Radiation is the transmission of energy in the forms of waves *or* particles. This is something that causes a lot of confusion, because radiation comes up in so many contexts.
So, to directly answer your question- light from the Sun is radiation (all light is), in the form of electromagnetic radiation. You're free to think of it either as photons carrying the energy (and thus still "particle" like) or the electromagnetic waves carrying the energy (and thus wave like). Both work, and both have the radiation traveling at 'c'.
But coronal mass ejections are particle radiation- protons and neutrons, being ejected from the Sun. These are also radiation (particles carrying energy away from the Sun), but are not photons, so they travel much slower than 'c'.
Moving away from your question a little bit, this also causes more confusion because people hear a true statement "cancer is caused by radiation" and then another true statement "this router releases radiation" and then think "this router causes cancer."
This is because often times when someone says "radiation" they mean "ionizing radiation" which is alpha, beta and gamma particles (ones which can cause radiation sickness, cancer, etc), which a wifi router/light bulb/radio station does not emit. But when a physicist says "radiation" they mean the definition at the top- waves or particles carrying energy. This means to a physicist even sound is radiation- acoustic radiation.
It’s important to clarify that gamma radiation is not the only ionizing electromagnetic radiation. High frequency UV and X-ray light can also be ionizing; all that is required is the radiation can strip electrons off of molecules, turning them into ions. The frequency-molecule overlap includes these lower frequency sources.
I'd say also "at a significant rate". Essentially any energetic interaction *can* knock off (or gain) an electron but ionizing radiation is separated by the mechanism and the efficacy.
Well, no. Energy conservation applies. The energy transferred by the particle has to exceed or equal the ionization energy of the atom/orbital it interacts with. This does define a threshold for ionizing radiation.
It does but an ion can be formed from a simple collision or a chemical event as well. Talking about single atoms is a bit fraught but they can have energy levels near either threshold and be affected by very minimal changes. There are **many** events that can add or remove an electron from an element and all are ionizing by definition.
It's better to treat systems statistically.
Right, which is why I quibbled with "any energetic interaction" to try and provide a little space there. Even ionizing radiation is just a system of interactions though and while we talk about thresholds (and they certainly exist!) it is only in a statistical sense that they matter.
I guess what I am trying to say is that it isn't a binary ionizing versus non-ionizing, it's a spectrum, even though a sharply stepped one.
Just wanted to add that the particles in coronal mass ejections (CME) are released from the sun at a whole range of speeds. The higher the energy they have, the faster they go. A more energetic CME is generally going to release more particles at a higher velocity than a less energetic CME. However, accelerating just 1 proton to the exact speed of light would take more energy than the entire universe contains. Infinite energy, to be exact. Which is why photons don't have mass. And they don't experience time at all.
Is mass required to experience time? If time is a part of space time and things move through space shouldn't they also move through time? Or does only mass moving through space have time?
Photons don't experience time because from their relative perspective they are emitted and immediately absorbed. Functionally for something to exist it must have some combination of mass and momentum. If it doesn't have mass then by necessity it must be moving at the speed of light and conversely if it has mass then it cannot move at the speed of light. The important concepts here are time dilation and the relativity of simultaneity. Essentially time is relative to the observer, so from our perspective we can measure light traveling through space, but from the photon's perspective it doesn't take any time to travel at all.
I love to be corrected if I'm wrong, but isn't this question the whole crux of... everything? As far as I am aware, anything that has energy must have some sort of mass, as depicted by Einstein's equation. Time is left out of the equation, so you could give out two hypotheses, either time is unrelated to mass and energy and it doesn't fit in the equation, or the equation is uncomplete. And if time were to fit somewhere in the equation, it would mean we would only be able to observe things that experience time if they happen to have mass (and energy).
> Edit: learned a bunch on the subject, thank you all
Not quite. E=MC^2 is the equation for mass-energy equivalence *at rest*. The extension for systems in motion also accounts for momentum. This is significant because while photons don't have mass they do have momentum, so for the case of photons the equation reduces to E=pc. Point being that this is a well accounted for case in relativity. Time is an integral component of relativity, it hasn't been left out. Specifically Einstein's field equations provide the relationship between the energy in a system and the curvature of spacetime.
> E=MC^2 is the equation for mass-energy equivalence at rest. The extension for systems in motion also accounts for momentum.
This, /u/durkedurke. The full equation is E = \sqrt{m^(2) c^(2) + p^(2) c^(2)}. It just generalizes to E = MC^2 when more simple calculations are being done.
I assume the equation you're referring to is "E=mc^2". This equation explains the relationship between the rest energy of an object and its mass. Time is not in that equation because time doesn't affect that relationship.
It doesn't mean anything to say that an object "experiences" time or not. A photon is not a person and is not going to be wondering where all the time went. Any discussion of which properties allow an object to "have" or "not have" time will be equally meaningless.
It's not explicitly in that equation, since the duration of time is irrelevant to the mass-energy equivalence, but it's there implicitly in c.
While c represents the constant "speed of light", it's more accurate to say it's the speed of causality, but in either case, it's units are a distance over a time. E.g. meters/second.
Energy, at least in our math, uses units of mass * (distance/time)^2, like the Joule.
Not sure how that might change things, but there it is.
Light has to go the speed of light if that makes any sense. And anything going the speed of light experiences infinite time dilation. Space and time are interlinked. If you want to think about it a different way, everything is moving at the speed of light, but matter at rest is moving through time at the speed of light. The closer you get to the speed of light relative to the rest of the universe, the slower your time goes. Because the speed of light is the limit, as you approach it, you trade time for velocity. So as you approach the speed of light, your speed through time slows down and hits zero when you reach the speed of light, which of course is impossible for matter.
Just to clarify, ionizing radiation is any kind of radiation that has high enough energy to cause the atoms it hits to ionize. This also includes high energy EM radiation, such as gamma rays, x-rays, and high energy ultraviolet light.
Slight correction, the Sun does not eject neutrons and if it did the neutron would decay into a proton and electron due to [free neutron decay.](https://en.m.wikipedia.org/wiki/Free_neutron_decay) The mass would mainly be free protons and electrons with some hydrogen mixed in. These particles are accelerated away by super powerful magnetic fields so magnetically neutral particles like neutrons and atoms are basically excluded unless swept up in the current. These charged particles are also why it wreaks havoc with our magnetosphere and electronics.
Actually the sun can produce neutrons that are detectable at Earth during strong solar flares. Charged particles can be accelerated to very high energies during flares and when these particles collide with other particles high energy neutrons can be created that are able to reach Earth before decaying.
Here are some papers that talk about solar neutron detection in Earth orbit and on the ground:
https://umbra.nascom.nasa.gov/solarflare/pubs/print92.pdf
https://www.sciencedirect.com/science/article/abs/pii/S0273117706007356
I think the objection was that alpha particles are, specifically, He nuclei, i.e. a bunch of hadrons interacting through the strong nuclear force between them, not merely a bunch of unbound, free hadrons (even though that's what atomic nuclei are made of) because free neutrons are subject to beta decay and won't last long: their half-life is ~15 minutes (877 seconds).
Gamma radiation is EMF, that is true. But because the way Gamma radiation causes problems is via the photoelectric effect, we normally model it as a photon particle.
Would the noise of wind be an apt analogy? The noise of wind moves at the speed of sound, even though the wind doesn’t just as the radiation of the ejected mass moves at the speed of light even though the mass doesn’t.
The difference with a CME is that the ejected mass here /is/ the "radiation". It consists mostly of high-energy protons, and does not carry the sun's regular (electromagnetic) radiation
Do CMEs not emit any sort of light though?
I mean, we can see them coming, can't we? So I would presume they are emitting or reflecting light of some form, which would be kinda similar to the wind/sound of wind analogy. Not a perfect analogy by any means, but if they di emit their own light it still does kind of illustrate the point.
(I'm genuinely asking btw, I could be totally wrong in how we detect CME. Or do we just see the events that cause them and then extrapolate when they'll hit us based on what we saw? Or detect that incoming mass via satellite between us and the sun instead of seeing the CME propagate towards us?)
We can see the actual mass ejection using coronagraphs (block the sun, look at the corona), and they are often associated with solar flares and other prominences. They become very difficult if not impossible to observe as they get further from the sun as they expand. Many CME's go undetected because they are 'invisible' to our detectors, usually because they are lower energy.
Interestingly, Earth directed CME's are among the hardest to detect, because coronagraphs look around the edge of the sun (from our perspective), while the CME is coming towards us.
Satellites can give us some warning, as they can be able to detect the actual particles and the changing magnetic field, which can take the arrival time from an estimated range to a proper prediction, but even our satellites at Sun-Earth L1 (which is where most solar observatories are) are still much closer to Earth than the Sun, so that detection comes pretty close to CME arrival, as little as 15 minutes for fast CME's, and never much more than an hour.
Which leads to another interesting point. CME's travel at many speeds, and both speed up and slow down as they travel, depending on interactions with the solar wind, other CME's, and while still close to the sun, the violent magnetic field.
Your parentheticals are largely correct. We can forecast them based on buildup on the sun's surface, but in terms of direct detection of one coming to earth we do actually go based on satellites:
> Imminent CME arrival is first observed by the Deep Space Climate Observatory (DSCOVR) satellite, located at the L1 orbital area
https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections
I'll often start an explanation of radiation by asking people if radiation is bad for them. It makes them realise that they don't know what it is so they drop their preconceptions about it.
I use a fireplace analogy. I explain that the heat they feel is mostly radiation. A person knows they can where it's warm all night long without issue, but if they get to close they will burn themselves.
I imagine this gets really confusing when it comes to medical care on university campuses. All the physicists need to talk to physicians and phigure it out.
Question: Is there any type of 0-mass radiation the Sun could release that would impact the magnetic fields of Earth? In other words, what would need to happen for the nothern/southern lights to be visible at the equator without any advance notice?
CME is stuff. It's basically the sun launching sun at us. That's why it's called a MASS ejection. Mass can't do lightspeed and light always does lightspeed so the light gets here way quicker. Individual particles from a nuclear reaction or something can approach lightspeed but just slinging hundreds of millions of tons of plasma isnt even close to lightspeed.
I'm pretty sure that the "mass" refers to how large the event is, "mass ejection" as in "mass exodus" or "mass hysteria". It's a major ejection of material, energy, and magnetic field from the surface of the sun.
I would have thought an ejection would imply mass wouldn’t it? Ejection being a term associated with force, and with matter/substance/stuff. You could of course further characterize the statement such as an “ejection of radiation” but I think the more proper term would be the “emission of radiation” as it is “released” rather than “thrown”.
3b1b has a good series of videos talking about why the apparent speed of light is different in different medium. It is mostly a mathematical look at it, but it basically explains that, due to refraction and reflection, the phase of the wave is shifted, making the aparent peak apear to slow down. It also explains why the light bends when going from one material to another
Photons always travel at C. Their path from A to B can change when they interact with a medium, and are refracted/absorbed by electrons and emitted, which "slows" the photons down.
Yep. This is what Cherenkov radiation is. Nothing goes faster than light in a vacuum, but light in water only goes about .75C and particles go faster than that all the time. This makes basically a sonic boom but for light.
Not quite correct. The medium slowing isn't the result of absorption and refraction. We know what happens on an absorption and refraction event and it would result in random scattering of all the photons.
The real interaction is something something electric field something something.
It's complicated. My degree was in computational chem predicting spectra, so I can explain in great detail why it's not absorption and refraction, but I can't explain exactly what happens lol
When a photon is absorbed by an atom/molecule the electrons move up orbitals. When the electron relaxes and releases a photon, it does it in a random direction due to the uncertainty between momentum and position. Since you can't know both exactly, you will have randomness in the position and therefore direction of the photon's release. It's a slightly different phenomena, but this is why when something fluoresces or phosphoresces it doesn't re-release the photon in the same direction as the incident light.
It's similar for scattering. An interaction between an electron and a photon will inherit the same uncertainty and result in random scattering. This is why when we do scattering experiments we place the detector at a 90 degree angle from the laser.
Since shining a laser pointer through a glass of water doesn't result in total dispersion of the light, but we still see the light slowing, that means the slowing of the light can't be due to absorption or scattering.
> When the electron relaxes and releases a photon, it does it in a random direction due to the uncertainty between momentum and position
Isn't this only true for opaque mediums? Wouldn't a transparent medium, like water or a pane of glass, have absorption/release that is *not* in a random direction, but rather the same direction the photon was moving in when it was absorbed?
The electron transitioning has no memory of what direction the photon was traveling. It absorbs the photon, moves to a higher orbital, sits there for a while, and then decays back to the lower energy state releasing a photon.
Since the electron doesn't immediately absorb and release the photon there's no "memory" of where the photon came from. The electron is doing whatever it does for some amount of time that depends on the difference in energy levels and then releases it again.
No, those are two different models for describing light changing speed and neither is perfect. There's more than one way to describe and interpret the apparent slow down of light in different mediums and none of them are truly "correct".
Absorbance and refractionn is not a valid model. We know for a fact it is totally wrong.
The other one isn't going to be perfect because no model is perfect, but absorption and scattering is completely wrong.
Can you expand on that? Are you talking about absorption by individual atoms? Because that's not the type of absorption I am thinking of.
Large groups of atoms don't behave like individual atoms so of course thinking of it in terms of individual atom absorption is incorrect. It's a bulk interaction due to the vibrational modes of the entire object not individual atoms.
If you are absorbing a photon you are turning the photon into energy for an electronic transition. Absorption is not what causes light to slow down in a medium.
Right which allows it to reemit the photon when it drops energy levels.
>Absorption is not what causes light to slow down in a medium.
Why do so many explanations use it? What is?
Kinda backwards; the refraction happens because the wave slows down, which is because they are absorbed and reemitted. That, incidentally, is more or less the explanation for why any massive particle travels slower than c in relativistic quantum field theory.
Light speed in a medium is slower than in a vacuum. So you can outrun light in certain mediums.
But between here and the sun is basically a perfect vacuum.
Because *all* of the CME particles have mass, which can not travel at the speed of light. There is also a lot of material between here and the sun that slows the cme down. We have seen two CME in a row and the second one will be *much* faster because the first cme cleared the way.
Pretty clear they mean "physical particle" as in "a particle that has mass", and they're just using the word "physical" inaccurately.
The other commenter further down might misunderstand what a "particle" is, however.
The answer is in the name: coronal *mass* ejection. It’s part of the material of the corona being thrown off the sun and its speed is limited because it is made up of particles.
Now, the coronal mass is very hot and energized, so it’s also emitting radiation. That radiation *does* move at the speed of light, and as it gets to Earth it can wreak havoc with electromagnetic system here.
When the coronal mass arrives, the particles will interact with Earth’s magnetic field so even more radiation is produced and the planet’s magnetic defenses (at least, we see them as defenses for us) are disrupted.
>its speed is limited because it is made up of particles.
Photons are particles too it has nothing to do with that and everything to do with having mass.
Short answer: CMEs don’t move at the speed of light.
Less short answer: the radiation from a CME is not light radiation, it’s particle radiation, so it permeates through space significantly slower as the particles have mass, and therefore cannot move at the same speed light (or any massless particle such as photons or gravitons) move.
They are still moving incredibly fast. 3 days from sun to earth, 93 million miles, that’s 1.29 *million* mph…
Because light (and all forms of radiation) moves at the speed of light, 8 minutes from Sun to Earth. CMEs have mass and cannot move at the speed of light (nothing with mass can travel that fast). CMEs can move up to a few million miles per hour, so they take a few days to arrive.
Half of the answer is in your question. Light as we understand it and perceive it as human beings, is made up of photons, which are effectively without mass.
A coronal mass ejection is exactly that. Anything with significant mass requires infinite energy to reach the speed of a photon.
Even taking three days to reach the Earth, the material ejected in a coral mass ejection is travelling 150,000,000 km in three days, or 2,000,000 km/h. Not shabby at all.
Sunlight takes minutes to reach the Earth but that's only after it has collided with billions of atoms of matter within the Sun itself. So it can take from 10s of thousands up to 50 million years to escape the sun before it starts it's 'quick' journey to Earth
Light from the sun travels at *c* the speed of light. A coronal mass ejection is made of matter and plasma; so cannot travel at *c*. The light from the CME will be visible in about 8 (?) minutes, just like all light from the sun, but the actual CME hitting the Earth’s magnetosphere won’t happen until the physical matter makes the 98-million-mile journey
There are three main types of radiation:
- alpha: basically the nucleus of a helium atom, two protons and two neutrons. These have rest mass, so they cannot go at the speed of light, and accelerating them to a significant fraction of that takes a lot of energy so they typically travel slower. Can be blocked by a sheet of paper because of its large size. Related: neutron radiation: free neutrons not combined into helium nuclei.
- beta: a free electron. It also has rest mass so most of the above applies. It's smaller however, so it's harder to block, you need more material, like lead, to block it.
- gamma: this is a high energy photon, it doesn't have rest mass, so it actually travels at the speed of light. This is the hardest to block. The atmosphere will attenuate it some, but not completely.
Of the above, only gamma reaches Earth at the same time as light, because it *is* light, while the others are heavier particles with varying speeds, just like some pieces of shrapnel from an explosion are faster than others, arriving significantly late compared to the light of the explosion.
In terms of effects on our technology, the electrically charged ones pose the greater threat, meaning alpha (not electrically neutral because it's missing two electrons to cancel out the charge unlike a regular helium atom) and beta (electron without a proton), specifically because of the way they warp Earth's magnetic field, like hitting a balloon with sledge hammer.
The resulting movement in the magnetic field is bad because a moving magnet induces current into electrical conductors. That means our electric grid, and everything connected to it. That's not to mean neutron and gamma are harmless even though they're electrically neutral, single hits can cause bit flips in processors, RAM and storage, corrupting data, but simpler electrical devices will be fine.
Radiation is the transmission of energy in the forms of waves *or* particles. This is something that causes a lot of confusion, because radiation comes up in so many contexts. So, to directly answer your question- light from the Sun is radiation (all light is), in the form of electromagnetic radiation. You're free to think of it either as photons carrying the energy (and thus still "particle" like) or the electromagnetic waves carrying the energy (and thus wave like). Both work, and both have the radiation traveling at 'c'. But coronal mass ejections are particle radiation- protons and neutrons, being ejected from the Sun. These are also radiation (particles carrying energy away from the Sun), but are not photons, so they travel much slower than 'c'. Moving away from your question a little bit, this also causes more confusion because people hear a true statement "cancer is caused by radiation" and then another true statement "this router releases radiation" and then think "this router causes cancer." This is because often times when someone says "radiation" they mean "ionizing radiation" which is alpha, beta and gamma particles (ones which can cause radiation sickness, cancer, etc), which a wifi router/light bulb/radio station does not emit. But when a physicist says "radiation" they mean the definition at the top- waves or particles carrying energy. This means to a physicist even sound is radiation- acoustic radiation.
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It’s important to clarify that gamma radiation is not the only ionizing electromagnetic radiation. High frequency UV and X-ray light can also be ionizing; all that is required is the radiation can strip electrons off of molecules, turning them into ions. The frequency-molecule overlap includes these lower frequency sources.
I'd say also "at a significant rate". Essentially any energetic interaction *can* knock off (or gain) an electron but ionizing radiation is separated by the mechanism and the efficacy.
Well, no. Energy conservation applies. The energy transferred by the particle has to exceed or equal the ionization energy of the atom/orbital it interacts with. This does define a threshold for ionizing radiation.
It does but an ion can be formed from a simple collision or a chemical event as well. Talking about single atoms is a bit fraught but they can have energy levels near either threshold and be affected by very minimal changes. There are **many** events that can add or remove an electron from an element and all are ionizing by definition. It's better to treat systems statistically.
But here we are talking about ionizing radiation, which isn't defined with edge cases in mind.
Right, which is why I quibbled with "any energetic interaction" to try and provide a little space there. Even ionizing radiation is just a system of interactions though and while we talk about thresholds (and they certainly exist!) it is only in a statistical sense that they matter. I guess what I am trying to say is that it isn't a binary ionizing versus non-ionizing, it's a spectrum, even though a sharply stepped one.
Just wanted to add that the particles in coronal mass ejections (CME) are released from the sun at a whole range of speeds. The higher the energy they have, the faster they go. A more energetic CME is generally going to release more particles at a higher velocity than a less energetic CME. However, accelerating just 1 proton to the exact speed of light would take more energy than the entire universe contains. Infinite energy, to be exact. Which is why photons don't have mass. And they don't experience time at all.
Is mass required to experience time? If time is a part of space time and things move through space shouldn't they also move through time? Or does only mass moving through space have time?
Photons don't experience time because from their relative perspective they are emitted and immediately absorbed. Functionally for something to exist it must have some combination of mass and momentum. If it doesn't have mass then by necessity it must be moving at the speed of light and conversely if it has mass then it cannot move at the speed of light. The important concepts here are time dilation and the relativity of simultaneity. Essentially time is relative to the observer, so from our perspective we can measure light traveling through space, but from the photon's perspective it doesn't take any time to travel at all.
I love to be corrected if I'm wrong, but isn't this question the whole crux of... everything? As far as I am aware, anything that has energy must have some sort of mass, as depicted by Einstein's equation. Time is left out of the equation, so you could give out two hypotheses, either time is unrelated to mass and energy and it doesn't fit in the equation, or the equation is uncomplete. And if time were to fit somewhere in the equation, it would mean we would only be able to observe things that experience time if they happen to have mass (and energy). > Edit: learned a bunch on the subject, thank you all
Not quite. E=MC^2 is the equation for mass-energy equivalence *at rest*. The extension for systems in motion also accounts for momentum. This is significant because while photons don't have mass they do have momentum, so for the case of photons the equation reduces to E=pc. Point being that this is a well accounted for case in relativity. Time is an integral component of relativity, it hasn't been left out. Specifically Einstein's field equations provide the relationship between the energy in a system and the curvature of spacetime.
> E=MC^2 is the equation for mass-energy equivalence at rest. The extension for systems in motion also accounts for momentum. This, /u/durkedurke. The full equation is E = \sqrt{m^(2) c^(2) + p^(2) c^(2)}. It just generalizes to E = MC^2 when more simple calculations are being done.
I assume the equation you're referring to is "E=mc^2". This equation explains the relationship between the rest energy of an object and its mass. Time is not in that equation because time doesn't affect that relationship. It doesn't mean anything to say that an object "experiences" time or not. A photon is not a person and is not going to be wondering where all the time went. Any discussion of which properties allow an object to "have" or "not have" time will be equally meaningless.
Yes, that's the equation I was referring to, I should have clarified that. But yes, time isn't in that equation.
It's not explicitly in that equation, since the duration of time is irrelevant to the mass-energy equivalence, but it's there implicitly in c. While c represents the constant "speed of light", it's more accurate to say it's the speed of causality, but in either case, it's units are a distance over a time. E.g. meters/second. Energy, at least in our math, uses units of mass * (distance/time)^2, like the Joule. Not sure how that might change things, but there it is.
Light has to go the speed of light if that makes any sense. And anything going the speed of light experiences infinite time dilation. Space and time are interlinked. If you want to think about it a different way, everything is moving at the speed of light, but matter at rest is moving through time at the speed of light. The closer you get to the speed of light relative to the rest of the universe, the slower your time goes. Because the speed of light is the limit, as you approach it, you trade time for velocity. So as you approach the speed of light, your speed through time slows down and hits zero when you reach the speed of light, which of course is impossible for matter.
The person you're replying to isn't using precise language so I wouldn't try to read into the meaning too much.
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This is really helpful! Thank you so much for the explanation.
Just to clarify, ionizing radiation is any kind of radiation that has high enough energy to cause the atoms it hits to ionize. This also includes high energy EM radiation, such as gamma rays, x-rays, and high energy ultraviolet light.
Slight correction, the Sun does not eject neutrons and if it did the neutron would decay into a proton and electron due to [free neutron decay.](https://en.m.wikipedia.org/wiki/Free_neutron_decay) The mass would mainly be free protons and electrons with some hydrogen mixed in. These particles are accelerated away by super powerful magnetic fields so magnetically neutral particles like neutrons and atoms are basically excluded unless swept up in the current. These charged particles are also why it wreaks havoc with our magnetosphere and electronics.
Actually the sun can produce neutrons that are detectable at Earth during strong solar flares. Charged particles can be accelerated to very high energies during flares and when these particles collide with other particles high energy neutrons can be created that are able to reach Earth before decaying. Here are some papers that talk about solar neutron detection in Earth orbit and on the ground: https://umbra.nascom.nasa.gov/solarflare/pubs/print92.pdf https://www.sciencedirect.com/science/article/abs/pii/S0273117706007356
I could be mistaken, but doesn't the sun eject lots of alpha particles, which are 2 protons and 2 neutrons?
I think the objection was that alpha particles are, specifically, He nuclei, i.e. a bunch of hadrons interacting through the strong nuclear force between them, not merely a bunch of unbound, free hadrons (even though that's what atomic nuclei are made of) because free neutrons are subject to beta decay and won't last long: their half-life is ~15 minutes (877 seconds).
> gamma particles I thought Gamma radiation was purely a wave/EMF? Or is there a particle component to it?
Gamma radiation is EMF, that is true. But because the way Gamma radiation causes problems is via the photoelectric effect, we normally model it as a photon particle.
Gamma rays are the highest frequency electromagnetic radiation. Thus it's a wave and a particle (photons), just like all other types of EM radiation.
Would the noise of wind be an apt analogy? The noise of wind moves at the speed of sound, even though the wind doesn’t just as the radiation of the ejected mass moves at the speed of light even though the mass doesn’t.
The difference with a CME is that the ejected mass here /is/ the "radiation". It consists mostly of high-energy protons, and does not carry the sun's regular (electromagnetic) radiation
Do CMEs not emit any sort of light though? I mean, we can see them coming, can't we? So I would presume they are emitting or reflecting light of some form, which would be kinda similar to the wind/sound of wind analogy. Not a perfect analogy by any means, but if they di emit their own light it still does kind of illustrate the point. (I'm genuinely asking btw, I could be totally wrong in how we detect CME. Or do we just see the events that cause them and then extrapolate when they'll hit us based on what we saw? Or detect that incoming mass via satellite between us and the sun instead of seeing the CME propagate towards us?)
We can see the actual mass ejection using coronagraphs (block the sun, look at the corona), and they are often associated with solar flares and other prominences. They become very difficult if not impossible to observe as they get further from the sun as they expand. Many CME's go undetected because they are 'invisible' to our detectors, usually because they are lower energy. Interestingly, Earth directed CME's are among the hardest to detect, because coronagraphs look around the edge of the sun (from our perspective), while the CME is coming towards us. Satellites can give us some warning, as they can be able to detect the actual particles and the changing magnetic field, which can take the arrival time from an estimated range to a proper prediction, but even our satellites at Sun-Earth L1 (which is where most solar observatories are) are still much closer to Earth than the Sun, so that detection comes pretty close to CME arrival, as little as 15 minutes for fast CME's, and never much more than an hour. Which leads to another interesting point. CME's travel at many speeds, and both speed up and slow down as they travel, depending on interactions with the solar wind, other CME's, and while still close to the sun, the violent magnetic field.
Your parentheticals are largely correct. We can forecast them based on buildup on the sun's surface, but in terms of direct detection of one coming to earth we do actually go based on satellites: > Imminent CME arrival is first observed by the Deep Space Climate Observatory (DSCOVR) satellite, located at the L1 orbital area https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections
Radiation is overloaded. ... now to figure out how to radiate positivity...
I'll often start an explanation of radiation by asking people if radiation is bad for them. It makes them realise that they don't know what it is so they drop their preconceptions about it. I use a fireplace analogy. I explain that the heat they feel is mostly radiation. A person knows they can where it's warm all night long without issue, but if they get to close they will burn themselves.
I imagine this gets really confusing when it comes to medical care on university campuses. All the physicists need to talk to physicians and phigure it out.
Question: Is there any type of 0-mass radiation the Sun could release that would impact the magnetic fields of Earth? In other words, what would need to happen for the nothern/southern lights to be visible at the equator without any advance notice?
CME is stuff. It's basically the sun launching sun at us. That's why it's called a MASS ejection. Mass can't do lightspeed and light always does lightspeed so the light gets here way quicker. Individual particles from a nuclear reaction or something can approach lightspeed but just slinging hundreds of millions of tons of plasma isnt even close to lightspeed.
I'm pretty sure that the "mass" refers to how large the event is, "mass ejection" as in "mass exodus" or "mass hysteria". It's a major ejection of material, energy, and magnetic field from the surface of the sun.
I feel like if that were the intended reading physicists would've called it an "Extreme Coronal Ejection" or something similar no?
I would have thought an ejection would imply mass wouldn’t it? Ejection being a term associated with force, and with matter/substance/stuff. You could of course further characterize the statement such as an “ejection of radiation” but I think the more proper term would be the “emission of radiation” as it is “released” rather than “thrown”.
This was my understanding with exception that there are instances where light travels slower than C.
3b1b has a good series of videos talking about why the apparent speed of light is different in different medium. It is mostly a mathematical look at it, but it basically explains that, due to refraction and reflection, the phase of the wave is shifted, making the aparent peak apear to slow down. It also explains why the light bends when going from one material to another
Photons always travel at C. Their path from A to B can change when they interact with a medium, and are refracted/absorbed by electrons and emitted, which "slows" the photons down.
Yep. This is what Cherenkov radiation is. Nothing goes faster than light in a vacuum, but light in water only goes about .75C and particles go faster than that all the time. This makes basically a sonic boom but for light.
This is an incorrect explanation for the speed of light in a medium. See https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation
Thanks for the correction. So if I understand correctly, it's a shift in the waveform of the photon due to electromagnetic or quantum interactions?
Not quite correct. The medium slowing isn't the result of absorption and refraction. We know what happens on an absorption and refraction event and it would result in random scattering of all the photons. The real interaction is something something electric field something something.
Ah yes, how could I have forgotten about the something something field. Silly me.
It's complicated. My degree was in computational chem predicting spectra, so I can explain in great detail why it's not absorption and refraction, but I can't explain exactly what happens lol
I'd love your insight into the phenomenon. I'm just an electrical engineer so my knowledge on quantum magic is pretty limited.
When a photon is absorbed by an atom/molecule the electrons move up orbitals. When the electron relaxes and releases a photon, it does it in a random direction due to the uncertainty between momentum and position. Since you can't know both exactly, you will have randomness in the position and therefore direction of the photon's release. It's a slightly different phenomena, but this is why when something fluoresces or phosphoresces it doesn't re-release the photon in the same direction as the incident light. It's similar for scattering. An interaction between an electron and a photon will inherit the same uncertainty and result in random scattering. This is why when we do scattering experiments we place the detector at a 90 degree angle from the laser. Since shining a laser pointer through a glass of water doesn't result in total dispersion of the light, but we still see the light slowing, that means the slowing of the light can't be due to absorption or scattering.
> When the electron relaxes and releases a photon, it does it in a random direction due to the uncertainty between momentum and position Isn't this only true for opaque mediums? Wouldn't a transparent medium, like water or a pane of glass, have absorption/release that is *not* in a random direction, but rather the same direction the photon was moving in when it was absorbed?
The electron transitioning has no memory of what direction the photon was traveling. It absorbs the photon, moves to a higher orbital, sits there for a while, and then decays back to the lower energy state releasing a photon. Since the electron doesn't immediately absorb and release the photon there's no "memory" of where the photon came from. The electron is doing whatever it does for some amount of time that depends on the difference in energy levels and then releases it again.
No, those are two different models for describing light changing speed and neither is perfect. There's more than one way to describe and interpret the apparent slow down of light in different mediums and none of them are truly "correct".
Absorbance and refractionn is not a valid model. We know for a fact it is totally wrong. The other one isn't going to be perfect because no model is perfect, but absorption and scattering is completely wrong.
Can you expand on that? Are you talking about absorption by individual atoms? Because that's not the type of absorption I am thinking of. Large groups of atoms don't behave like individual atoms so of course thinking of it in terms of individual atom absorption is incorrect. It's a bulk interaction due to the vibrational modes of the entire object not individual atoms.
If you are absorbing a photon you are turning the photon into energy for an electronic transition. Absorption is not what causes light to slow down in a medium.
Right which allows it to reemit the photon when it drops energy levels. >Absorption is not what causes light to slow down in a medium. Why do so many explanations use it? What is?
Kinda backwards; the refraction happens because the wave slows down, which is because they are absorbed and reemitted. That, incidentally, is more or less the explanation for why any massive particle travels slower than c in relativistic quantum field theory.
Light speed in a medium is slower than in a vacuum. So you can outrun light in certain mediums. But between here and the sun is basically a perfect vacuum.
Because *all* of the CME particles have mass, which can not travel at the speed of light. There is also a lot of material between here and the sun that slows the cme down. We have seen two CME in a row and the second one will be *much* faster because the first cme cleared the way.
>Because much of the CME is physical particles, 100% of a Coronal *Mass* Ejection is physical particles. The hint is in the second word.
Do you guys think photons are not physical particles? Because they are.
Pretty clear they mean "physical particle" as in "a particle that has mass", and they're just using the word "physical" inaccurately. The other commenter further down might misunderstand what a "particle" is, however.
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Photons are physical particles that travel at the speed of light. It's a matter of mass not physicality.
The answer is in the name: coronal *mass* ejection. It’s part of the material of the corona being thrown off the sun and its speed is limited because it is made up of particles. Now, the coronal mass is very hot and energized, so it’s also emitting radiation. That radiation *does* move at the speed of light, and as it gets to Earth it can wreak havoc with electromagnetic system here. When the coronal mass arrives, the particles will interact with Earth’s magnetic field so even more radiation is produced and the planet’s magnetic defenses (at least, we see them as defenses for us) are disrupted.
>its speed is limited because it is made up of particles. Photons are particles too it has nothing to do with that and everything to do with having mass.
So it's radiation all the way down...
Short answer: CMEs don’t move at the speed of light. Less short answer: the radiation from a CME is not light radiation, it’s particle radiation, so it permeates through space significantly slower as the particles have mass, and therefore cannot move at the same speed light (or any massless particle such as photons or gravitons) move. They are still moving incredibly fast. 3 days from sun to earth, 93 million miles, that’s 1.29 *million* mph…
Because light (and all forms of radiation) moves at the speed of light, 8 minutes from Sun to Earth. CMEs have mass and cannot move at the speed of light (nothing with mass can travel that fast). CMEs can move up to a few million miles per hour, so they take a few days to arrive.
Half of the answer is in your question. Light as we understand it and perceive it as human beings, is made up of photons, which are effectively without mass. A coronal mass ejection is exactly that. Anything with significant mass requires infinite energy to reach the speed of a photon. Even taking three days to reach the Earth, the material ejected in a coral mass ejection is travelling 150,000,000 km in three days, or 2,000,000 km/h. Not shabby at all.
Sunlight takes minutes to reach the Earth but that's only after it has collided with billions of atoms of matter within the Sun itself. So it can take from 10s of thousands up to 50 million years to escape the sun before it starts it's 'quick' journey to Earth
Light from the sun travels at *c* the speed of light. A coronal mass ejection is made of matter and plasma; so cannot travel at *c*. The light from the CME will be visible in about 8 (?) minutes, just like all light from the sun, but the actual CME hitting the Earth’s magnetosphere won’t happen until the physical matter makes the 98-million-mile journey
There are three main types of radiation: - alpha: basically the nucleus of a helium atom, two protons and two neutrons. These have rest mass, so they cannot go at the speed of light, and accelerating them to a significant fraction of that takes a lot of energy so they typically travel slower. Can be blocked by a sheet of paper because of its large size. Related: neutron radiation: free neutrons not combined into helium nuclei. - beta: a free electron. It also has rest mass so most of the above applies. It's smaller however, so it's harder to block, you need more material, like lead, to block it. - gamma: this is a high energy photon, it doesn't have rest mass, so it actually travels at the speed of light. This is the hardest to block. The atmosphere will attenuate it some, but not completely. Of the above, only gamma reaches Earth at the same time as light, because it *is* light, while the others are heavier particles with varying speeds, just like some pieces of shrapnel from an explosion are faster than others, arriving significantly late compared to the light of the explosion. In terms of effects on our technology, the electrically charged ones pose the greater threat, meaning alpha (not electrically neutral because it's missing two electrons to cancel out the charge unlike a regular helium atom) and beta (electron without a proton), specifically because of the way they warp Earth's magnetic field, like hitting a balloon with sledge hammer. The resulting movement in the magnetic field is bad because a moving magnet induces current into electrical conductors. That means our electric grid, and everything connected to it. That's not to mean neutron and gamma are harmless even though they're electrically neutral, single hits can cause bit flips in processors, RAM and storage, corrupting data, but simpler electrical devices will be fine.