# Meteors made of differing substances. Will they all burn up?

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If an object enters Earth's atmosphere, what determines whether it burns up or not?

Example

A feather is released from a space-ship 30,000 km away from Earth and falls under the influence of Earth's gravity.

Will it burn up on re-entry or will it float down to the surface unharmed. If it would be unharmed, where is the cutoff point for which objects survive?

I can give a partial answer to this. In general, larger objects are more likely to break up than smaller ones, and comets are more likely to break up than meteors. A feather would likely burn up too, here's why:

30,000 KM above the surface, or roughly 4.7 earth radii, the escape velocity at that height would be the square root of that or roughly 2.17 times less or 46% of the escape velocity from the surface, so a feather dropped from that height would be traveling at nearly 54% of earth's escape velocity when it hit the atmosphere, or about 6 KM per second. That's about 7 times as fast as a bullet and I'd wager, that would burn up a feather pretty quick.

Speed of space collisions is faster than free-fall velocity can reach cause anything that hits the earth from space is also in free fall and you can add to that any relative velocity between the objects. The slowest meteors hit the earth at about 11 KM per second, not surprisingly, the Earth's escape velocity.

http://www.amsmeteors.org/fireballs/faqf/#12

Now, if you drop a feather from the highest hot air balloon, then it probably would float down to the earth, accelerating faster at first in the thinner atmosphere, then more slowly as the air got thicker.

Small point to add, angle of approach matters too. A glancing blow and the object can effectively bounce off the atmosphere, not burn up in it.

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Today Phil helps keep you from ticking off an astronomer in your life by making sure you know the difference between a meteor, meteorite, and meteoroid. When the Earth plows through the stream emitted by a comet we get a meteor shower. Meteors burn up about 100 km above the Earth, but some survive to hit the ground. Most of these meteorites are rocky, some are metallic, and a few are a mix of the two. Very big meteorites can be a very big problem, but there are plans in the works to prevent us from going the way of the dinosaurs.

What Meteors Are 0:59
Meteor Shower 4:22
What Meteors Are Made Of 7:10
Very Big Meteorites Can Be a Very Big Problem 8:36

PHOTOS/VIDEOS
Shooting star http://dakotalapse.com/wp-content/uploads/2013/02/IMG_5555-reboot1.jpg [credit: Randy Halverson / Dakotalapse.com]
Cosmic Fireball Falling Over ALMA http://www.eso.org/public/usa/images/potw1414a/ [credit: ESO / Christoph Malin]
Meteor light https://sphotos-b.xx.fbcdn.net/hphotos-ash3/704204_406950402710734_1157020008_o.jpg [credit: Randy Halverson / Dakotalapse.com]
Bolide 10/16/14 https://www.youtube.com/watch?v=GZXqmPhd8AQ [credit: reddit user -545-]
Meteor Video http://svs.gsfc.nasa.gov/vis/a010000/a010700/a010747/10747_Swift_Asteroid_H264_Good_1280x720_29.97.mov [credit: NASA/Goddard Space Flight Center]
Orbit Video http://svs.gsfc.nasa.gov/vis/a000000/a004100/a004159/209PLINEAR-swingAround.slate.HD1080.mp4 [credit: NASA's Scientific Visualization Studio]
When Gemini Sends Stars to Paranal http://twanight.org/newTWAN/photos.asp?ID=3003955 [credit: Stephane Guisard]
Perseid below space station http://apod.nasa.gov/apod/image/1208/iss028e024847perseid.jpg [credit: NASA]
Geminids shower http://www.slate.com/blogs/bad_astronomy/2014/12/15/geminids_meteor_shower_photo.html [credit: Neil Zeller]
Stony meteorite http://en.wikipedia.org/wiki/File:AllendeMeteorite.jpg [credit: Wikimedia Commons, H. Raab]
Iron meteorite http://commons.wikimedia.org/wiki/File:Nickel-iron_meteorite_fragment,_5.5_billion_years_old,_found_near_Flagstaff_AZ_-_Franklin_Institute_-_DSC06707.JPG [credit: Wikimedia Commons, Daderot]
Stony iron meteorite http://en.wikipedia.org/wiki/Pallasite#/media/File:Bernham_meteorite_sept_2010.JPG [credit: Wikimedia Commons, Supportstorm]
Chondrites http://commons.wikimedia.org/wiki/File:Allende_meteorite,_carbonaceous_chondrite_(14787764392).jpg [credit: Wikimedia Commons, James St. John]
Pallasite https://www.flickr.com/photos/jsjgeology/14608975850/ [credit: James St. John]
Aftermath of Chelyabinsk Meteor https://www.youtube.com/watch?v=Q9KwK0izt5c [credit: NASA]
Near-Earth asteroid 2013 https://www.youtube.com/watch?v=RmPsQdEHyPU [credit: Gianluca Masi, permission granted by author]
Dinosaur drawing courtesy of Zach Weiner of Saturday Morning Breakfast Cereal http://www.smbc-comics.com/?id=1535

I love astronomy. You may have noticed. But there's one really frustrating aspect of it: Everything we study is really far away. Nearly everything we understand about the universe comes from light emitted or reflected by objects. I'd be nice if we could get actual samples from it. Physical specimens we could examine in the lab.

Well, sometimes the universe can be accommodating and allows us to hold it in our hands. Cambot, can we get this up on still store?

If you go outside on a clear, dark, moonless night, and you really should, chances are pretty good that within a few minutes, you'll see a shooting star. It'll zip across the sky, a fiery dot leaving a long glowing trail behind it. They're one of the most exciting and fun things you'll see when you look up, and they always get a gasp and a squeal of delight from someone who's stargazing. What you're actually seeing is a tiny bit of interplanetary debris: rock, ice, or metal ramming through the Earth's atmosphere, heated to incandescence. Most are faint, but some can be astonishingly bright. I saw one once that left an afterimage on my eye. Obviously shooting stars aren't really stars, so what do we call them?

Sometimes it seems like astronomers use different names for objects to keep things as confusing as possible, but really we do that to separate out different things. In this case, the actual bit of solid stuff coming from space is called a meteoroid. The phenomenon of the meteoroid getting hot and blazing across the sky is called a meteor, and finally, if it hits the ground, we call it a meteorite. I think the second best way to tick off an astronomer is to mix up meteor and meteorite. Sometimes astronomers can be pretty pedantic about such things. Oh, the best way to tick off an astronomer? Ask 'em, "Hey, what's your sign?"

Amazingly, a typical meteor that you'll see is due to a meteoroid that's tiny, probably smaller than a grain of sand. How can that be? It's because they're hauling mass. You heard me. The meteoroid is orbiting the Sun, probably at speeds of a few dozen kilometers per second. As it approaches the Earth, our planet's gravity accelerates it an additional 11 kilometers per second, Earth's escape velocity. And when it enters our atmosphere, it's moving incredibly fast, up to 70 kilometers per second or more. The energy of motion is called kinetic energy. If you wanna get something moving, you have to give it energy, and if you want it to stop, you have to take that energy away. This kinetic energy depends on the mass of the object and how fast it's moving. In fact, it depends on the square of the velocity, double its speed, and it'll have four times the kinetic energy. Meteoroids may usually be small, but they're screaming fast and have a huge amount of kinetic energy. As they hit our atmosphere, they slow from their ridiculous orbital speed to nearly a standstill, and all that energy has to go somewhere. It gets converted into light and heat, and that's what we see as a meteor.

A big misconception about meteors is that they got hot due to friction with air. Actually, a far bigger contributor to their heat is compression. One of the most basic laws of physics is that when you compress a gas, it heats up, and a meteoroid coming in at hypersonic speeds compresses the air in front of it a lot, heating it hugely. The gas can reach temperatures of thousands of degrees Celsius for a few seconds. The air radiates away this heat, in turn heating up the meteoroid. The material on the surface vaporizes and blows away, a process called ablation. That ablated material leaves a glowing trail behind the meteor, which we call a train. Sometimes it can glow for several minutes, getting twisted up in high altitude winds, leaving behind an eerie ghost-like persistent train. This all happens high above your head, about 90 to a hundred kilometers above the ground.

Typically, from any one location, you can see a few meteors per hour. It may not seem like much, but when you add them up all over the planet, you find the Earth is getting pelted to the tune of about a hundred tons of material a day. But again, most of these meteoroids are teeny tiny. Those random meteors are called sporadic meteors. They tend to be rocky in composition and generally come from asteroids. If two asteroids smack into each other, the collision can eject little bits of material that then orbit the sun on their own. If their orbit crosses the Earth, then you have a potential meteor. It may take a few million years, but at some point the Earth and the meteorite are at the same place at the same time, and boom.

But sometimes, meteoroids travel in packs. When that happens, we can get meteor showers, many dozens or even hundreds of meteors per hour. With one exception: those don't come from asteroids. They come from comets. When a comet orbits the sun, the ice on it turns to gas, dislodging dust and gravel mixed in. This material leaves the comet and tends to stay more or less in the same orbit as the comet itself. Over time, that material gets scattered all along the orbit, creating a puffy ribbon of tiny pieces of space debris around the sun. When the Earth plows through that cloud of debris, we get a meteor shower.

From our viewpoint on Earth, we see meteors shooting across the sky, apparently radiating away from a single point. That's a perspective effect. It's like driving through a tunnel and seeing the tiles on the wall and ceiling flying past you, all apparently coming from a point ahead of you. The point on the sky where the meteors come from is called the radiant, and the shower is named after the constellation the radiant's in.

So we have the Perseid meteor shower, the Leonids, the Camelopardalids, or the Camelopardalids, and since the Earth hits a specific comet stream around the same time every year, the showers are annual. The Perseids are in August and the Leonids in November. Watching a meteor shower is easy. Just go outside and look up. Generally, they're better after local midnight. The Earth plows into the meteoroids, so facing the direction of Earth's orbital motion means more meteors, just like you get more raindrops on the front windshield of your car than on the back when you're driving through a storm. After local midnight, you're on the part of the Earth facing into the orbit, so you see more meteors. By the way, if you happen to be on the International Space Station, you have to look down to see a meteor. In 2011, astronaut Ron Garan photographed a Perseid burning up below him, but don't worry, the odds of the Space Station getting hit are extremely low. Space is big.

Oh, and that one exception that I mentioned before? That's the annual Geminid shower, which occurs in December. That comes from the asteroid 3200 phaethon, which is on an orbit that takes it very close to the Sun. It's possible it gets so hot that the rock vaporizes, making it act like a comet.

The vast majority of meteorites are small and tend to burn up in our atmosphere, but they can be bigger. A bolide or fireball is an extremely bright meteor, and those can be about the size of a grapefruit. Those happen pretty often somewhere over the Earth. I've seen a few myself. Very rarely, an incoming meteoroid will survive all the way to the ground and become a meteorite. Sometimes, the immense pressure of ramming Earth's air causes the incoming meteoroid to crumble or even explode, raining down dozens or hundreds of smaller pieces. Typically, they slow rapidly after their blaze of glory and simply fall the rest of the way to the ground. The air up there is cold, and their interiors are cold from being in space so long. So despite what you might think, meteorites don't cause fires when they hit the ground. In fact, they can be quite chilly.

Meteorites are classified into three broad categories: stony, which are mostly rock, iron, which are mostly metal, and stony iron, which are a mixture of the two. The majority of meteorites we find are stony. The stony meteorites are themselves subdivided into two kinds: chondrites and achondrites.

Chondrites contain chondrules, small grains of minerals. These are very primitive and are thought to have condensed out of the original disk of material that formed in the solar system. Their ages can be found by looking at ratios of elements in them formed from radioactive decay. The oldest known meteorite formed 4.568 billion years ago: before the Earth itself formed.

Achondrites don't have chondrules in them. Most likely they came from a bigger asteroid, one that was once molten all the way through, mixing the minerals. A big collision disrupted the parent body, creating the achondritic meteorites. Iron meteorites most likely come from the center of a large asteroid, one big enough that metals fell to the center via gravity. Again, a big impact blew the asteroid up, scattering its material around the asteroid belt, and with some on orbits that eventually intersected Earth's.

Stony irons are the rarest. Some have green or orange crystals of a mineral called olivine embedded in a web of metal. Called pallasites, they might be the most beautiful of all meteorites. I actually collect meteorites. It's fun but can be a somewhat pricey hobby. If you're interested, make sure you get them from a licensed dealer, we have links to some in the doobly-doo.

Of course, on occasion, the meteorite coming in can be a tad bigger, and when that happens, well, all hell can break loose. On February 15th, 2013, residents of the Russian city of Chelyabinsk got a rude awakening. At 9:20 AM local time, a rock about 19 meters across came in at a low angle. It got nearly as bright as the sun as it slammed into the atmosphere, and the pressure of its passage broke it up into several chunks, which broke up again. In a moment's time, the sudden energy released was equivalent to the detonation of a half million tons of TNT, as much as a small atomic bomb.

While no one was killed, over 1,000 people were injured by flying glass, shattered by the explosion. No doubt they were at their windows, gawking at the huge vapor trail in the sky when the shock wave hit. There was no warning for this event. The asteroid was essentially too small to detect while it was out in space. Well, for now at least.

Telescopes are coming online soon that should be able to find smaller asteroids, and give us some warning. Astronomers are more worried about ones roughly 100 meters across or bigger. These can do serious damage on a city-wide scale, or larger, but at the moment aren't easy to spot much in advance. And what to we do if we do see one headed our way?

As of right now, there's not much we can do. Studies have been done to determine the best course of action, maybe lobbing a nuke at it or simply ramming it with a space probe to change the orbit and make sure it misses Earth. These ideas look good on paper, but they haven't been tested yet, we're still a few years from that. The good news is that objects that size hitting the Earth are rare, maybe once every century or three, but if we do nothing, it will happen eventually. As science fiction writer Larry Niven points out, "Dinosaurs went extinct because they didn't have a space program," hopefully, we're smarter than they were.

Today you learned that meteors are small bits of interplanetary debris sloughed off by asteroids and comets. When the Earth plows through the stream emitted by a comet, we get a meteor shower. Meteors burn up about 100 kilometers above the Earth, but some survive to hit the ground. Most of these meteorites are rocky, some are metallic, and a few are a mix of the two. Very big meteorites can be a very big problem, but there are plans in the works to prevent us from going the way of the dinosaurs.

Crash Course Astronomy-- hey, Crash Course, meteors, cool. Crash Course Astronomy is produced in association with PBS Digital Studios. Head over to their channel for even more awesome videos. This episode was written by me, Phil Plait. The script was edited by Blake de Pastino, and our consultant was Dr. Michelle Thaller. It was directed by Nicholas Jenkins, the script supervisor and editor is Nicole Sweeney, and sound designer is Michael Aranda, and the graphics team is Thought Cafe.

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## Comets, meteors and asteroids

What's the difference between comets, meteors and asteroids?

What are comets, meteors, shooting stars, meteorites and asteroids made of? And what is the difference between them all?

Comets, meteors, meteorites and asteroids include some of the smallest interplanetary objects astronomy is concerned with but they are among the most spectacular and the only ones we are likely to come into contact with before space travel becomes common!

Whether you are wishing on a ‘shooting star’ or wondering about the likelihood of an asteroid ending life on earth, keep your eyes on the skies for these objects.

### What’s a comet?

Generally speaking, a comet is a frozen ball (of water, carbon dioxide, ammonia and other organic carbon compound ices) hurtling through space. As these substances stream off the comet they form a spectacular gas and dust cloud of enormous length that can often be seen from earth with the naked eye.

### Meteors and meteorites

A meteor is a piece of space debris that burns up as it enters the earth’s atmosphere creating a ‘shooting star’. Certain times of the year are known for spectacular displays and these are generally associated with comets that have passed by after spewing fragments in their wake.

Occasionally, a larger fragment will fail to burn up completely and when it hits the ground it is called a meteorite.

### Asteroids and minor planets

Asteroids range greatly in size with some approaching the size of small planets. The largest asteroid is Ceres, it is 1003 km in diameter. Pallas and Vesta (the only asteroid at all visible to the naked eye) have diameters of about 500 km and 30 more asteroids have diameters greater than 200 km. Most asteroids, however, are small objects only a few kilometres across.

The compositions of asteroids are very similar to those of meteorites and this has led to the idea that meteorites originated in the asteroid belt.

As large as the tail of a comet is, it is very, very thin. It is not much more a vacuum, so a typical comet doesn't lose a large percentage of its mass as it passes perhelion.

For example, Comet Halley at its closest approach to the Sun loses about 30,000,000 grams of water a sec. This seems like a lot, but it only adds up to a loss of a 1 meter depth of its surface per orbit. Since Comet Halley is over 5 km in radius, a loss at this rate would have Halley totally evaporated in about 1700 orbits or in something over 13,000 yrs.

Comets do eventually melt away and this happens faster for the short term comets. The dust trails they leave behind in their orbit are called comet remnants. From time to time, the Earth passes through these remnants and we get meteor showers. Two of the more familiar ones are the Perseids and Leonids, which occur annually.

Thanx for the info. I didn't know comets were that big and had that much water/ice on them. out of interest, why don't any meteorites have tails of ice? they're made of the same stuff are they not?

it says (in brief):
The first examination of the dust particles collected from the tail of a comet, which were collected by the Nasa probe on a 2.8bn-mile (4.6bn-kilometre) round trip to comet Wild 2, has revealed minerals that could only have formed at blistering temperatures close to the sun. The finding has surprised mission scientists as comets are known to form in the frigid outer reaches of the solar system, at least 40 times further away from the sun than the Earth is.
"The interesting thing is we are finding these high-temperature minerals in materials from the coldest place in the solar system," said Donald Brownlee, the project's Washington University-based lead scientist. "It's certain these materials never formed inside this icy, cold body."

any ideas of how blistering temperatures close to that of the sun can be seen on a dead ball of ice?

and i also found an interesting paper on 'Spectroscopic Proof of the Repulsion by the Sun of Gaseous Molecules in the Tail of Halley's Comet' which looks into detail at the strong repulsive effect the sun has on the particles left after comets, and specifically looks at the tail of Halley's comet that you mentioned.
http://links.jstor.org/sici?sici=0003-049X(191105/08)50:199<254:SPOTRB>2.0.CO2-Z this effect was predicted by plasma cosmology, and i think it may be a good indication that they were correct about the electrical nature of comets tails, which would also explain the high temparatures observed by the Nasa probe.

are there any pictures that NASA has taken of close up images of the water and ice vaporizing from the surface of a comet that would disprove that theory? i would like to see them. They claim comets are ionizing particles in the 'ion wind' and are charged bodies moving through a varying electric field produced by the sun, and thats the sole cause of the tail. Im not sure which is more plausible but both seem good explanations, the tails do look electrical in nature sometimes and their brightness is known to vary greatly.

## What is a “Falling Star”?

A Falling Star is simply an ancient term used to describe what appears as a long and fast streak of light across the sky, sometimes with an explosion or fireball. Although they may resemble distant actual stars in the background of the night sky, these are in fact what’s scientifically called a meteor. A meteoroid on the other hand, is a small body that enters Earth’s atmosphere while an asteroid and comet are larger bodies that can sometimes enter Earth’s atmosphere. When one of these objects gets close enough to Earth and within the layers of our atmosphere as already mentioned, friction then causes the object to break and burn up as it approaches Earth’s surface at speeds of around 40,000 to 70,000 mph. Because of its trajectory and speed, particles of the object leave trails for long distances behind it that can extend for hundreds of miles across the celestial sky. Oh and by the way, if the object does not completely obliterate on it’s journey through Earth’s atmosphere and some leftover fragment manages to make contact with the ground, then this leftover piece is commonly referred to as a meteorite at that point.

A meteoroid is defined as an object smaller than 1 meter in size but not smaller than 1 millimeter. At that point it’s considered cosmic dust. Meteoroids are often fragments of asteroids and comets. However, an asteroid is defined as an object larger than 1 meter in space and is made up of mostly rock, iron and nickel. While a comet is more defined as a chunk of dust and ice and sometimes comets and asteroids can be the same size, but again have different formation structure materials.

A star however, is a different beast all in itself and has a mass of over a million times that of Earth. Our host star we call the Sun could fit 1.3 million Earths inside of it for a comparison. So as you can clearly see, there are no actual stars falling into Earth or you and me and everyone else would not be around to talk about them. Furthermore, larger objects don’t technically fall into smaller objects. Instead, it’s exactly the opposite.

### Where do Meteors come from?

Now that you know that no stars actually fall into Earth, then you’re probably also wondering where in the world do meteors come from? Well I can assure you that they don’t come from anywhere of this world Earth that is. However, they are our planetesimal neighbors. Wait, what? What exactly is a planetesimal first off? A planetesimal is basically a failed protoplanet. I know, I know! So many things to understand in order to get to the point. Stay with me though this will all make sense as you read on.

When the solar system was just a bunch of gas and dust clouds floating along in space, essentially everything started to collapse into shape at this time around 4.6 billion years ago. Hydrogen and Helium formed together relatively quickly and started to craft the Sun as the other bodies in this nebula also started to develop simultaneously. Some objects clumped together faster than others and as the Sun began to generate and emit radiation and generate a huge gravitational field at the same time, the smaller formations were then cleaning out their orbital neighborhoods of what the sun left them as scraps to fight over. It is said that at one time we may have had up to 20 planets in our young solar system, but that’s another article for another day. For now, let’s stay focused on what’s going on with the solar system’s early formation days.

### What are Planetesimals and Protoplanets?

In a time of just 10-20 million initial years, most of the planets already took their shapes and sizes as we know today. The terrestrial–or rocky–planets were the closest to the Sun and include Mercury, Venus, Earth and Mars. The next region of space if just a swirling disc of planetesimals and protoplanets, but you probably know them better as meteoroids and asteroids. These are embryo-like planet formations that just couldn’t quite get enough mass to form into a more defined planet. Oh and you can challenge your friends by telling them that asteroids are also referred to as minor planets.

A protoplanet is the next step up from those tiny planetesimals that we call asteroids and has to be at least 1 kilometer in size. A protoplanet is a planet 1 km in size and can be of any size above that. However, once protoplanets get big enough to take on more of a spherical shape, orbit the sun, but still can’t quite clear their neighborhood of debris, it may then be referred to as a dwarf planet.

### The Asteroid Belt

Okay so remember where we’re at? Mercury, Venus, Earth, Mars, Asteroid Belt, then come the Jovian (Gas Giant) Planets. In the following order you have Jupiter, Saturn, Uranus and finally Neptune. Jupiter is the largest planet in our solar system as you probably already knew from early education as a child. But did you know that Jupiter is likely the reason there’s an asteroid belt in between Mars and Jupiter itself? Jupiter’s gravitational field is so strong compared to the rest of the planets that this likely disrupted the formation of Ceres from graduating from a Dwarf Planet into one that we could actually call a real planet. Ceres is considered a protoplanet, dwarf planet and an asteroid. It’s actually the largest asteroid in the asteroid belt. I didn’t mention Ceres until now because there are moons bigger and smaller than this object. Big enough to be a moon, yet orbits no planet so classified as a dwarf planet instead…barely.

The Asteroid Belt is a region of space that occupies the area between Mars and Jupiter and contains many rocky, iron, nickel objects.

This asteroid belt, in between Mars and Jupiter, is where some of the asteroids and meteoroids that eventually hit Earth come from. These are called Near Earth Objects or NEOs once they come within a defined certain distance. Sometimes these rocky/iron/nickel mixed asteroids get gravitationally bumped out of their orbits and pushed into Earth’s orbit for a fantastic collision. These rarely make contact with Earth in case you were wondering so no need to stock up on doomsday supplies just yet. In fact, it’s so rare of collisions that we just call these sporadic meteors when they actually come in contact with Earth because they are not what you usually see during a meteor shower. We’ll get to where meteor showers come from in a moment, but first a quick word from our sponsors…..just kidding. No commercials for this literature podcast, although you may eventually see side ads to help this student writer pay for his time on these fantastic–average–articles that everyone𔃀 or 3 people–is/are talking about.

### What are Meteoroids, Meteors and Meteorites?

Anyways, you perhaps already figured out something interesting so far. Although wandering meteoroids and asteroids later hit Earth’s atmosphere and become a Meteor, most of them will usually completely burn up. However, the iron asteroids are the objects that have the highest potential to leave their Meteorite fragments on the ground for people like you and me to stumble upon easily either by trained eyesight or with the aide of a metal detector. Comets, Asteroids and Meteoroids are technically classified as different objects based on their size and composition right up until the enter Earth’s atmosphere. It’s at this point they are all technically referred to as a Meteor and if any fragments remain intact when they reach the surface, they are then known as a meteorite.

### The Kuiper Belt

Now that you know more about the objects from the nearby Asteroids Belt, lets delve further into space right up Uranus axis towards Neptune and beyond. This leaves us near Pluto, the bullied little guy who just couldn’t quite make the Solar System softball team as a real planet. Since the 1970’s it’s been discussed by scientists around the world if Pluto should be reclassified into something else due to its smaller size as discovered with newer technology and methods since it was first discovered. Several years later on January 5, 2005 a new further object was discovered that we named Eris which is the Greek goddess of strife and discord and would soon display an example of that at her discovery. Measurements of Eris revealed that it’s actually 27% more massive than Pluto which caused a dilemma. Eris was quickly named the 10th planet by NASA until International Astronomical Union (IAU) stepped in and said, “Whoa whoa whoa, wait a minute, let’s actually define what a planet really is.” or something like that. So by August of 2006, Planets would then be discerned as a new term called Dwarf Planets with clear definitions. Dwarf planets are protoplanet-mass objects in space that do not clean out their orbital neighborhood and also do not revolve around other planetary objects. R.I.P. Pluto 1930 – 2006. Pluto got demoted to a Dwarf Planet and the Solar System suddenly only has 8 planets after the history books were already written. Thanks a lot Eris, goddess of strife and discord! A name well lived up to.

The kuiper belt is a region of many icy-dust like objects outside the orbit of Neptune that also orbit the sun.

In this same region that Pluto orbits is where we are going next to learn about where meteor showers come from. But wait! How can Earth have showers of meteors raining down on it from a place so incredibly distant and thought of as void where no more planets call home? What is this mysterious zone that is the origin of meteor showers here on Earth, you ask? Well nothing short of what we like to call the Kuiper Belt. The kuiper belt is a region of space beyond Neptune where many comets, asteroids and other small icy objects are located.

The main difference between the Asteroid belt between Mars and Jupiter and the Kuiper belt at the outside region of the planets is heat. As you can imagine the kuiper belt is a very cold area because it is so distant from the Sun. This is where ice and dust clump together much like dirty snowballs of many shapes and sizes. Keep in mind that the comets and asteroids are all mostly the same age as the sun and other planets. Around 4.5 to 4.6 billion years old. Here’s the region of space where some of the inner comets come from as you may have guessed. However, did you know there is yet an additional, even more distant place where outer comets come from and will sometimes cross paths with Earth’s orbit.

### The Oort Cloud

Outer comets come from a place much much further than the kuiper belt. If you thought the kuiper belt was a long ways away from home, guess again. On September 5, 1977 a satellite called Voyager 1 was launched into space and sent on a one way trip into deep space. Voyager 1 finally got past the kuiper belt 35 years later on August 25, 2012 and is now considered interstellar, but that’s not technically true just yet. It still has yet another 300 years of travel to get to the beginning layer of what we call the Oort Cloud. The Oort cloud totally surrounds our disc shaped solar system in a much larger spherical shape with even colder and bigger comets. It will take Voyager 1 yet another incredible 30,000, yes 30 thousand years to get past this entire thick region of space to finally be in true outer space. However, this cloud of comets around us isn’t exactly like you think. The objects are spaced so far apart that the distance between these objects is about the same distance as the Sun and Saturn are apart. In other words, these Oort cloud objects are on average about 930 million miles apart from each other. Yet this area is so incredibly vast that it reaches half way to the next nearest star, Alpha Centauri which is 4 light years away from us. This Oort cloud is thought to have been close enough to another star in the past that the gravity of the other neighboring star is likely what bumped some of these distant comets into Earth’s direction. Another hypothesis is that there might be an actual large Planet 9 or even a binary dead star in this region. Okay so it’s likely not actually a dark binary star despite what some people speculate, but something of pretty good mass is giving us evidence that whatever it is, it has enough mass to be disrupting the outer comets in the Oort cloud and sending them our way. This incredibly distant region of space is where outer comets come from and some can be the size of large mountains.

### Meteor Showers

No matter where the icy-dust balls we call comets come from, near or far, as these objects go rogue and cross paths with Earth’s orbit, they push through space with what we call a Coma in front of them and 2 tails behind them. One tail is a gas tail while the other tail is a dust and debris tail. The coma of a comet is like the windshield of the comet that forms as it plows through space and gets nearer to the sun. It is calculated that some of these comas can reach a width of nearly 1 million miles wide and also have a tail as long as 160 million miles long. To give you an idea of how long these comet tails can be, Earth itself is at a average distance of about 93 million miles so a comet’s tail can sometimes be calculated 60 million miles longer than this distance. As you can see, comets leave a vast debris field behind them that will stay in that orbit until something crosses paths and cleans it up. Now because comets can easily be predicted and their orbital paths be tracked, therefore so can meteor showers. When Earth later crosses one of these old comet paths, the night skies light up with many meteors, hence the name meteor shower. Sometimes these meteors can be seen every couple of minutes and can last for weeks at a time.

### Halley’s Comet and the Orionid meteor shower

Halley’s comet is perhaps the most famous comet that was first discovered in 1758 by Edmond Halley who was an English Astronomer from the United Kingdom. It is a short-period comet that can be seen from Earth by the naked eye every 75-76 years. It will next pass by Earth around July 28th, 2061 for all the world to witness yet once again. Some lucky people will even live long enough to see this event happen twice in their lifetime. While its radius is only 3.4 miles, this tiny ice-ball in the sky leaves an orbital debris path behind it that makes for an amazing show in the night sky during an event we call the Orionid meteor shower. The Orionids name came from the point they appear to centrally radiate from, called the radiant, lies in the constellation Orion as seen from the northern hemisphere. This shower usually produces about 20 meteors per hour and can be seen every year from around October 2 through November 7th with peak viewing around October 20th. Although this comet itself passes by only every 75 years or so, keep in mind it’s the dust and debris remnants that can be seen annually as Earth sweeps through this leftover path year after year. The radiant (or center-point) of the Orionids is actually located between the constellations Orion and Gemini (in the south-eastern sky before dawn, as viewed from mid-northern hemispheres. Hence the name Orionid meteor shower. This is just one example of a meteor shower, but the International Astronomical Union (IAU) actually lists nearly 900 of them with 100 well understood. Remember, that’s the same Union who demoted Pluto as a Dwarf planet? Yeah, they are a very busy group over there.

### Doomsday Meteors

From movies like Armageddon to Deep Impact, Hollywood certainly knows how to scare and entertain us while leaving doomsday images in our minds for many years. Just this week, there are articles upon articles cascading out around the web about how NASA is supposedly reporting that Earth will be slammed by a 4.4 kilometer asteroid when in fact they created a “hypothetical simulation” video to demonstrate how NASA could potentially try to deflect an asteroid and what would happen if a chunk broke loose and hit Manhattan as an example. The video can be seen here and is for demonstration purposes only and was actually released in 2019, but getting mixed up with recent reports of a 4.4 km object to pass by Earth in April 2020. That is, if you consider 3.9 million miles away as actually passing by Earth.

simulation video combined with an actual real report of an asteroid to “pass by” Earth on April 29 at a distance of 3.9 million miles away. Our moon is about 240,000 miles away so if this is actually considered close to Earth, then at least it gives science fiction writers a lot to mis-articulate online.

### What size meteorite killed the dinosaurs?

Speaking of doomsday meteorites, what are the requirements and probability of a meteor like the one to have caused the dinosaurs to go extinct? The Chicxulub asteroid as it is called was estimated to be around 50 miles wide in orbit and 6 to 9 miles wide at impact. This meteorite was an asteroid or comet that blasted into Earth 66 million years ago, devastating the entire globe from immediate impact shock waves that likely circled Earth several times over and left the skies dark for many years thereafter, blocking the sun from reaching the ground long enough to cause an ice-age. How likely is this to ever happen again? Experts speculate that the dinosaur killer event is a 1 every 100 million year event.

In comparison, the Tunguska event was a 1908 meteor that exploded in mid air before making contact with the ground and flattened an estimated 80 million trees over an 830 square mile forested area. Then there’s the largest and oldest known impact crater, Vredefort Crater, located in South Africa. It is approximately 250 kilometers in diameter and is thought to to be about two billion years old. Then there’s the Barringer Crater in Arizona that although it’s not the biggest of impact craters here on Earth, it is one of the most well preserved and measures just under a mile wide. The Barringer Crater object hit about 50,000 years ago and was estimated to be just 50 meters wide.

### So what does all this mean?

Although it’s not completely impossible, the chances of a doomsday impact from outer space is actually so low that it can’t accurately be calculated in a realistic statistic, but it’s safe to say this has indeed happened at least once since life formed on Earth. Meteors happen daily and even during the day. Just because you can’t see them streak across the sky most of the time during the day doesn’t mean these same events happen less often when the sun shines down as opposed to night, because they certainly do. In fact, Earth plows through so much dust and debris on a daily basis that it’s estimated to collect between 5 and 300 metric tones of material in a 24 hour period. Most of these meteors however, never make contact with the ground and never cause damage or often hit underpopulated areas and are often never even witnessed. Although Hollywood wants you to believe that big impacts only take place over large populated areas, it’s simply not true and not even a common event to happen in anyone’s lifetime.

The next time you gaze upon the contrasting dark and glimmer of the night sky and suddenly see a streak of light across the backdrop of the night sky, know that somewhere at sometime, a comet, asteroid or meteoroid went rogue to travel a personal unfortunate journey that included a fate with a mightier object we call Earth. This is when these fast traveling rogue objects physically transform into a meteor whether it be a sporadic event or a predictable yet fantastic meteor shower. Oh and not to forget, if one of these meteors has enough material to survive its fiery descent upon Earth and actually make impact with the ground, it is then known as a meteorite.

So whether you call them meteors or falling stars, don’t forget to listen to Shooting Star by Bad Company during the next meteor shower and listen closely to the lyrics, “Don’t you know that you are a shooting star” because no matter what we call them, “all the world will love you just as long, As long as you are“.

## Guide To Comets and Meteors

According to the U.K.’s National Space Centre, there are nearly 8,000 Near Earth Objects (NEOs), or large bits of debris leftover from the formation of the solar system that pass within 45 million kilometers of the Earth: a hair’s breadth in astronomical scales. NEOs can be either asteroids or comets, and the 800 objects scientists are most concerned about are larger than a kilometer. Were they to strike the Earth, they would create havoc of cataclysmic proportions. Otherwise, much smaller rocks — meteors — come into contact with the Earth’s atmosphere on a regular basis and provide spectacular shows for both astronomers and hobbyists as they incinerate. The sections below provide a brief introduction to, and history of, some of the solar system’s smaller phenomena: comets and meteors. The information is particularly geared toward students and amateur observers, offering frequent links to external resources from NASA, the Smithsonian, professional periodicals, and individual astronomers. The penultimate section also quickly outlines some of the often confusing distinctions between meteors, meteorites, falling stars, and other objects.

The Science of Comets and Meteor Showers

In its website on the topic, the National Air and Space Museum (NASM) describes a comet as a “dusty snowball” inside an outer casing of ice that, like planets, travels in an elliptical orbit around the Sun. This solid portion, or nucleus, may be water ice or any number of substances that normally exist in gaseous states, often mixed with bits of rock. Around the nucleus is an enormous cloud of gas (up to 3 million kilometers). Finally, the tail of a comet is a trail of gasses and particles that come from the partial melting and vaporization of the nucleus from the sun’s heat. Regardless of the comet’s trajectory, the tail points away from the Sun due to solar winds. Aside from the information provided by the NASM, NASA’s Comets page provides both information and large photographs. A meteor shower, according to the American Meteor Society, is a large cluster of small particles falling into the Earth’s atmosphere at incredibly high velocities. The friction between between these tiny rocks or chunks of ice and the air in the atmosphere causes them to burn up, creating dazzling light shows. In fact, one of the main causes of meteor showers is the trail of comets. When a comet crosses paths with the Earth’s orbit, they leave behind trails of meteors called streams. When the Earth passes through one of these streams, the particles rain down on the atmosphere, providing streaks of light as they burn. The educational website, StarDate, posts a list of predicted meteor showers each year that can be seen from the continental United States.

## Astronomy Unit

Meteors
Meteors are hard pieces of rock and metal that come from outer space and burn up as they come near the Earth. They move so quickly through the air that the air burns them into a gas. This is why they are dubbed shooting stars! On a dark night, you can see about six of these an hour. This is striking because meteors are around the size of a pea. You might be wondering how we can see them if they are so small. It's really the gas around this little thing that you are seeing from Earth. Some of the time, a large number of meteors can be seen at once, which is something that is hard to predict before it happens. We think that above the whole Earth, there may be about 25 million meteors every day that are bright enough for you to see!

Asteroids
Asteroids are made up of rock and metal. They are much bigger than meteors. We used to think that they were only little planets, but soon found out that they were different. They are on the small side (smaller than the moon) and do not have enough gravity to be round shaped. They are like planets because they do follow an orbit, or a set path, around the sun. Most asteroids can be found in the asteroid belt, which is a place between Mars and Jupiter. It takes them between 3 and 6 years to travel around the sun one time. Even though there are a lot of asteroids here - we know of over one million - they are pretty spaced out. That is good for space travel because spaceships can move around without worrying about crashing into an asteroid.

## Meteors made of differing substances. Will they all burn up? - Astronomy

### Lesson 5) An Invisible Shield

Professor Gagarina enters the classroom carrying a stack of parchment in one hand and her wand in the other, levitating a large, somewhat lumpy model of the Earth on a board in front of her. The walls are covered with more posters of Earth, this time surrounded by circles in increasing sizes. After placing her items on the desk, she waves her wand towards the tower windows: a waning crescent moon and a bright, reddish star are just visible.

Earth&rsquos formation is something it has in common with all the other planets. Each formed from the same massive cloud several are formed from similar materials. Part of what makes Earth special is how it protects itself from the violent solar winds, space debris, and radiation that could tear everything apart: Earth&rsquos atmosphere and magnetosphere work together to keep all life free from most celestial dangers.

Easy as 1, 2, 3!

Earth&rsquos atmosphere has changed greatly since the formation of the planet. First, physical processes and then life itself made these changes possible. The air we breathe today is very different from the air of the early Earth. Earth is thought to have had three different atmospheres, each defined both by composition and the process that created and changed it.

Earth shares its first atmosphere with a majority of the solar system. For a brief moment after its creation, Earth was surrounded by hydrogen and helium, the most common, and lightest, elements in the universe. This atmosphere was thin and offered very little protection from the sun&rsquos rays and space debris. If you were to perform magic on this version of earth, your spell&rsquos power would be very unpredictable: the wild magic in solar wind would cause a massive backfire or the spell could be incredibly weak. Indeed, it is the shortest lived atmosphere as these elements were soon blown away and scattered by solar winds.

Source: NASA

The second atmosphere was the result of the turbulent period that preceded the formation of continents and oceans. As you learned last week, this period is known as the Hadean, where volcanos ruled and no life could be found. Gravitational forces during Earth&rsquos formation caused the planet to heat up significantly. As heat rose to the surface through the forming layers, volcanos formed to relieve the pressure under the Earth&rsquos crust. These volcanos produced carbon dioxide, sulfur, nitrogen, and water vapor which formed the second atmosphere. Magic at this time would be much stronger and have more unpredictable results than magic today. Magic released by volcanoes is &ldquowild&rdquo magic from deep inside the earth, known to have many unintended consequences. While this atmosphere is still inhospitable for most forms of life we see today, it still contains many of the building blocks for today&rsquos atmosphere.

Source: NASA

The first and second atmospheres are the result of geological processes and the direct result of the formation of planet Earth. The third atmosphere is the one we experience daily. The very first life that formed on Earth was made up of single celled plants. These plants used sunlight and the carbon dioxide from the second atmosphere to create sugar and oxygen, a process known as photosynthesis. The sugar was used as energy by the plant as it grew, while the oxygen was released into the air. Over time the amount of carbon dioxide was reduced, replaced by oxygen. Today, the third atmosphere is mostly made up of nitrogen, followed by oxygen, with a smaller amount of other gases also present, mostly carbon dioxide.

Layers Upon Layers

Just like the Earth itself, the atmosphere surrounding the planet is also made up of layers. These layers, too, are defined by mass and temperature. However, since these layers are made up of gases, substances in which molecules move freely through space, they are also defined by their density or how many molecules reside in an area of space.

Source: NASA

The troposphere is the layer of the Earth&rsquos atmosphere with which we are most familiar because this is the layer where we live. It begins at the Earth&rsquos surface, reaches a height of eleven to twelve miles, and contains three quarters of the mass of the whole atmosphere and all but one percent of all water vapor on Earth. Temperatures here tend to be higher near the surface of the Earth, getting colder as you move to the edge of the troposphere. This is because this atmospheric layer is heated by the reflection of the Sun&rsquos heat from the Earth&rsquos surface. This heating is also what produces weather on Earth. Without the troposphere there would be no breathable air or any rain to keep plants and animals alive.

The next layer is the stratosphere, it is much less dense than the troposphere but is much larger, reaching from about eleven miles up to approximately thirty miles high and contains almost all of the remaining mass of the atmosphere. This layer is of particular importance to us on Earth because it is where the ozone layer and other particles absorb a majority of the Sun&rsquos ultraviolet radiation and filters raw magic coming from the Sun. Without this layer magic and radiation from the Sun would greatly harm all life on Earth. The Sun&rsquos magic can be considered &ldquowild&rdquo and raw, but when filtered through the stratosphere, it is rendered more stable, predictable, and uniform. This absorption of energy creates a lot of heat, and despite the low temperatures where the troposphere meets the stratosphere, as you move farther from Earth the temperatures rise dramatically.

The mesosphere is the layer located on top of the stratosphere. It begins about thirty miles away from Earth&rsquos surface and extends to about sixty miles away from the planet. Here, temperatures drop again as you move further away as there are fewer molecules that absorb solar radiation and the outer edge of the mesosphere is the coldest place on Earth. There are still enough particles in this layer to interact with outside objects: most meteors bound for Earth burn up in this layer as they encounter massive amounts of friction with Earth&rsquos atmosphere. Without this layer a greater number of meteors would be able to hit the Earth, causing death and destruction.

The next layer is the thermosphere which begins about sixty miles from Earth&rsquos surface and reaches up to three hundred miles away. While this layer is actually very hot, this heat cannot be felt. Feeling heat requires hot, energetic molecules to transfer their energy to your skin since there are so few molecules in this layer, the energy cannot be transferred and heat cannot be felt. Earth&rsquos gravity is not only strong enough here to hold gas molecules, it can hold larger objects as well. This layer is most notable as the home of the International Space Station, where astronauts from around the world live and study in space.

The largest, least dense, and outermost layer is the exosphere it begins three hundred miles from Earth and ends about sixty-two hundred miles away. Here you can find stray molecules of hydrogen and helium, though at the outer edge these are indistinguishable from particles in the solar winds. Earth&rsquos gravity still affects this layer enough to keep objects in place in orbit: here is where you will find most of the satellites orbiting the planet. They are an advanced form of Muggle technology, allowing them to transmit information and images around the world very quickly. Wizards are also looking to begin developing satellites of their own, but these projects are generally still in the research phase.

Source

One Massive Magnet

While Earth&rsquos atmosphere is a powerful physical shield that can stop both solid objects and radiation from hurting us, the planet also has its own invisible armor. As mentioned before, the solar wind is a stream of particles from the Sun that is strong enough to blow away atmospheres. Earth&rsquos magnetic field, however, can deflect these particles away from us and maintain our atmosphere.

Source

Earth&rsquos magnetic field is generated by the Earth itself. It helps to think of the planet as a magnet. Magnetic force is generated in the outer core. Here molten iron rises from the inner core, cools slightly, and moves back towards the inner core again. The interaction of this much iron in motion creates a planet-sized magnet. We can see this when we use a compass: the needle is magnetized so that it will always point towards the magnetic North Pole.

The massive magnetic field creates the magnetosphere. Here, charged particles are held in place by the magnetic field of the Earth. These particles help to interact with and deflect the solar wind around our planet. This interaction can be observed by the naked eye. Auroras like the Aurora Borealis are created when solar wind and the magnetosphere collide. These collisions make the lights that we see rippling very high up in Earth&rsquos atmosphere, usually the thermosphere.

Source: arctickingdom.com

That will be all for this week. To date you have studied the formation of the Earth and its features, as well as how the Earth is able to protect the organisms that live upon it. At the end of this lesson there will be a short quiz to test your knowledge on the newest information and also a midterm test, focusing on all that we have studied so far this year. When you have completed all your assignments, stop by my desk for a slice of Earth layer cake!

Our Big Blue Marble - Earth is the only planet we call home it is what gives us life and security even as we look to the heavens all around us. In order to study the heavens, however, it is first necessary to understand ourselves. What makes the Earth so special and why are we the only planet in our whole Solar System known to contain life? This year is intended to give Astronomy students a foundation in our Earth even as we seek to compare ourselves to others. Students will leave this class with a better understanding of their own place in the universe, the ability to compare Earth with other planets, knowledge of the origins of magic in our near universe, and an appreciation for the uniqueness of the planet we call home.

## Amazing photo of the Quadrantid meteor shower… from space!

The recent Quadrantid meteor shower in early January was something of a bust for most people while it did produce shooting stars, it was not quite up to the rate predicted (absolute max of 100/hour, though for most people about half that). I hope to eventually see a paper saying why that might be.

But some folks got a good view of the shower. Amazingly, it wasn’t from someone who looked up to see the meteors burning up in our atmosphere. It was from someone who had to look down.

International Space Station astronaut Christina Koch tweeted this shot a couple of days after the Quadrantid peak:

WHOA. Look to the left: You can see several trails from bits of asteroid 2003 EH as they hypersonically plow through our upper atmosphere, about 100 km off the ground. At the time, the space station was 320 km higher yet.

When I first saw the photo I was alarmed, but Koch's caption eased my mind: She notes explicitly that this is a composite of several photos. Ah, that makes sense! A photo like this has a short exposure time, and the odds of catching a meteor at all are low, let alone 3, which is why my skeptical alarm bells were ringing.

I’m not sure how the photo was composited, though. Curious, I went to the Gateway to Astronaut Photography of Earth, a fabulous website that has a vast number of astronaut photos online. Better yet, they’re searchable! Knowing the peak of the shower was on 4 January, I limited my search to that date (click here, then click the "Uncataloged Image Search" button, then enter 4 January 2020 for both the start and end dates) and was able to quickly find the series of photos used for the composite.

If you do this, you can see the city — which I suspect is Edmonton, Alberta, given the ISS was southwest of it at the time — featured so prominently in the photo in many of the shots, moving to the lower left as the ISS moved around the Earth (the photos are displayed in reverse chronological order). There are several dozen shots, but it wasn’t hard to find a couple with meteor streaks in them:

A Quadrantid meteor seen from the ISS, taken on 4 January 2020 at 11:29:46 GMT. Credit: NASA

A Quadrantid meteor seen from the ISS, taken on 4 January 2020 at 11:30:17 GMT. Credit: NASA

The second shot was taken 31 seconds after the first you can see the city lights have moved. The cloud cover has changed a bit, too, most likely due to the changing perspective of the station as it swept over the region at 8 kilometers per second. I tried to move the two images to make them overlay and it doesn’t work well due to the perspective change when I shifted them so the city is in the same place the other bright spots didn’t match up correctly.

I suspect then that whoever made the composite cut out the meteor trails and pasted them into a different image — I'm sure I could find that master image if I poked through the archive a bit more. Feel free if you want to.

So that’s pretty cool! The photo is real, if composited (which I'm fine with — some hoaxers or content stealing accounts like to grab something like this and pass it off as a single shot, which is grossly misleading at best), and it shows something completely amazing: What a meteor shower looks like from space.

You may be wondering how dangerous it is to be in the space station during a meteor shower. The answer is: Not much. There's a risk, certainly, but it’s small.

A Perseid meteor taken by astronaut Ron Garan on board the International Space Station in 2001. Credit: NASA

Back in 2011, my friend and astronaut Ron Garan took an iconic photo of a Perseid meteor from the ISS. I wrote about it at the time (this was back when I was with Discover Magazine) and did a little bit of math to figure out just how risky it is. The number I got is that, on average, the ISS would get hit by a Perseid once every 8,000 years. Even adding up all showers, it's unlikely the station would get hit during any given astronaut’s stay. Over enough time, yeah, it will inevitably get hit by one, but we’re talking a timescale of centuries. So it's not a huge day-to-day concern.

I'll note they do have emergency patches on the ISS in case of a hole. Given that a typical meteor shower meteoroid is smaller than a grain of sand and moving at roughly 40–80 kilometers per second, it will leave a teeny tiny hole, punching right through the station wall as if it weren’t there. As long as it doesn't hit something vital, like a computer, an air tank, or, say, an astronaut, they'll have plenty of time to find the hole and fix it. The air would leak out very slowly.

Crash Course Astronomy: Meteors, Meteoroids, and Meteorites, Oh My!

The bottom line is the space station is small relative to the Earth, space is bigger yet, and the odds of it getting hit are low… but we keep putting more and more hardware into space. At least one if not two satellites have been hit in the past, causing them to lose control and forcing them to be shut down. The more we launch into the space, the more often this will happen, and it's something engineers need to be aware of.

One more thing: From the ground, we see meteors appear to come from a point in the sky called the radiant it's a perspective effect. From space, the meteor trails should look parallel. But they don’t in the photo! I think again this is due to the motion of the station orbiting the Earth, but I'm not sure. The geometry here is a little tricky. If you have ideas, feel free to leave a comment below! I’m curious to know if anyone out there who has experience interpreting ISS photos of Earth has anything to say about that.

## Explainer: Understanding meteors and meteor showers

Here’s a shooting star, or tiny meteor, moving through Earth’s atmosphere. The streak of light this space rock left behind has shades of green and purple.

RobertHoetink/iStock/Getty Images Plus

December 13, 2019 at 6:30 am

Every once in a while, on a clear, dark night, a tiny streak of light flashes across the sky. Commonly called a shooting star, it’s actually a space rock — usually a quite small one. It creates light as its friction with Earth’s atmosphere causes its outer surface to catch fire and burn. At certain times of year, a reliable “shower” of these rocks can enter the upper atmosphere, creating a fleeting light show.

Bigger incoming rocks can pass all the way through the atmosphere, creating a sonic boom and trail of falling rocky debris.

#### Death by asteroid may come in unexpected ways

So how big are these rocks and where do they come from? The simple answer is, it varies — widely. They tend to be what’s left in the wake of comets or space junk. Some may even be asteroids. That last type can be plenty big enough to pose a lethal risk to anything in their path.

Most, however, are silent, high-flying shooting stars. They enter the air as pebbles about the size of a pea. That means you could stow an entire locally viewed meteor shower in your backpack.

The source of a meteor shower will depend on which one you’re watching. Each tends to take place at about the same time each year — when Earth plows through some long-lasting field of debris. This happens at the same point in our planet’s annual orbit around the sun.

It’s kind of like driving on a warm summer day when your car enters a swarm of bugs. Even if the bugs are hovering and relatively still, their collision with your windshield will yield a loud splat (and leave a nasty streak on the glass). When a large enough meteor explodes in the lower atmosphere, it can cause a loud boom, depending on its size. It also sends a streak of light into the sky.

Earth’s atmosphere is made of layers of air that become successively thicker the closer they get to the ground. When incoming space rocks hit the mesosphere, they encounter enough friction from that air that they heat up and start to burn. Crystal-K /iStock/Getty Images Plus

Earth’s gravity tugs at any nearby space rocks. As they get pulled into the upper atmosphere, they encounter drag. This friction releases an enormous amount of heat, igniting the meteor. The resulting fiery blaze can display a range of colors.

Every meteor shower has a radiant. That’s a point in the sky from which all the meteors appear to come. It’s the direction Earth bulldozes through the debris stream. So the planet strikes individual rocks head-on from that angle. If you look right at the radiant, you’ll see only a quick flash of light. But meteors that you catch while looking at a right angle (sideways) to the radiant will have long, vibrant tails.

Think about it like driving through a snowstorm at night. Imagine looking forward through the windshield. All the snowflakes seem to be heading straight at you because you’re moving straight at them. But gaze out the left or right window and the falling flakes will look like soft, white specks of light buzzing by. That’s because you’re moving parallel to the flakes’ motion.

#### Where do their colors come from?

Every meteor streak has its own unique character. So do the showers.

December’s Geminids are the most spectacular of all. They blaze emerald green, pink and violet. The August Perseid shower sends streaks of pink, lime green and purple. They flash across the sky in the blink of an eye. The Orionids in October are faster still but dimmer. Their streaks have a soft whitish-orange shimmer.

Two processes account for those hues.

As a meteor hurtles through the vacuum of space, there’s nothing to slow the extraterrestrial rock down. But once it encounters air resistance at the edge of Earth’s mesosphere, some 80.5 kilometers (50 miles) up, the rock gets hot. Enormously hot! That heat eventually causes the rock to burn. Its flames will have different colors, depending on the rock’s composition. Its elemental recipe determines the color of its glow. Metallic elements tend to burn brightest.

Researchers with the Astronomical Institute of the Academy of Sciences of the Czech Republic studied this in 2008. They looked at Geminid showers between 2004 and 2006. The “meteors were observed by image-intensified video cameras,” they reported. Then they applied a process called spectroscopy (Spek-TROS-koh-pee), which looks at how materials interact with light or emit light. This showed that some of the burning rock had been rich in magnesium, sodium and iron. The Perseids in August showed evidence of silicon and calcium, too.

If all these elements sound familiar, that’s because you’ve likely seen them on the back label of your breakfast cereal. Froot Loops contain them all. But that doesn’t mean dumping a bowl of Lucky Charms out your second-floor window will trigger a meteor shower. Indeed, speed is as important as the rocks’ ingredients.

As a meteor speeds through the atmosphere, it compresses the cushion of air trapped ahead of it. That “air pillow” is squeezed so much that it heats. When molecules absorb enough energy (here, heat), they can become excited — in a physical sense (not an emotional one). Afterward, they’ll release packets of light known as photons. The more energy going in, the more energetic the light that is later released. Higher energy photons will emit light having a higher frequency — also known as a higher wavelength. Purple light has a higher frequency than red. Ultraviolet light has a higher frequency than infrared.

Most meteors entering Earth’s atmosphere burn up before reaching the ground. But there are the exceptions. This Barringer crater in Arizona marks where a 30- to 50-meter (98- to 164-foot) meteor survived to crash into the Earth 49,000 years ago. StephanHoerold /E+/Getty Images

Because the Geminids are slower, their light is mainly green. But even after a meteor has passed, it takes a while for the air molecules’ energy level to fall back to normal. That’s why a shimmering tail of light remains. That light also may be accompanied by smoke.

It’s very rare for a meteor to survive and crash into the ground. On average, one basketball-sized meteor falls to Earth’s surface each month.

To reach the ground, it must start out big enough so that it doesn’t burn completely during its trek through the atmosphere. One space-boulder crashed down just west of Detroit, Mich., in January 2018. Nearly 50,000 years ago, a far bigger one excavated 175 million tons of rock in what is now Arizona. The Barringer crater it left behind is nearly 1.6 kilometers (1 mile) wide and 174 meters (570 feet) deep.

Meteors that survive to reach the lower atmosphere hit more air resistance and as a result burn very bright. These are termed fireballs. The December Geminid showers and August’s Perseids produce large numbers of fireballs.

#### How predictable are shower forecasts?

Weather permitting, people can see meteor showers many times a year. The Geminids’ peak shower spans several nights around the second week of December. Its light streaks tend to be bright, offering some of the best viewing of the year.

The Quadrantids arrive every January. They boast large numbers of shooting stars. In some years, people at many locations can see up to 100 per hour. But such peaks last only a few hours.

Debris left by Halley’s Comet is the source of two showers. The first, in May, is known as the Eta Aquarid shower. The October Orionids is the second. (Halley’s Comet last swept through the night sky in 1986. It won’t be back until 2061.)

The Areitid shower peaks around June 7th. It can bring more than 50 shooting stars per hour. That makes for comfortable warm viewing in the Northern Hemisphere. One might think that would make these showers widely viewed. In fact, they aren’t. Their radiant is so close to the sun that they are best seen right before sunset or sunrise. And because they are competing against that sunlight, only the brightest of the meteors will be visible. Plus, they mostly shower during the day. So unless a total solar eclipse blocks out the sun, they’ll zip through the skies unseen.

The August Perseid shower tends to be the most popular. It can send some 75 to 100 colorful meteors per hour across the sky. And the viewing will be summer warm in the Northern Hemisphere.

A handful of other lackluster meteor showers dot the night skies in other months, such as the Leonids each November. During its peak, that shower usually issues only about 15 meteors per hour. But even the Leonids can sometimes offer surprises.

In 1966, this usual dud of a shower started our pretty quiet. Cloud cover socked in the East Coast. Out West, only the occasional few blips of light confirmed the Leonids had arrived. As a result, most stargazers went to bed disappointed. Back then, 10-year-old Joe Rao was among them. Now a meteorologist, he has never forgotten hearing what he missed that night.

After 5 a.m., the sky seemed to explode. A torrential downpour of meteors sent more than 150,000 streaks of light across the sky in a single hour. That comes to more than 50 per second. After 90 incredible minutes, it was over. Such “meteor storms” develop when Earth’s orbit cuts through a trail of dense debris left by a comet or asteroid.

What causes it? A large fragment likely broke off some huge rock, perhaps shattering in the process. That left a narrow and extremely dense cluster of shards. Once every 33 years or so, Earth passes through one of these pockets to create a Leonid storm.

#### What if it’s cloudy?

Clouds can easily spoil the show from Earth’s surface. But that doesn’t mean the fun is ruined. NASA has a radar “listening station” for meteors in Huntsville, Ala. It lets anyone tune in to hear the blips as the shooting stars zip through the atmosphere. The radar signals are converted to sound waves. It’s best to listen for these during what would be Alabama’s predawn hours. That’s when more meteors enter the atmosphere — and do it with a greater velocity. This makes them easier to resolve on NASA instruments. And subsequently, you have greater odds of hearing the agency’s so-called “meteor radar.”

NASA is currently working on this system (so it is now unavailable). Meanwhile, another antenna in Washington, D.C., offers an alternative portal as a way to listen in.

### Power Words

angle The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

annual Adjective for something that happens every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.

antenna (plural: antennae) In physics: Devices for picking up (receiving) electromagnetic energy.

asteroid A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

atmosphere The envelope of gases surrounding Earth or another planet.

average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

bug The slang term for an insect. Sometimes it’s even used to refer to a germ. (in computing) Slang term for a glitch in computer code, the instructions that direct the operations of a computer.

calcium A chemical element which is common in minerals of the Earth’s crust and in sea salt. It is also found in bone mineral and teeth, and can play a role in the movement of certain substances into and out of cells.

comet A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”

crater A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.

debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

develop To emerge or come into being, either naturally or through human intervention, such as by manufacturing.

drag A slowing force exerted by air or other fluid surrounding a moving object.

eclipse This occurs when two celestial bodies line up in space so that one totally or partially obscures the other. In a solar eclipse, the sun, moon and Earth line up in that order. The moon casts its shadow on the Earth. From Earth, it looks like the moon is blocking out the sun. In a lunar eclipse, the three bodies line up in a different order — sun, Earth, moon — and the Earth casts its shadow on the moon, turning the moon a deep red.

element A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

extraterrestrial Anything of or from regions beyond Earth.

fireball A lump of rock or metal from space that hits the atmosphere of Earth. Fireballs are meteors that are exceptionally bright and large.

frequency The number of times some periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

friction The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.

gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

hue A color or shade of some color.

infrared A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.

iron A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

literally A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

magnesium A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in Earth’s crust.

mesosphere The highest part of Earth’s atmosphere where all of the gases are all still well-mixed, not merely layered on the basis of each gas’s mass. This layer, found immediately above the stratosphere, is 35 kilometers (22 miles) thick. It’s the uppermost layer of the atmosphere with enough gas to cause friction for incoming space rocks. That’s why this region is where most meteor’s burn up. It varies somewhat in height, but tends to span about 50 to 80 kilometers (30 to 50 miles) above Earth’s surface.

meteor (adj. meteoritic) A lump of rock or metal from space that hits the atmosphere of Earth. In space it is known as a meteoroid. When you see it in the sky it is a meteor. And when it hits the ground it is called a meteorite.

meteorologist Someone who studies weather and climate events.

molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O 2 ) water is made of two hydrogen atoms and one oxygen atom (H 2 O).

NASA Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

parallel An adjective that describes two things that are side by side and have the same distance between their parts. In the word “all,” the final two letters are parallel lines. Or two things, events or processes that have much in common if compared side by side.

photon A particle representing the smallest possible amount of light or other type of electromagnetic radiation.

physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

radar A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land — even land covered by ice.

radiant (n.) The point or object from which light or heat radiates (such as the heating element in an electric heater). Or the point from which objects (such as meteors) appear to come.

range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

resistance (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

right angle A 90-degree angle, equivalent to any inside corner on a square.

risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

shard A piece of broken pottery, tile or rock, or a hard, broken piece of anything that has an irregular shape.

silicon A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

sodium A soft, silvery metallic element that will interact explosively when added to water. It is also a basic building block of table salt (a molecule of which consists of one atom of sodium and one atom of chlorine: NaCl). It is also found in sea salt.

solar eclipse An event in which the moon passes between the Earth and sun and obscures the sun, at least partially. In a total solar eclipse, the moon appears to cover the entire sun, revealing on the outer layer, the corona. If you were to view an eclipse from space, you would see the moon’s shadow traveling in a line across the surface of the Earth.

sonic Of or relating to sound.

sound wave A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

swarm A large number of animals that have amassed and now move together. People sometimes use the term to refer to huge numbers of honeybees leaving a hive or a large number of grouped particles that are moving.

tune (in engineering) Adjust to the right level.

ultraviolet light A type of electromagnetic radiation with a wavelength from 10 nanometers to 380 nanometers. The wavelengths are shorter than that of visible light but longer than X-rays.

unique Something that is unlike anything else the only one of its kind.

vacuum Space with little or no matter in it. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.

velocity The speed of something in a given direction.

wake An area of disturbed air or water left behind an object (such as a boat or animal) moving through it.

wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

### Citations

Explainer: Spaceweather.com. The MFSC Online Meteor Radar In cooperation with Rob Suggs, Bill Cooke, and Jeff Anderson of Marshall Space Flight Center in Huntsville, Alabama.

Article: NASA Jet Propulsion Laboratory. How to see the best meteor showers of the year. Aug. 9, 2016.

Meeting: J. Borovička et al. Structure and composition of Geminid meteors and implications for the nature of Phaethon. Astronomical Institute of the Academy of Sciences. Presented at the 10th annual Asteroids, Comets, and Meteors meeting. July 14-18, 2008.

Journal: J. Licandro et al. (2006). The nature of comet-asteroid transition object (3200) Phaethon. Astronomy & Astrophysics. Vol. 461, January 11, 2007, p. 751. doi: 10.1051/0004-6361:20065833.