NASA's missions reveal the origin of theta auroras


The ESA/NASA Cluster and NASA’s IMAGE missions were in a position around Earth on Sep. 15, 2005, to determine how solar material in the magnetic environment in near-Earth space creates a special kind of high-latitude aurora called a theta aurora. Credit ESA/NASA/SOHO/LASCO/EIT

Auroras are the most visible manifestation of the sun’s effect on Earth, but many aspects of these spectacular displays are still poorly understood. Thanks to the joint European Space Agency and NASA’s Cluster mission combined with data from a past NASA mission called the Imager for Magnetopause-to-Aurora Global Exploration, or IMAGE, a particular type of very high-latitude aurora has now been explained.

Known as a theta aurora — because seen from above it looks like the Greek letter theta, an oval with a line crossing through the center — this type of aurora sometimes occurs closer to the poles than normal aurora. While the genesis of the auroral oval emissions is reasonably well understood, the origin of the theta aurora was unclear until now. A paper in the Dec. 19, 2014, issue of Science shows that hot plasma funneled into near-Earth space from the sun helps cause these unique aurora.

“The possibilities have been debated since the first satellite observations of the phenomenon were made in the 1980s,” said Robert Fear of the University of Southampton in the U.K. (formerly at the University of Leicester), and lead author of the Science paper.

Although separated by some 93 million miles, the sun and Earth are connected by what’s known as the solar wind. This plasma – electrically charged atomic particles – streams from the sun and travels across the solar system, carrying its own magnetic field along for the ride.

Depending on how this interplanetary magnetic field is aligned in relationship to Earth’s magnetic field, there can be various results when the solar wind arrives at near-Earths space. At the point where the two fields meet, Earth’s magnetic field points north. If the interplanetary field points in the opposite direction — south — then something called magnetic reconnection occurs, causing magnetic field lines pointing in opposite directions to suddenly realign into a new configuration.

The realignment opens the door so that solar wind material can funnel into the magnetosphere – the giant magnetic bubble surrounding Earth. This is what leads to the aurora, which is produced when the particles funnel down along Earth’s magnetic field lines and strike atoms high in the atmosphere. The interaction with oxygen atoms results in a green or, more rarely, red glow in the night sky, while nitrogen atoms yield blue and purple colors. Normally, the main region for this impressive display is the auroral oval, which lies at around 65-70 degrees north or south of the equator, encircling the polar caps.

But when the interplanetary magnetic field points northward, auroras can occur at even higher latitudes, sometimes resulting in theta aurora. Prior to the recent work, scientists suspected that theta aurora had something to do with the particles observed in the lobe regions of the magnetosphere. The plasma in the lobes is normally cold, but previous observations suggested that theta auroras are linked with unusually hot lobe plasma – but just how was unclear.

“It was unclear whether this hot plasma was a result of direct solar wind entry through the lobes of the magnetosphere,” said Fear. “Or if the plasma is somehow related to the plasma sheet on the night side of Earth. One idea is that the process of magnetic reconnection on the night side of Earth causes a build-up of trapped, hot plasma in the higher latitude lobes.”

The mystery was finally solved by studying data collected simultaneously by the Cluster and IMAGE spacecraft on Sept. 15, 2005. While the four Cluster satellites were located in the southern hemisphere magnetic lobe, IMAGE had a wide-field view of the southern hemisphere aurora. As one Cluster satellite observed uncharacteristically energetic plasma in the lobe, IMAGE saw the arc of the theta aurora cross the magnetic footprint of Cluster.

A theta aurora -- so named because it looks like a Greek letter theta, a circle with a line through the middle -- as seen by NASA's IMAGE satellite on Sept. 15, 2005. New research helps explains what causes these unique events. Credit NASA/R. Fear et al (2014)

A theta aurora — so named because it looks like a Greek letter theta, a circle with a line through the middle — as seen by NASA’s IMAGE satellite on Sept. 15, 2005. New research helps explains what causes these unique events. Credit NASA/R. Fear et al (2014)

The team found that the energetic plasma appeared on high-latitude magnetic field lines that had been closed by the process of magnetic reconnection driven by the northward pointed fields. This in turn caused the plasma to become relatively hot. Such observations support the idea that theta aurora are due to plasma trapped inside the magnetosphere, rather than material being directly pushed in from the solar wind.

“Solving the question of the origin of the theta aurora required Cluster’s high inclination orbit that sweeps over the region where the aurora are generated together with the imaging capability of IMAGE, which is no longer functioning,” said Melvyn Goldstein, Cluster project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Hopefully, future missions will give comparable capabilities to view the polar regions of the magnetosphere.”

Cluster consists of four satellites flying in formation around Earth. The data presented in this report were collected by Cluster-1. The Cluster mission was launched in 2000 and is still operating. IMAGE was launched in 2000 and concluded operations at the end of 2005. The data presented in this report were collected by the satellite’s far-ultraviolet Wideband Imaging Camera.


146 thoughts on “NASA's missions reveal the origin of theta auroras

  1. Confessions of a Reformed Greenhouse Denier
    Evidence supporting the theory of man made climate change is accumulating. Scientists previously from the Penn State University Center for Climate Studies have recently found from study of charred tree ring data that the incomplete burning of wood in the early 15th century had led to a reduction of man-made carbon dioxide leading to the dramatic cooling of the planet. Continued study of increased ice core thickness have led credence to the well accepted theory that possible wood shortages due to mans deforestation may have exacerbated man’s contribution to this decreased CO2 theory of cooling. Other scientific studies expected to be published in prestigious journals such as ‘Climate’ by scientists previously from other prestigious laboratories around the globe have supported the findings that there is 97% agreement in the scientific community of man caused cooling of the planet leading to the well documented ‘little ice age’ beginning in 1500 and lasting until the burst of industrial activity in support of the American Civil war began to rescue the planet from the grips of the serious cooling catastrophe.

  2. “Auroras are the most visible manifestation of the sun’s effect on Earth”
    I disagree. I think daylight is the most visible.

  3. The team found that the energetic plasma appeared on high-latitude magnetic field lines that had been closed by the process of magnetic reconnection driven by the northward pointed fields
    This is typical of the breathless press releases we often get. But it is old news. My adviser at the U. of Copenhagen the late Knud Lassen observed these aurorae extensively ~50 years ago [they were first observed much earlier in 1916] and showed that they occurred during reconnecting northward pointing fields, thus trapped and hot. BTW, the orientation of the ‘cross polar cap’ arcs depends on the polarity of the interplanetary field as it modifies the current systems in the polar cap [the Svalgaard-Mansurov effect].
    Here is one of Lassen’s publications on this

  4. I thought Thetans willed themselves into existence trillions of years ago. A lot of the Thetans around us are left over from when Xenu killed members of the Galactic Confederacy with hydrogen bombs. Or so Ron Hubbard tells us.

  5. This is interesting. I have read several explanations of various concepts of the earth’s magnetic field and plasma from the sun. One was from a paper by Leif which I believe was dated in the early 1970’s. I’ve been digging the ‘net on multiple occasions over the years to learn more.
    I hope this thread will bring forth some interesting comments. True science only please 😉
    So much to learn and so little time to learn it.

  6. It looks like a “No Entry” sign to me. The question is, what direction is it facing? Is it warning Earthlings not to enter space, or is it warning space travelers not to exit the galactic highway onto Earth because there are no services here?

      • What I find curious is that this phenomenon seems to happen more towards the equator of the sun rather than close to the poles, as on earth. Any perspective on this, Dr. Svalgaard?

      • Yet there appears to be no formal, mathematical definition of magnetic reconnection given in the Yamada paper. Perhaps I missed it, skimming rapidly through it. Where is “magnetic reconnection” formally defined?
        There’s a nice schematic on page 605, illustrating the concept of reconnection. But, IMO, that’s just the same as hand waving and talking about magnetic “lines” of force. Such lines are isopleths, like isobars on a weather chart. The lines don’t appear in a physical sense, but can be formally defined and are useful for understanding the underlying physics.
        I suspect it’s a lot like frontogenesis in meteorology. Weather “fronts” are hard to understand intuitively and difficult to “see” in the world around us. But they can be formally defined and detected numerically as deformations in pressure and temperature gradients.
        In fact the figure 3 on page 605 looks a lot like the deformations seen in frontogenesis. E.g. look at slide 8 in this lecture:
        Not surprising perhaps that magneto-hydrodynamics and meteo-hydrodynamics could be intertwined.

  7. “As one Cluster satellite observed uncharacteristically energetic plasma in the lobe, IMAGE saw the arc of the theta aurora cross the magnetic footprint of Cluster.”
    How energetic is “uncharacteristically energetic” plasma? In keV?
    Which direction is the acceleration in the transpolar aurora, toward earth or away from earth?
    What is the ionic composition of the theta aurora? Is it different from the oval aurora?
    Has there been a theta aurora during this solar cycle? Has there been an event since 2010?
    It looks interesting.

  8. There is no such thing as magnetic reconnection. Anyone who does Electrical Engineering specializing in electro-magnetics know this. Astro Physicists use this term because they don’t understand magnetic fields and they also don’t understand the nature of plasma.

      • Since plasmas are very good electrical conductors, electric potentials play an important role. The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the “plasma potential”, or the “space potential”. If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of “quasineutrality”, which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (n_e = \langle Z\rangle n_i), but on the scale of the Debye length there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths.

      • Of course Leif, “A plasma is electrically neutral, so elected plasma is not a current.”
        So that is why the heliospheric CURRENT sheet cannot possibly exist, right!?
        From NASA:
        From Hannes Alfven:
        Astrophysics and Space Sciences Library:
        LEIF SVALGAARD – this is getting very tiresome to hear you continually denigrate participants here who talk about electric currents in space, when I know that you know for a fact that there are electric currents in space! ….and not just the currents at the polar caps either.
        I suppose from your line of thinking that the ring current that Dst responds to doesn’t exist either!?

        • There most certainly can be currents in space. These currents are generated locally by changes in the magnetic field, e.g. across the heliospheric magnetic sector boundaries or charges bouncing back and fourth in the Van Allen belts through the varying strength of the geomagnetic field, or by magnetic reconnection. Anything interesting that happen is almost always due to large-scale electric currents, but the key insight is that those currents are consequences of changing magnetic fields.

  9. Θ, θ stuff is interesting . . . .
    It is nice to get away for brief moment from the earthly climate paranoia.
    Leif, a Happy Holiday Season to you. Thanks for your critique that helps in understanding the lead post.

  10. Normally plasma is a conducting medium of a neutral charge (equal amount of both types), but separation of incoming plasma charges takes place at the Earth’s magnetopause. From then on charges move within the Earth’s magnetic field, and doing so generate electric potential and electric currents.
    Two currents (one for each type of charge) are kept separate by the surrounding magnetic field, but can be forced together (‘short circuited’ releasing energy) by much stronger external field e.g. generated by incoming CME’s proton current (‘reconnection’ takes place at the far end of the magnetosphere’s tail, where the Earth’s field is much weaker); the event got mislabeled as ‘magnetic reconnection’

    • One way to disseminate nonsense is to mix it with something that is correct. You are a master at that. What you describe is not quite how it works and there is no mislabeling. Reconnection is the mechanism by which energy is fed into the magnetosphere and also the mechanism by which that energy is released. It is too tiresome to try for the umpteenth time to make you understand anything, so I’ll just refer to the links I have already given.

        • Here is an Xmas gift to you:
          Study the Introduction carefully:
          “Magnetic reconnection is a universal physical process that occurs in magnetized plasmas throughout the heliosphere and beyond, involving a change in the connectivity of magnetic field lines which changes the overall topology of the magnetic field. Magnetic reconnection between the interplanetary magnetic field (IMF) and the Earth’s magnetic field occurs at the Earth’s magnetopause and is the main mechanism for the transfer of mass, energy, and momentum from the solar wind into the Earth’s magnetosphere. This reconnection typically alters the topology of the magnetosphere, changing some magnetic field lines from a “closed” type, with both ends intersecting the Earth, to an “open” type, with one end connected to the IMF. This leads to an expansion of the polar cap—the enclosed dark region of the ionosphere poleward of the auroral oval—that almost exclusively contains open magnetic flux. Some of the open flux is ultimately reclosed by reconnection in the magnetotail…”

      • To return to the topic: in the “auroral oval—that almost exclusively contains open magnetic flux” the ‘almost’ refers to the existence of the theta aurorae that are on closed field lines.

      • Some dispute existence of magnetic field lines, one could google examples of opposing views, but as a practical engineer I have never came across one, so I am in the anti-camp. Presence of MF ‘lines’ imply discontinuity in between lines, unless they are infinitesimally closely spaced, in which case serve no purpose except as an aid to illustration or teaching; ergo in my view if ‘lines’ do not exist, they cannot reconnect, an effect that electric currents have no problem with.
        True, for the magnetospheric ‘reconnection effect’ two magnetic fields are required (lines or no lines), but only in the presence of electric currents, and as I gather from your link that is case in the lab too.

        • Only people who do not know what they are talking about dispute this. You can actually ‘see’ the lines, e.g.
          In a plasma, the lines are illuminated by matter frozen onto them. In that sense the field lines acquire reality by virtue of the plasma attached to them: move the plasma and the field line moves with it. Blow away the plasma into space and you get a solar wind with embedded field lines stretching across the solar system. An energetic particle [e.g. eject from a solar flare] will gyrate around the now real field line and follow it nicely.
          You have never lived inside a plasma so you will never have come across one. When field lines merge [because the plasma that carry them are pressed together] electric currents in a very small region are generated to allow the reconnection. Actually, what happens is that the infinite conductivity that the plasma has breaks down [particle gyration begins to overlap between the two regions with opposite magnetic fields] and a thin line or plane [depending on the geometry] develops electrical resistance, which is what allows the current to flow and removes the grip on the field lines the plasma had. All this is well understood and can be readily demonstrated in a laboratory setting and observed in situ in space. The willful ignorance you profess is no argument against the observational facts.

    • Leif Do you see the earth’s first line of resistance at the bow shock or at the magnetosphere
      The magnetopause [part of the magnetosphere] is where the two fields interact.
      But if your here to promote your own work , then I’m wasting my time
      I am NOT here to promote my own work. Just to tell the folks what we have learned the past 50 years.
      You waste your time reading the EU stuff. Here is one of the worst howlers:
      “the sun sends its charged plasma wind (solar wind) towards the earth. when it reaches the earth it is travelling at over 1 million kmh. on the earths nightside there is a region where the plasma wind suddenly goes into reverse and accelerates TOWARDS the earth at over 300 kmh.”
      Your links contains pure nonsense. Now, a lot of people are firm believers of all kinds of nonsense, so you are in good company.

    • is this why we are not drawn into the sun
      No, because our orbiting the sun has nothing to do with any electric field. Gravity, my friend, is balanced by the centripetal force of the sideways velocity in the orbit.

  11. Vukcevic
    Didn’t the experiment with a bar magnet ,paper and iron filings prove the existence of magnetic field lines. You might not see them with the naked eye but their there .

    • MF lines are ok for illustration purpose, since it may be difficult to visualise 3D geometry of the field otherwise, they are suppose to present gradual and not discrete change in the field intensity. If there were discrete field lines, hadron collider couldn’t work, since the discontinuity in the field would prevent precise focusing of the particle beams. Axial currents and magnetic field in plasma layers are not MF lines.
      Iron filing is turned into many individual tiny magnets which mutually attract (gather) and repel (remove) creating a standard ‘interference’ pattern. Boundary conditions are set by a paper sheet presence, not due to presence of any physical lines, since field around bar magnet is continuous, remove the paper and see all the ‘lines’ collapse.

      • Field lines are, of course, continuous and not discrete, but you ignore the fact that in a plasma things are different. The magnetic field is frozen into the plasma. And the plasma can be discrete [‘flux ropes’].

      • Flux ropes (also flux tubes) are not ‘lines’, they are three dimensional entities with electrically and magnetically predetermined cross-sections.

    • Genius of Nikola Tesla was in the extremely rare ability to visualise three dimensional magnetic fields and electromagnetic forces and their interactions with no aid of field lines or even paper sketches, which he only used as reminder the way many of us use our shopping list. Try to imagine field around simple bar magnet (ignoring lines from memory), after while my brain ‘hurts’.

  12. Powerful auroras are associated with geomagnetic storms.
    Unless there is a recent transpolar (theta) aurora, there is no way to look at other contributing variables – perhaps something could have whacked the earth’s magnetosphere.

  13. In a plasma, the lines are illuminated by matter frozen onto them. In that sense the field lines acquire reality by virtue of the plasma attached to them: move the plasma and the field line moves with it. Blow away the plasma into space and you get a solar wind with embedded field lines stretching across the solar system.
    yea, yea … as much as the cloud droplets get frozen and attached to isobars, with the westerlies blowing clouds and stretching isobars all across the Atlantic.

    • vukcevic
      December 22, 2014 at 5:36 am
      yea, yea … as much as the cloud droplets get frozen and attached to isobars, with the westerlies blowing clouds and stretching isobars all across the Atlantic.
      December 21, 2014 at 3:06 pm
      Only people who do not know what they are talking about dispute this. You can actually ‘see’ the lines, e.g.
      In a plasma, the lines are illuminated by matter frozen onto them. In that sense the field lines acquire reality by virtue of the plasma attached to them: move the plasma and the field line moves with it. Blow away the plasma into space and you get a solar wind with embedded field lines stretching across the solar system. An energetic particle [e.g. eject from a solar flare] will gyrate around the now real field line and follow it nicely.
      Picture is worth a thousand words Vuks.. Did you look at it?
      Wish we knew more about the solar Interplanetary Magnetic Field reconnection with the Interstellar Magnetic Field and how that might alter flow regimes through the solar system. Maybe the big dent in the front end of the heliosphere bubble will provide some clues.. Shifts in the gravitational focusing function of the sun..
      Couple of Earth directed solar CMEs or wind bursts (hits or misses) will mess around with the downwind helium/neon focusing cone that Earth should be orbiting through around this time of year.. Is nice to have a sunny day around these parts now and again..

      • Hi Carla
        And what is cross-section of those ‘lines’, hundreds possibly thousands of miles? a line has infinitesimally small cross-section.
        What is visible and what you see are not magnetic ‘lines’, they are (electric &) magnetic flux-tubs.
        Flux tubes are often associated with sunspots. FT exit photosphere into the solar corona it ‘arcs’ through corona and enters back into the photosphere.
        Again. what you see are not a magnetic ‘lines’ of any kind, but the walls of the magnetic flux tube (with cross-section hundreds possibly thousands of miles), they are vortices created by circulating electric currents.

  14. Leif
    I got this from a discussion you had on another thread on WUWT
    Leif Svalgaard
    September 2, 2009 at 1:55 pm
    Nogw (13:35:39) :
    And those Fe lines in sunspots’ spectrum?
    Very, very little magnetism come from Iron. For once, iron loses its magnetism above the Curie temperature of 768°C, and the Sun is hot. Solar magnetism does not come from iron, nor does that of the Earth. Both are generated by a dynamo, that rely on plasma movements to amplify an existing magnetic field. A good [and partly unanswered] question is where the very first magnetic fields in the Universe came from [if you say they were generated from currents, then the question becomes where the currents came from], but that is irrelevant for the everyday working of reconnection as we speak.
    But, again, this is not the place for discussing the pseudo-science behind the electric plasma thunderbolt universe. There are tons of websites that can mislead you to your hearts delight. But they do not belong on this serious ‘best science’ blog.
    Does the ion core become a negatively charged monopole magnet and emit negative charge Fe ion to space via the south pole which is the earth’s north pole and then reconnect .

    • Your comment does not make much sense as written. Gravity and magnetism are not related. If you can show they are, hurry to Stockholm to pick up your Nobel prize. The Earth formed from stuff that never has been in the Sun. I don’t understand you comment. I wonder if you do…

  15. Leif When I read Coulomb’s Law I see gravity as nothing more than magnetism at the nano scale. If Earth formed from a cloud of gas and dust and IRON was the first thing to for mass , wouldn’t the sun’s gravity drag it back into the sun because of the difference in temperature and mass, way before it formed earth the way we know it?

  16. It would seem that the significance of these data indicates that there is an Electrical component to the dynamic of the Universe….. I also see the scientific “language” beginning to reflect this, where once it was taboo.
    I am not forming an opinion or making a statement, I am simply remarking upon my observations.

  17. Leif
    When the sun is in a weak phase and doesn’t supply enough energy to earth’s core and it cools not by much does the planet shrink a bit . The result would be slight sea level rise , earth quakes , volcanoes going off and foul weather because more low pressure systems form . I see the earth like a capacitor, when the solar wind is strong earth stores energy and we get more high pressure systems and good weather. And when it’s weak earth releases energy low pressure and what we see is more foul weather .

    • The Sun doesn’t heat the Earth’s core significantly and any variation with time is completely damped out anyway as heat slowly, slowly makes its way inwards, so no geo effects are to be expected and certainly not on any time scales we care about. Time you read some of them books… 🙂

  18. “I am interested as I have been a small part of this …. working on communicating with submarines by modulating the power grid …”
    I think Dr S may be speaking about the ZEVS 82 Hz ELF transmitter. It requires a very large antenna. Location Murmansk. The Russians can communicate with subs all over the world.
    Why don’t you all behave.

  19. At some stage Zeke the truth will come out. And Anthony’s site is about relaying the truth not like some other propaganda sites like the jokers over at Skeptical Science
    Propaganda is information that is not impartial and used primarily to influence an audience and further an agenda, often by presenting facts selectively to encourage a particular synthesis, or using loaded messages to produce an emotional rather than rational response to the information presented.

  20. Leif,
    If you are still hanging around here I want to thank you for your links in a comment above. As a result I have been doing a lot of reading.
    I don’t know the answers to a lot of things I’ve read but I appreciate the discussions presented on this thread.
    One question that I have though. Has anyone considered that as the Earth has a magnetic and gravitation field and as with the case with the sun, could there be a similar case with something deeper “in space” that has not been quantified/qualified? The elliptical orbit of the Earth would suggest a strong possibility of a gravitational force “out there” somewhere. Magnetic fields and associated electrical fields have been discussed on this thread as well as elsewhere. Perhaps gravitational attraction/fields are all possibly related in some manner.
    So many questions, and so little time from a limited perspective in one man’s lifetime.
    Merry Christmas to all here and I look forward to your contributions in the New Year!

  21. I wish to know more about the reason for the (+) charge on the dawn side of the magnetosheath vs the (-) charge on the dusk side. I am referring to the most interesting paper by you dated 1973 I am currently looking at figure 4 (a) and (b).
    Some questions: 1) Is this entirely the result of the solar wind and why? 2) Does the effect of the Earth orbit around/through the sun’s interplanetary magnet field cause/affect this polarization of the charge? Please elaborate to resolve where you may feel I am losing the plot here if that may be the case. There are others but I just wanted to get this post out before the thread closes. I have spent a week trying to fully grasp what’s happening.

      • Leif,
        Thank you for responding. With regards to the structure of the charge in the magnetosphere, the question that I haven’t been able to grasp is: why is the positive charge located at the dawn side of the earth?
        As far as the light issue, the more I read the more it seems no one else really knows. I’m still stuck on a spiral trajectory of particles or energy packets. With spiral trajectories and those possibly overlapping/interlocking (in a sense, think spiral wound springs meshed together or in very close proximity with the spiral of the spring being the trajectory of photon) between individual rays could possibly explain the ability of light seeming to bend around an obstacle as particle repulsive charge/energy after passing a barrier may be the mechanism for that. Hell I don’t know, just a thought that keeps bouncing around in my head for years.

        • Charged particles [solar wind] traveling through a magnetic field [Earth’s] are deflected, positive charged one way and negative charges the opposite way. Given the directions of the solar wind and the Earth’s magnetic field leads to positive charges being deflected towards the dawn side [Figure 1 of my link]. A much more technical explanation can be found here:
          Light does not travel in a spiral [except near a black hole]. And light is a well-understood phenomenon. [Please] read up on the subject.

  22. Leif,
    I have been following the link you offered to . It is an excellent source and so many related links within leading to others and that has kept me occupied for a week.
    So many links and then ‘google’ expansions has somehow led me to the question I have of “What is light?” I have followed many ‘google’ links and currently have 7 open tabs on the subject. There seems to be some question as the whether light is a particle or if it is a wave. I have some idea that it is both. Perhaps particles traveling in a spiral trajectory being influenced by forces of gravity, magnetism, and charge attraction and repulsion all at the same time. Is there a good source to review the discussion/research on this? Note that I’m way past the discussion of the spectrum of wavelengths.
    The question of “what is light” has plagued me for years so any help answering this would be greatly appreciated.

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