What Is The Difference Between Asteroids and Meteorites?

Asteroids, meteors, and meteorites … It might be fair to say these rocks from space inspire both wonder and fear among us Earthlings. But knowing a bit more about each of them and how they differ may eliminate some potential misgivings. While all these rocks originate from space, they have different names depending their location — i.e. whether they are hurtling through space or hurtling through the atmosphere and impacting Earth’s surface.

In simplest terms here are the definitions:

Asteroid: a large rocky body in space, in orbit around the Sun.

Meteoroid: much smaller rocks or particles in orbit around the Sun.

Meteor: If a meteoroid enters the Earth’s atmosphere and vaporizes, it becomes a meteor, which is often called a shooting star.

Meteorite: If a small asteroid or large meteoroid survives its fiery passage through the Earth’s atmosphere and lands on Earth’s surface, it is then called a meteorite.

Another related term is bolide, which is a very bright meteor that often explodes in the atmosphere. This can also be called a fireball.

Let’s look at each in more detail:

Asteroids

An artists impression of an asteroid belt. Credit: NASA
An artists impression of an asteroid belt. Credit: NASA

Asteroids are found mainly in the asteroid belt, between Mars and Jupiter. Sometimes their orbits get perturbed or altered and some asteroids end up coming closer to the Sun, and therefore closer to Earth. In addition to the asteroid belt, however, there have been recent discussions among astronomers about the potential existence of large number asteroids in the Kuiper Belt and Oort Cloud. You can read a paper about this concept here, and a good article discussing the topic here.

The asteroid Vesta as seen by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA
The asteroid Vesta as seen by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

Asteroids are sometimes referred to as minor planets or planetoids, but in general, they are rocky bodies that do not have an atmosphere. However, a few have their own moons. Our Solar System contains millions of asteroids, many of which are thought to be the shattered remnants of planetesimals – bodies within the young Sun’s solar nebula that never grew large enough to become planets.

The size of what classifies as an asteroid is not extremely well defined, as an asteroid can range from a few meters wide – like a boulder — to objects that are hundreds of kilometers in diameter. The largest asteroid is asteroid Ceres at about 952 km (592 miles) in diameter, and Ceres is so large that it is also categorized as a dwarf planet.

Most asteroids are made of rock, but as we explore and learn more about them we know that some are composed of metal, mostly nickel and iron. According to NASA, a small portion of the asteroid population may be burned-out comets whose ices have evaporated away and been blown off into space. Recently, astronomers have discovered some asteroids that mimic comets in that gas and dust are emanating from them, and as we mentioned earlier, there appears to be a large number of bodies with asteroid-like compositions but comet-like orbits.

How Often Do Asteroids Hit Earth?

Meteor Crater near Winslow, Arizona. Image credit: NASA.
Meteor Crater near Winslow, Arizona. Image credit: NASA.

While we know that some asteroids pass very close to Earth’s orbit around the Sun, we’ve been lucky in the history of humanity that we haven’t had a large asteroid hit Earth in the past several thousand years. It wasn’t until satellite imagery of Earth became widely available that scientists were able to see evidence of past asteroid impacts.

One of the more famous impact craters on Earth is Meteor Crater in Arizona in the US, which was made by an impact about 50,000 years ago. But there are about 175 known impact around the world – a few are quite large, like Vredefort Crater in South Africa which has an estimated radius of 190 kilometers (118 miles), making it the world’s largest known impact structure on Earth. Another notable impact site is off the coast of the Yucatan Peninsula in Mexico, and is believed to be a record of the event that led to the extinction of the dinosaurs 65 million years ago. You can see images of some of the most impressive Earth impact craters here.

These days, asteroid impacts are less of a threat. NASA estimates that about once a year an automobile-sized asteroid enters Earth’s atmosphere, creates an impressive fireball and disintegrates before ever reaching the surface. Studies of Earth’s history indicate that about once every 5,000 years or so on average an object the size of a football field hits Earth and causes significant damage. Once every few million years on average an object large enough to cause regional or global disaster impacts Earth. You can find more information about the frequency of impacts in this article from NASA.


Meteors, Meteoroids and Bolides

A bright meteor from September 21, 1994. Credit: John Chumack.
A bright meteor from September 21, 1994. Credit: John Chumack.

Space debris smaller than an asteroid are called meteoroids. A meteoroid is a piece of interplanetary matter that is smaller than an asteroid and frequently are only millimeters in size. Most meteoroids that enter the Earth’s atmosphere are so small that they vaporize completely and never reach the planet’s surface. When they burn up during their descent, they create a beautiful trail of light known as a meteor, sometimes called a shooting star.

Mostly these are harmless, but larger meteors that explode in the atmosphere – sometimes called bolides — can create shockwaves, which can cause problems. In February 2013 a meteor that exploded over Chelyabinsk, Russia shattered windows with its air blast. This meteoroid or bolide was estimated to be 18 meters (59 feet) in diameter. In 1908, a rocky meteoroid less than 100 meters in diameter is believed to have entered the atmosphere over the Tunguska region of Siberia in 1908 and the resulting shockwave knocked down trees for hundreds of square kilometers

How often is Earth hit by meteroids?

Chelyabinsk fireball recorded by a dashcam from Kamensk-Uralsky north of Chelyabinsk where it was still dawn.
Chelyabinsk fireball recorded by a dashcam from Kamensk-Uralsky north of Chelyabinsk where it was still dawn.

Because of the Chelyabinsk meteor in 2013, astronomers have acquired more information about the frequency of larger meteors that hit Earth, and there is now a growing consensus that the Earth gets hit by bigger space rocks more often than we previously thought. You can read more about that concept here.

This video from the B612 Foundation shows a visualization of the location of 26 space rocks that hit Earth between 2000 and 2013, each releasing energy equivalent to some of our most powerful nuclear weapons. The B612 foundation says that a Hiroshima-scale asteroid explosion happens in our atmosphere on average once a year, but many are not detected because they explode high in the atmosphere, or because most of the Earth’s surface is water and even a large percentage of land is fairly uninhabited by humans.

Estimates vary of how much cosmic dust and meteors enter Earth’s atmosphere each day, but range anywhere from 5 to 300 metric tons. Satellite observations suggest that 100-300 metric tons of cosmic dust enter the atmosphere each day. This figure comes from the rate of accumulation in polar ice cores and deep-sea sediments of rare elements linked to cosmic dust, such as iridium and osmium.

But other measurements – which includes meteor radar observations, laser observations and measurements by high altitude aircraft — indicate that the input could be as low as 5 metric ton per day. Read more about this here.

For a documented list of bolide events, you can check out this page from JPL.

Meteorite

A stunning slice of the Glorieta pallasite meteorite cut thin enough to allow light to shine through its many olivine crystals.  Credit: Mike Miller
A stunning slice of the Glorieta pallasite meteorite cut thin enough to allow light to shine through its many olivine crystals. Credit: Mike Miller

If any part of a meteoroid survives the fall through the atmosphere and lands on Earth, it is called a meteorite. Although the vast majority of meteorites are very small, their size can range from about a fraction of a gram (the size of a pebble) to 100 kilograms (220 lbs) or more (the size of a huge, life-destroying boulder). Meteorites smaller than 2mm are classified as micrometeorites.

Meteorites have traditionally been divided into three broad categories, depending on their structure, chemical and isotopic composition and mineralogy. Stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites that are largely composed of metallic iron-nickel; and, stony-iron meteorites that contain large amounts of both metallic and rocky material.

Meteorites have also been found on the Moon and Mars and conversely, scientists have traced the origination of the meteorites found here on Earth to four other bodies: the Moon, Mars, the asteroid 4 Vesta, and the comet Wild 2. Meteorites are the source of a great deal of the knowledge that we have have about the composition of other celestial bodies.

How Often Do Meteorites Hit Earth?

On Feb. 28, 2009, Peter Jenniskens (SETI/NASA), finds his first 2008TC3 meteorite after an 18-mile long journey. "It was an incredible feeling," Jenniskens said. The African Nubian Desert meteorite of Oct 7, 2008 was the first asteroid whose impact with Earth was predicted while still in space approaching Earth. 2008TC3 and Chelyabinsk are part of the released data set. (Credit: NASA/SETI/P.Jenniskens)
On Feb. 28, 2009, Peter Jenniskens (SETI/NASA), finds his first 2008TC3 meteorite after an 18-mile long journey. “It was an incredible feeling,” Jenniskens said. The African Nubian Desert meteorite of Oct 7, 2008 was the first asteroid whose impact with Earth was predicted while still in space approaching Earth. 2008TC3 and Chelyabinsk are part of the released data set. (Credit: NASA/SETI/P.Jenniskens)

According to the Planetary Science Institute, it is estimated that probably 500 meteorites reach the surface of the Earth each year, but less than 10 are recovered. This is because most fall into water (oceans, seas or lakes) or land in remote areas of the Earth that are not accessible, or are just not seen to fall.

You can read more about meteorites that were found from the Chelyabinsk meteor here.

Summary

In short, the difference between asteroids and meteors all comes down to a question of location. Asteroids are always found in space. Once it enters an atmosphere, it becomes a meteor, and then a meteorite after it hits the ground. Each are made of the same basic materials – minerals and rock – and each originated in space. The main difference is where they are when they are being observed.

We have many great articles on the subject of asteroids and meteorites here at Universe Today, such as this general information article on asteroids, this article and infographic about the difference between comets, asteroids and meteors, and these articles that deal with Ceres and Vesta. And here are some recent articles about the Chelyabinsk meteor that landed in Russia, as well as a 2 billion-year old Martian meteorite that contains evidence of water on Mars.

There is some good information on a NASA page as well as some great information here on Universe Today and Astronomy Cast.

Sources:
JPL’s Near Earth Asteroid Office
Planetary Science Institute
NASA: Asteroids
NASA: Meteors

What is Lunar Regolith?

When you’re walking around on soft ground, do you notice how your feet leave impressions? Perhaps you’ve tracked some of the looser earth in your yard into the house on occasion? If you were to pick up some of these traces – what we refer to as dirt or soil – and examine them beneath a microscope, what would you see?

Essentially, you would be seeing the components of what is known as regolith, which is a collection of particles of dust, soil, broken rock, and other materials found here on Earth. But interestingly enough, this same basic material can be found in other terrestrial environments as well – including the Moon, Mars, other planets, and even asteroids.

Definition:

The term regolith refers to any layer of material covering solid rock, which can come in the form of dust, soil or broken rock. The word is derived from the combination of two Greek words – rhegos (which means “blanket”) and lithos (which means “rock).

Earth:

On Earth, regolith takes the form of dirt, soil, sand, and other components that are formed as a result of natural weathering and biological processes. Due to a combination of erosion, alluvial deposits (i.e. moving water deposing sand), volcanic eruptions, or tectonic activity, the material is slowly ground down and laid out over solid bedrock.

central Yilgarn Craton, Western Australia.
Picture of Mt Magnet in the Central Yilgarn Craton in Western Australia, which dates to the Precambrian Era. Credit: geomorphologie.revues.org

It can be made up of clays, silicates, various minerals, groundwater, and organic molecules. Regolith on Earth can vary from being essentially absent to being hundreds of meters thick. Its can also be very young (in the form of ash, alluvium, or lava rock that was just deposited) to hundreds of millions of years old (regolith dating to the Precambrian age occurs in parts of Australia).

On Earth, the presence of regolith is one of the important factors for most life, since few plants can grow on or within solid rock and animals would be unable to burrow or build shelter without loose material. Regolith is also important for human beings since it has been used since the dawn of civilization (in the form of mud bricks, concrete and ceramics) to build houses, roads, and other civil works.

The difference in terminology between “soil” (aka. dirt, mud, etc.) and “sand” is the presence of organic materials. In the former, it exists in abundance, and is what separates regolith on Earth from most other terrestrial environments in our Solar System.

The Moon:

The surface of the Moon is covered with a fine powdery material that scientists refer to it as “lunar regolith”. Nearly the entire lunar surface is covered with regolith, and bedrock is only visible on the walls of very steep craters.

Earth viewed from the Moon by the Apollo 11 spacecraft. Credit: NASA
Earth viewed from the Moon by the Apollo 11 spacecraft, across a sea of lunar soil. Credit: NASA

The Moon regolith was formed over billions of years by constant meteorite impacts on the surface of the Moon. Scientists estimate that the lunar regolith extends down 4-5 meters in some places, and even as deep as 15 meters in the older highland areas.

When the plans were put together for the Apollo missions, some scientists were concerned that the lunar regolith would be too light and powdery to support the weight of the lunar lander. Instead of landing on the surface, they were worried that the lander would just sink down into it like a snowbank.

However, landings performed by robotic Surveyor spacecraft showed that the lunar soil was firm enough to support a spacecraft, and astronauts later explained that the surface of the Moon felt very firm beneath their feet. During the Apollo landings, the astronauts often found it necessary to use a hammer to drive a core sampling tool into it.

Once astronauts reached the surface, they reported that the fine moon dust stuck to their spacesuits and then dusted the inside of the lunar lander. The astronauts also claimed that it got into their eyes, making them red; and worse, even got into their lungs, giving them coughs. Lunar dust is very abrasive, and has been noted for its ability to wear down spacesuits and electronics.

Alan Bean Takes Lunar Soil Sample
Alan Bean takes a sample of lunar regolith during the Apollo 12 mission. Credit: NASA

The reason for this is because lunar regolith is sharp and jagged. This is due to the fact that the Moon has no atmosphere or flowing water on it, and hence no natural weathering process. When the micro-meteoroids slammed into the surface and created all the particles, there was no process for wearing down its sharp edges.

The term lunar soil is often used interchangeably with “lunar regolith”, but some have argued that the term “soil” is not correct because it is defined as having organic content. However, standard usage among lunar scientists tends to ignore that distinction. “Lunar dust” is also used, but mainly to refer to even finer materials than lunar soil.

As NASA is working on plans to send humans back to the Moon in the coming years, researchers are working to learn the best ways to work with the lunar regolith. Future colonists could mine minerals, water, and even oxygen out of the lunar soil, and use it to manufacture bases with as well.

Mars:

Landers and rovers that have been sent to Mars by NASA, the Russians and the ESA have returned many interesting photographs, showing a landscape that is covered with vast expanses of sand and dust, as well as rocks and boulders.

A successful scoop of Martian regolith (NASA/JPL-Caltech/University of Arizona/Max Planck Institute)
A successful scoop of Martian regolith performed by NASA’s Phoenix lander. Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute

Compared to lunar regolith, Mars dust is very fine and enough remains suspended in the atmosphere to give the sky a reddish hue. The dust is occasionally picked up in vast planet-wide dust storms, which are quite slow due to the very low density of the atmosphere.

The reason why Martian regolith is so much finer than that found on the Moon is attributed to the flowing water and river valleys that once covered its surface. Mars researchers are currently studying whether or not martian regolith is still being shaped in the present epoch as well.

It is believed that large quantities of water and carbon dioxide ices remain frozen within the regolith, which would be of use if and when manned missions (and even colonization efforts) take place in the coming decades.

Mars moon of Deimos is also covered by a layer of regolith that is estimated to be 50 meters (160 feet) thick. Images provided by the Viking 2 orbiter confirmed its presence from a height of 30 km (19 miles) above the moon’s surface.

Asteroids and Outer Solar System:

The only other planet in our Solar System that is known to have regolith is Titan, Saturn’s largest moon. The surface is known for its extensive fields of dunes, though the precise origin of them are not known. Some scientists have suggested that they may be small fragments of water ice eroded by Titan’s liquid methane, or possibly particulate organic matter that formed in Titan’s atmosphere and rained down on the surface.

Another possibility is that a series of powerful wind reversals, which occur twice during a single Saturn year (30 Earth years), are responsible for forming these dunes, which measure several hundred meters high and stretch across hundreds of kilometers.  Currently, Earth scientists are still not certain what Titan’s regolith is composed of.

Data returned by the Huygens Probe’s penetrometer indicated that the surface may be clay-like, but long-term analysis of the data has suggested that it may be composed of sand-like ice grains.  The images taken by the probe upon landing on the moon’s surface show a flat plain covered in rounded pebbles, which may be made of water ice, and suggest the action of moving fluids on them.

Asteroids have been observed to have regolith on their surfaces as well. These are the result of meteoriod impacts that have taken place over the course of millions of years, pulverizing their surfaces and creating dust and tiny particles that are carried within the craters.

False color picture of Eros' 5.3-kilometer (3.3-mile) surface crater, showing regolith inside. Credit: NASA/JPL/JHUAPL
False color picture taken by NASA’s NEAR Shoemaker camera of Eros’ 5.3-kilometer (3.3-mile) surface crater, showing the presence of regolith inside. Credit: NASA/JPL/JHUAPL

NASA’s NEAR Shoemaker spacecraft produced evidence of regolith on the surface of the asteroid 433 Eros, which remains the best images of asteroid regolith to date. Additional evidence has been provided by JAXA’s Hayabusa mission, which returned clear images of regolith on an asteroid that was thought to be too small to hold onto it.

Images provided by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras on board the Rosetta Spacecraft confirmed that the asteroid 21 Lutetia has a layer of regolith near its north pole, which was seen to flow in major landslides associated with variations in the asteriod’s albedo.

To break it down succinctly, wherever there is rock, there is likely to be regolith. Whether it is the product of wind or flowing water, or the presence of meteors impacting the surface, good old fashioned “dirt” can be found just about anywhere in our Solar System; and most likely, in the universe beyond…

We’ve done several articles about the Moon’s regolith here on Universe Today. Here’s a way astronauts might be able to extract water from lunar regolith with simple kitchen appliances, and an article about NASA’s search for a lunar digger.

Want to buy some lunar regolith simulant? Here’s a site that lets you buy it. Do you want to be a Moon miner? There’s lots of good metal in that lunar regolith.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Reference:
NASA

You Could Fit All the Planets Between the Earth and the Moon

You could fit all the planets within the average distance to the Moon.

I ran into this intriguing infographic over on Reddit that claimed that you could fit all the planets of the Solar System within the average distance between the Earth and the Moon.

I’d honestly never heard this stat before, and it’s pretty amazing how well they tightly fit together.

But I thought it would be a good idea to doublecheck the math, just to be absolutely certain. I pulled my numbers from NASA’s Solar System Fact Sheets, and they’re a little different from the original infographic, but close enough that the comparison is still valid.

Planet Average Diameter (km)
Mercury 4,879
Venus 12,104
Mars 6,771
Jupiter 139,822
Saturn 116,464
Uranus 50,724
Neptune 49,244
Total 380,008

The average distance from the Earth to the Moon is 384,400 km. And check it out, that leaves us with 4,392 km to spare.

So what could we do with the rest of that distance? Well, we could obviously fit Pluto into that slot. It’s around 2,300 km across. Which leaves us about 2,092 km to play with. We could fit one more dwarf planet in there (not Eris though, too big).

The amazing Wolfram-Alpha can make this calculation for you automatically: total diameter of the planets. Although, this includes the diameter of Earth too.

A nod to CapnTrip on Reddit for posting this.

Moon Rotation

Moon Rotation

The rotation of the Moon is a strange situation. It takes the same amount of time for the Moon to complete a full orbit around the Earth as it takes for it to complete one rotation on its axis. In other words, the Moon rotation time is 27.3 days, just the same as its orbital time: 27.3 days.

What this means to us here on Earth is that the Moon always presents the same face to the Earth. We only see one side of the Moon, and not the other. And if you could stand on the surface of the Moon, the Earth would appear to just hang in the sky, not moving anywhere.

Astronomers say that the Moon is tidally locked to the Earth. At some point in the past, it did have a different rotation rate from its orbital period. But slight differences in the shape of the Moon caused the Moon to experience different amounts of gravity depending on its position. These differences acted as a brake, slowing the Moon rotation speed down until it matched its orbital period. There are other tidally locked moons in the Solar System. Pluto and its moon Charon are tidally locked to each other, so they always present the same face to one another.

We’ve written many articles about rotation for Universe Today. Here’s an article about the rotation of the Earth, and here’s an article about the rotation of Saturn.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also recorded an episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.

Blood Moon



A blood moon is the first full moon after a harvest moon, which is the full moon closest to the fall equinox. Another name for a blood moon is a hunter’s moon.

Before the advent of electricity, farmers used the light of the full moons to get work done. The harvest moon was a time they could dedicate to bringing in their fall harvest. And so a month later is the blood moon, or the hunter’s moon. This was a good time for hunters to shoot migrating birds in Europe, or track prey at night to stockpile food for Winter.

A full moon occurs every 29.5 days, so a blood moon occurs about a month after the harvest moon. A blood moon is just a regular full moon. It doesn’t appear any brighter or redder than any other full moon. The distance between the Earth and the Moon can change over the course of the month. When the moon is at its closest, a full moon can appear 10% larger and 30% brighter than when it’s further away from the Earth.

A blood moon will actually turn red when it matches up with a lunar eclipse. These occur about twice a year, so blood moons match up with lunar eclipses about every 6 years or so. At the time of this writing, the next blood moon lunar eclipse will be in 2015.

We’ve written many articles about the Moon for Universe Today. Here’s an article about the discovery of water on the Moon, and here’s an article about a lava tube on the Moon.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also done several episodes of Astronomy Cast about the Moon. Here’s a good one, Episode 17: Where Does the Moon Come From?

What is a Waning Moon?

Human beings have been observing the Moon for as long as they have walked the Earth. Throughout recorded and pre-recorded history, they have paid close attention to its phases and accorded them particular significance. This has played a major role in shaping the mythological and astrological traditions of every known culture.

With the birth of astronomy as a scientific discipline, how the Moon appears in the night sky (and sometimes during the day) has also gone long way towards helping us to understand how our Solar System works. It all comes down to the Lunar Cycle, the two key parts of this cycle involve the “waxing and waning” of the Moon. But what exactly does this mean?-day

Lunar Cycle:

First, we need to consider the orbital parameters of the Earth’s only satellite. For starters, since the Moon orbits Earth, and Earth orbits the Sun, the Moon is always half illuminated by the latter. But from our perspective here on Earth, which part of the Moon is illuminated – and the amount to which it is illuminated – changes over time.

When the Sun, the Moon and Earth are perfectly lined up, the angle between the Sun and the Moon is 0-degrees. At this point, the side of the Moon facing the Sun is fully illuminated, and the side facing the Earth is enshrouded in darkness. We call this a New Moon.

After this, the phase of the Moon changes, because the angle between the Moon and the Sun is increasing from our perspective. A week after a New Moon, and the Moon and Sun are separated by 90-degrees, which effects what we will see. And then, when the Moon and Sun are on opposite sides of the Earth, they’re at 180-degrees – which corresponds to a Full Moon.

Waxing vs. Waning:

The period in which a Moon will go from a New Moon to a Full Moon and back again is known as “Lunar Month”. One of these lasts 28 days, and encompasses what are known as “waxing” and “waning” Moons. During the former period, the Moon brightens and its angle relative to the Sun and Earth increases.

Synthetic view of the waxing Moon as viewed from Earth on 2013-10-15 17:00:00 UTC [NASA/GSFC/Arizona State University].
Synthetic view of the waxing Moon as viewed from Earth on 2013-10-15 17:00:00 UTC. Credit: NASA/GSFC/Arizona State University
When the Moon starts to decrease its angle again, going from 180-degrees back down to 0-degrees, astronomers say that it’s a waning moon. In other words, when the Moon is waning, it will have less and less illumination every night until it’s a New Moon.

Waning Phases:

When the Moon is no longer full, but it hasn’t reached a quarter moon – i.e. when it’s half illuminated from our perspective – we say that it’s a Waning Gibbous Moon. This is the exact reverse of a Waxing Gibbous Moon, when the Moon is increasing in brightness from a New Moon to a Full Moon.

This is followed by a Third Quarter (or last quarter) Moon. During this period, 50% of the Moon’s disc will be illuminated (left side in the northern hemisphere, and the right in the southern), which is the opposite of how it would appear during a First Quarter. These phases are often referred to as a “Half Moon”, since half the disc is illuminated at the time.

The moon in its waning gibbous phase on Sept. 12, 2014. Photo taken with a Canon 700D attached to a Maksutov 127mm telescope. Credit: Sarah&Simon Fisher
The moon in its waning gibbous phase on Sept. 12, 2014. Photo taken with a Canon 700D attached to a Maksutov 127mm telescope. Credit: Sarah&Simon Fisher

Finally, a Waning Crescent is when the Moon appears as a sliver in the night sky, where between 49–1% of one side is illuminated after a Full Moon (again, left in the northern hemisphere, right in the southern). This is the opposite of a Waxing Crescent, when 1-49% of the other wide is illuminated before it reaches a Full Moon.

Even today, thousands of years later, human beings still look up at the Moon and are inspired by what they see. Not only have we explored Earth’s only satellite with robotic missions, but even crewed missions have been there and taken samples directly from the surface. And yet, it still possesses enough mystery to keep us inspired and guessing.

We have written many interesting articles about the Moon here at Universe Today. Here’s What is the Moon’s Real Name?, Does the Moon Have Different Names?, What are the Phases of the Moon?, Is the Moon a Planet?, What is the Distance to the Moon?, and Who Were the First Men on the Moon?

Want to know when the next waning gibbous moon is going to happen? NASA has a list of moon phases for a period of 6000 years.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Sources: