (The solar system is roughly 4.6 billion years old.)
In 2015, new research gave further weight to this theory, using simulations of planetary orbits in the early solar system as well as newly uncovered differences in the abundance of the element tungsten-182 detected in the Earth and the moon.
While this theory, most commonly known as the large impact theory, is the dominant theory in the scientific community, there are several other ideas for the moon’s formation. These include the concept that the Earth captured the moon, that the moon fissioned out of the Earth or even that Earth may even have stolen the moon from Venus.
What is a waxing crescent moon?
In the day or so after every new moon, a slim smile of a moon – a waxing crescent – appears in the west shortly after sunset. Some people think a moon visible in the west after sunset is a rising moon. It’s not; it’s a setting moon. As Earth spins under the sky, all sky objects rise in the east and set in the west. A waxing crescent moon – visible in the western sky – quickly follows the sun below the western horizon.
Also, a waxing crescent moon has nothing to do with Earth’s shadow on the moon. Earth’s shadow can fall on the moon only at full moon, when the moon and sun are opposite each other – on either side of Earth – in space. When Earth’s shadow falls on the moon, we have a lunar eclipse.
That’s not the case on a waxing crescent moon. Such a moon lies not opposite the sun, but, on the contrary, on nearly the same line of sight to the sun, as seen from Earth. There is a shadow on a crescent moon, but it’s the moon’s own shadow. You know how night on Earth happens on the part of Earth submerged in Earth’s own shadow? The same is true on the moon. When you stand looking at a waxing crescent moon, you’re seeing a thin fraction of the moon’s day side, or illuminated side, and a larger fraction of the moon’s night side, the side of the moon submerged in the moon’s own shadow.
Earthshine on the waxing crescent moon
You might also see a pale glow on that night portion of the moon, when the moon is a crescent. That glow is called earthshine. It’s caused by the fact that – when we see a crescent moon in Earth’s sky – any moon people looking back at our world would see a nearly full Earth. Just as a full moon can illuminate an earthly landscape, so a full or nearly full Earth can illuminate the lunar landscape. And that’s what you’re seeing when you see earthshine. Read more about earthshine.
Because the waxing crescent moon is nearly on a line with Earth and the sun, its illuminated hemisphere – or day side – is facing mostly away from us. We see only a slender fraction of the day side: a crescent moon. Each evening, because the moon is moving eastward in orbit around Earth, the moon appears farther from the sunset glare. It is moving farther from the Earth-sun line in space. Each evening, as the moon’s orbital motion carries it away from the Earth-sun line, we see more of the moon’s day side. Thus the crescent in the west after sunset appears to wax, or grow fatter each evening.
More about moon phases
As the moon orbits Earth, it changes phase in an orderly way. Follow the links below to understand the phases of the moon.
Bottom line: A waxing crescent moon shines in the west after sunset. It quickly follows the sun below the western horizon.
