The Moon: Earth’s Only Natural Satellite
The Earth is the closest planet to the Sun with a natural satellite. Mercury and Venus have none while its neighbor, Mars, has two moons. It is far cry from Saturn which has 82 moons and counting!
The Moon shines with an apparent magnitude of −2.5 to −12.9 and is the brightest object in our night sky. However, it is important to note that, like Earth, the Moon does not produce its own light. This silvery orb shines because it reflects light from the Sun.
The Moon not only provides us with natural light at night. It is also responsible for many other things that make life possible.
The gravitational pull of the Moon causes the high tide and low tides in our oceans. This, in turn, distributes the nutrients in our oceans and makes life possible for oceanic life. Also, the Moon helps moderate the wobble of our planet and affects our overall climate.
Aside from our home planet, Earth, the Moon is the only other celestial object that humans have set foot on.
Knowing about the Earth-Moon distance makes us better understand the effects of our natural satellite on us.
The Lunar Cycle
The Moon is in synchronous rotation with Earth. What this means is that it takes the Moon the same time to rotate on its axis and orbit around Earth. As a result, only one side of the Moon is constantly facing Earth. The other side of the Moon that does not face Earth is more correctly called the “far side” not the “dark side.”
The Moon goes through a cycle as it travels in its orbit. It is the reason why the Moon seems to have different shapes every night. Sometimes it looks like a fully circular disk, while other times it can have a crescent shape. There are even times that it is invisible in our night sky.
The changing of the Moon’s shape is a result of the Lunar Cycle. It undergoes a series of apparent changes as it orbits around Earth. These phases unfold through the synodic lunar month which is 29.5 days long. However, the Moon completes an orbit around Earth in only 27.3 days. This is called the sidereal lunar month.
Throughout the different phases, the Moon can look smaller or bigger depending on its distance from Earth.
The phases of the Moon are:
- The New Moon
- Waxing Crescent
- First Quarter
- Waxing Gibbous
- The Full Moon
- Waning Gibbous
- Third Quarter/ Last Quarter
- Waning Crescent
The Moon’s phases and its distance to us can affect lunar phenomena such as solar eclipses, lunar eclipses, and supermoons.
How Far Away Is the Moon From Earth?
The Moon is the brightest object in our night sky. A big part of this is because of its distance to us. Aside from being our one and only natural satellite, the Moon is also our closest celestial neighbor.
But how close is it?
We often hear about the term “average distance” when talking about how far the Moon is. We say “average” because the Moon’s orbit is not perfectly circular. And since it is not a perfect circle, its distance from Earth is not always the same.
When the Moon is at the farthest point of its orbit, it is 405,696 kilometers (252,088 miles) away from Earth. When it is the closest to us, it is 363,105 kilometers (225,623 miles) away.
The Moon’s distance from Earth varies over time, depending on where it is in its orbit. Because of this, we use “average distance” to get an idea of how far it is without having to go through its greatest and least distances.
Though the Moon looks close to Earth as we see in pictures, they are actually far apart. On average, the Moon is 384,400 km or 238,855 miles away from Earth. Since the Earth’s diameter is 12,742 km or 7,917 miles, we can put about 30 Earths between our planet and the Moon.
Closest and Farthest Moons in the Solar System
To compare, the closest moon to its planet in the solar system is the Phobos moon of Mars. This is the larger of the two Martian moons, the other one being Deimos.
It is located only 9,376 kilometers (5,826 miles) away from the red planet. This moon is also getting closer to Mars, and will likely crash into the planet into the far future.
In contrast, the farthest moon to its planet is the irregular moon Neso of Neptune. It follows a very eccentric orbit that can take it millions of kilometers away from its host planet. On average, Neso is 49,285,000 kilometers (30,624,279 miles) away from the ice giant Neptune.
Distance of the Moon: Perigee and Apogee
The Moon travels in an elliptical path around Earth. It is not completely round, but a slightly elongated circle. Because of this, the Moon’s distance to Earth varies depending on where it is in its orbit.
Perigee is the Moon’s closest approach to Earth. On the other hand, it is apogee when the Moon is farthest from us. Together, these extreme points are called apsides (singular: apsis).
Below is the Moon’s average distance to us during apsides.
- Perigee- 363,105 kilometers (225,623 miles)
- Apogee- 405,696 kilometers (252,088 miles)
There is a significant difference when the Moon is at these points. During perigee or its closest point, the Moon is between 28 to 29 Earths. In apogee, however, it becomes 32 Earths away from us. These differences have certain effects on Earth.
If a full moon happens on a perigee, a supermoon occurs. This interesting event makes the Moon appear bigger in our night sky. In fact, it becomes about 14% bigger and 30% brighter than when the Moon is at apogee. Also, the Moon appears 7% bigger this time than the usual full moon.
When the Sun, Moon, and Earth are aligned during New Moon or Full Moon, we get “spring tides.” During spring tides, high tides are higher and low tides are lower. Spring tides that occur when the Moon is closest to us are called “perigean spring tides.”
The opposite of a supermoon is a micromoon. It is when a full moon coincides with apogee, the point where the Moon is the farthest from us. Since it is the farthest, the full moon looks smaller and dimmer as seen in our sky.
How Far is the Moon from the Sun?
The Sun is the center of the solar system and everything moves around it, except moons. While the Earth orbits the Sun, the Moon, in turn, orbits Earth.
Since the Earth and Moon move together in space, their distance from the Sun is about the same. On average, the Moon and Earth are roughly 150 million kilometers or 93 million miles from the Sun. This distance equals 1 astronomical unit (AU).
We sometimes use AU when talking about how far other celestial bodies are. This way, we can get an idea of how far they are relative to the Earth-Sun distance (or the Moon-Sun distance).
Light travels at a speed of 299,792 kilometers per second or 186,287 miles per second. With this speed, sunlight takes about 8 minutes to reach Earth. This is also about the same time it reaches the Moon. After sunlight reflects on the Moon, it reaches Earth in the form of “moonlight.”
The light from the Moon only takes about 1.26 light seconds to reach Earth. This is because the Moon is much closer to the Earth than the Sun is.
Perihelion and Aphelion
Like the Moon, the Earth also follows an elliptical orbit. Because of this, there will be times when the Earth is closest and farthest to the Sun.
Perihelion is when the Earth is at its nearest point to the Sun. On the other hand, it is in aphelion when it reaches its farthest point. The Earth is at perihelion in early January while it is in aphelion in early July.
Below is the Earth’s average distance to the Sun in perihelion and aphelion:
- Perihelion- 147,000,000 km (91,341,565 miles)
- Aphelion- 152,000,000 km (94,448, 421 miles)
How Long Will It Take To Get to the Moon From Earth?
It would take about three days to get the Moon. This is the average time it took for most lunar missions to reach our only natural satellite.
Remember that the Moon is, on average, 384,400 kilometers or 238,855 miles away from Earth. Given the average distance and travel time, it is safe to say that those that visited the Moon traveled at a speed of around 5,364 kph (3,333 mph).
Also, if one decides to embark on this journey, there are many factors to be considered.
Firstly, you should think about the reason why you would go to the Moon in the first place. If your mission is to take a closer look at the Moon, then your spacecraft needs to slow down to be able to enter the Moon’s orbit. But if you just want to pass it, then the spacecraft can travel faster.
While it can take just days to reach the Moon, some lunar missions can take more than a year. An example of this is the SMART-1 mission of the European Space Agency (ESA). However, this trip took longer because it was designed to do so. Using an ion engine, it is one of the most fuel-efficient missions in space.
Other uncrewed missions also took more than the average three days of travel time. China’s Chang’ e orbiters took around four to five days to reach the Moons.
Notable Missions to the Moon
One of the fastest trips to the Moon took only 34 hours. This was the Luna 1 probe of the Soviet Union. Not only was it the first to reach the Moon’s vicinity, but it also remains among the fastest missions even today. The first spacecraft to reach and crash on the lunar surface was Luna 2.
Holding the record for the shortest travel time to get to the Moon is the New Horizons missions. It only took 8 hours and 35 minutes to pass by the Moon. It did not slow down as it headed into the outer solar system. Of the Apollo missions, Apollo 11 was the first spacecraft that bought man to the Moon. Travel time was 3 days, 3 hours, and 49 minutes
The Artemis Mission
NASA’s last crewed mission to the Moon was Apollo 17 in 1972. However, this would likely change soon as the agency set out the Artemis Program.
The Artemis Mission is NASA’s latest program to the Moon. This crewed mission aims to land “the first female astronaut and the first astronaut of color” on the Moon.
Not only this, but the Artemis mission will also serve as the basis for the bigger and bolder goal of landing on Mars. Through this mission, NASA will build the Artemis Base Camp on the Moon and a space station (Gateway) in lunar orbit.
The Artemis program started in 2017. It has 3 missions:
- In order, Artemis 1
- Artemis 2
- Artemis 3
The Artemis 1 mission was set to get to the Moon by 2024. However, it was delayed to 2025. The next two missions will follow based on the development of the first one.
Below is the meaning of the Artemis 1 logo as explained by NASA:
- A
The A symbolizes an arrowhead from Artemis’ quiver and represents launch.
- Tip of the A
The tip of the A of Artemis points beyond the Moon and signifies that our efforts at the Moon are not the conclusion, but rather the preparation for all that lies beyond.
- Moon
- The Moon is our next destination and a stepping stone for Mars. It is the focus of all Artemis efforts.
- Red Trajectory
The trajectory moves from left to right through the crossbar of the “A” opposite that of Apollo. Thus highlighting the distinct differences in our return to the moon. The trajectory is red to symbolize our path to Mars.
- Blue Earth Crescent
The crescent shows missions from our audience’s perspective. From Earth we go. Back to Earth all that we learn and develop will return. This crescent also visualizes Artemis’ bow as the source from which all energy and effort is sent.
How About Driving From Earth to the Moon?
If hypothetically, one were to drive to the Moon, this trip would take just under 6 months. That is if they would drive at a speed of 95km/h (60mph). This duration is equivalent to 10 times of driving around the world!
While this may sound like an exciting thing to do, driving to the Moon would mean you have to drive upwards. Gasoline would be another problem too. Your car needs to have a gigantic tank to carry fuel that would last about half a year. It would be convenient if there were gas stations on the way, wouldn’t it?
Another thing to consider is the atmosphere the driver needs to breathe. That said, driving to the Moon would be a no ordinary affair that requires no ordinary car.
Is the Moon Getting Closer or Further Away?
The Moon is getting farther from Earth by 3.78cm (1.48in) per year. This is about the same rate that our fingernails grow.
The Moon has been continually drifting over time since its formation. Around 4.5 years ago, it was thought that the Moon was way closer to Earth at only about 22,500 km (13,981 mi). With this distance, the Moon looks 17 times bigger in the sky than it does now. Also, a day’s length is only 5 hours long!
The Moon is spinning away from us because of its interaction with the oceans of the Earth. Without the Moon that stabilizes the Earth’s wobble, our blue planet would become unstable. While this may sound like a terrible thing, this process would take billions of years to affect life on Earth—way beyond our lifetime!
How the Moon Affects Earth: Could We Survive Without It?
The Sun is the most important thing in the solar system. But for Earth, the Moon can be just as important. Aside from being the brightest object at night, the Moon also regulates our tides, the animal sleep cycle, the climate, and the length of the day, among others.
So could we survive without it? We probably can if, as a species, we can adapt over time, but there would be so many changes.
If the Moon were to disappear, the planet Venus would be the brightest object in the night sky. But since it is much fainter than our Moon, our nights would turn much darker than it is now.
We would still have ocean tides without the Moon, but they would be smaller. The Sun has tidal effects on Earth but since it is much farther, it is not as significant as the lunar tides. If this is the case, the tides would only be about one-third the size of our tides today.
The Moon is like the “stabilizer” of Earth. At present, the Earth remains tilted at 23.5 degrees, which causes the seasons around the globe.
If the Moon were to vanish, the Earth would wobble, causing it to tumble on its axis. The days would be much shorter and the climate and the temperature differences would be much more extreme, or there could be no seasons at all.
The Moon is moving 3.78 cm (1.48 in) away from us every year. Still, it would take a very long time for its effect to have serious effects on living things on Earth. By this time, the Sun would have already become a red giant. Our star would have grown so much in size that it would have swallowed the inner solar system, including the Earth and Moon.
More Moon Facts
- The Moon is 3.7 times smaller than Earth.
The Earth’s radius measures 6,371.00 km while its Moon has a radius of 1,737.5 km. With this size, the Moon is the fifth-largest natural satellite in the solar system. The first four are Ganymede (Jupiter), Titan (Saturn), Callisto (Jupiter), and Io (Jupiter)
Interestingly, our Moon is the second-densest natural satellite in the solar system. The first one is Jupiter’s Galilean moon Io.
- The Moon is about 400 times smaller than the Sun.
While the Moon’s diameter is only 3,475 km, the Sun is 1.4 million km across. The interesting thing is that the Sun is also about 400 times farther than the Moon is. Because of this, the Moon and Sun look like they are the same size in our sky.
- The Apollo astronauts took longer to reach the Moon than they did coming back from the Moon to Earth.
To compare, their travel time going to the Moon was 3 days, 3 hours, and 49 minutes. Going back home, they only took 2 days, 22 hours, and 56 minutes. The reason for this is orbital mechanics. It just so happened that Moon’s orbit took it closer to Earth while the astronauts were still up there.
- There will be no more total solar eclipses in the far future.
Solar eclipses occur when the Moon fully covers the Sun’s disk as seen on Earth. However, the Moon is slowly moving farther from Earth at a rate of 3.8 centimeters per year.
Also, the Sun is slowly growing as it moves closer to the red giant stage. With the Moon getting farther and the Sun growing, the Moon will not be able to completely cover the Sun’s disk. However, this would take billions of years to occur.
- Aside from footprints, astronauts Neil Armstrong and Buzz Aldrin left mirrors on the Moon.
One of the most important feats of the Apollo 11 mission was the “lunar laser ranging retroreflector array.” The mirrors are in the panel are “corner-cube reflectors,” which means they reflect any pulse that hit them.
Astronomers shoot laser pulses from Earth hitting the lunar reflector. They then catch the faint reflections that bounce back to Earth. Through the Lunar Laser Ranging Experiment, we can have precise measurements of how far away the Moon is from Earth.
Sources:
https://spaceplace.nasa.gov/moon-distance/en/
https://www.space.com/18145-how-far-is-the-moon.html
https://www.esa.int/Enabling_Support/Operations/SMART-1
https://www.rmg.co.uk/stories/topics/nasa-moon-mission-artemis-program-launch-date
https://www.nasa.gov/specials/artemis/
https://www.sciencefocus.com/space/if-you-could-drive-a-car-upwards-at-60mph-how-long-would-it-take-to-get-to-the-moon/
https://sciencenorway.no/forskningno-norway-planets/what-would-we-do-without-the-moon/1433295
https://www.insidescience.org/video/what-would-happen-if-there-were-no-moon
https://solarsystem.nasa.gov/moons/earths-moon/by-the-numbers/
(https://earthsky.org/space/coincidence-that-sun-and-moon-seem-same-size/)
https://science.nasa.gov/science-news/science-at-nasa/2004/21jul_llr
Image Sources:
The Moon: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c7/Moon_viewed_by_Hodoyoshi_satellite.jpg/1200px-Moon_viewed_by_Hodoyoshi_satellite.jpg?20160820154057
The Lunar Cycle: https://www.oercommons.org/editor/images/737
How Far Away Is the Moon From Earth?: https://www.perkinselearning.org/sites/elearning.perkinsdev1.org/files/styles/node_highlighted_image/public/earthmoon.jpg?itok=anvea795
Distance of the Moon: Perigee and Apogee: https://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Apogee_%28PSF%29.svg/1280px-Apogee_%28PSF%29.svg.png
How Far is the Moon from the Sun?: https://imageio.forbes.com/specials-images/imageserve/5f35b0d4040f40bc2897d3c2/Total-solar-eclipses-occur-when-the-Moon-crosses-the-Earth-Sun-line-at-close/0x0.jpg?fit=crop&format=jpg&crop=960,540,×0,y0,safe (Flickr user Kevin Gill)
How Long Will It Take To Get to the Moon From Earth?: https://upload.wikimedia.org/wikipedia/commons/thumb/2/2b/NASA_AS-11-40-5875.jpg/893px-NASA_AS-11-40-5875.jpg?20060426161739
The Artemis Mission: https://www.nasa.gov/specials/artemis/img/logo-annotations.png
Is the Moon Getting Closer or Further Away?: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/AS08-14-2383.jpg/800px-AS08-14-2383.jpg
How the Moon Affects Earth: Could We Survive Without It?: https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Bat_flying_on_the_backdrop_of_Moon.jpg/1024px-Bat_flying_on_the_backdrop_of_Moon.jpg