Sunspots’ tangled tale: why the Sun has spots

Posted: December 30, 2016 by oldbrew in Cycles, Solar physics
Tags: , ,



We’ve ignored the early history and jumped in further on in this article about sunspots and the solar cycle. The astrophysicist author wonders if it will take another 400 years to figure out why the solar cycle (the period between magnetic reversals) is around 11 years on average. Maybe a few Talkshop posts could be helpful, dare we say?

What the heck was going on to cause these spots? In the early 1900s, a few key observations pointed astronomers and physicists in the right direction. For one, sunspot activity seemed to cycle every 11 years, from lots of sunspots to just a few-sunspots and back to lots of sunspots.

The cycle was even apparent during the weird “Maunder Minimum,” when there was very little activity in the 1600s (the term was coined much later). 

Then there’s the temperature. Sunspots look dark, but that’s only in comparison to the blazing solar surface around them; they’re cooler than the rest of the sun, but still ragingly hot in their own right.

Sometimes the sunspots are big, and sometimes they’re small, and they can last a couple weeks or a few months. Detailed observations of individual sunspots also revealed that these features were regions of superstrong magnetic fields. Researchers discovered this by measuring light released from hydrogen and helium in the sun.

The elements emit very specific wavelengths of light, called spectral lines. In the presence of strong magnetic fields, these unique individual wavelengths each get split into two very closely separated wavelengths. It’s called the Zeeman effect and has to do with quantum mechanics, and that’s all I’m going to say about that in this article. 

Finally, observers found that the sun’s own magnetic field would flip from north-south to south-north and back to north-south. These flips happen every — wait for it — 11 years. So the answer to sunspots surely has something to do with magnetic fields.

Spot the knot

The best sunspot solution scientists have so far is the Babcock model, so-called because a dude named Horace Babcock figured it out. It goes like this:

1) Start with a nice, regular, happy-go-lucky north-south magnetic field on the sun, all straight lines and everything.

2). The sun is not made of rock, or any other solid, so the star’s equator is able to spin faster than regions near the poles. This winds up the magnetic field, folding it in on itself and making it stronger, like doubling up rubber bands.

3) At the same time, the sun is boiling. Monstrous plumes of plasma rise up from the nuclear furnace below, reach the surface, cool off in the frigidness of space and then sink back down. This mixing further complicates the magnetic field.

4) Sometimes, the amped-up, rolled-up, coiled-up, twisted-up magnetic fields pierce the surface of the sun, creating an arch like a magnetic worm poking out of a plasma apple, to stretch an analogy.

5) Where the tube of magnetic fields pierces the surface, it prevents new, hot gas from reaching the surface, making that region cooler than average.

6) Have you ever tried twisting up a rubber band too much? At some point, it gives up and just snaps, which is the best way to explain what happens to a too-tangled magnetic field. After the snap, the sun “resets” to its usual, neatly aligned magnetic field, but this time flipped.

So there it is: Sunspots are features caused by a tangled-up solar magnetic field. That magnetic field goes from smooth to tangled every 11 years, explaining why sunspots have the properties and behaviors that they do, and why sunspot activity is linked to other magnetic events like flares and coronal mass ejections.

But why 11 years? Astronomers have seen “starspots” on other stars, and their cycles are all over the place. What’s going on in the sun to make its cycle 11 years, and not six months, say, or two decades? Maybe with another 400 years of observations, scientists will be able to figure it out…

Source: Sunspots’ Tangled Tale: Why the Sun Has Spots

  1. Richard111 says:

    No mention of “cosmic rays” and their effect on global cloud cover. Sunshine seems to be a rare feature of the climate these days in Pembrokeshire.

  2. oldbrew says:

    Richard: see below.

    ‘The flux of incoming cosmic rays at the upper atmosphere is dependent on the solar wind, the Earth’s magnetic field, and the energy of the cosmic rays’
    ‘…the strength of the solar wind is not constant, and hence it has been observed that cosmic ray flux is correlated with solar activity.’

  3. oldbrew says:

    ‘…nearly all of our previous estimates of the sun’s activity were inflated – the sun is 4 to 9 per cent less active than we thought.’

  4. Sparks says:

    The suns magnetic poles reversing is the cause of sunspots, the polarities interact on the solar plain, what causes the suns poles to reverse is the interaction it has with the planetary bodies in the solar-system.

  5. oldbrew says:

    Sunspots usually appear in pairs of opposite magnetic polarity

    The heliospheric current sheet [HCS] is the surface within the Solar System where the polarity of the Sun’s magnetic field changes from north to south.

    The HCS is ‘the largest structure in the Solar System’.

  6. Sparks says:

    Oldbrew Sunspots are caused by two polarities, it’s the sun’s poles reversing and interacting that is recorded as sunspots, you have the greatest discovery in modern human history right under your nose…

  7. p.g.sharrow says:

    To understand the nature of the Sun’s active surface you must first grasp Electro-Magnetic cause and effects caused by super heated metals in motion, electrical currents and the resultant EMF effects that are seen as sunspots and overall polar magnetics…pg

  8. Sparks says:

    Correct! p.g.sharrow… Can I say this, it’s like comparing a ball bearing to candy floss when the argument of scale between the sun and the planets comes up,..

    The suns mass consists mostly of hydrogen and its mass/density is enough to allow it to form a flowing polarity. The speed of the suns polarity reversals are regulated over time by its planetary bodies,

    To get back to the the scale fallacy, the suns poles are instant, the direction of the suns poles in the core of the sun occur instantly on the surface. Also planetary mass has the ability to knock it into cyclical behaviour.

  9. oldbrew says:

    And then there’s Jupiter with a magnetosphere 18,000 times stronger than Earth’s.

    ‘The Jovian (i.e. pertaining to Jupiter) magnetosphere is so large that the Sun and its visible corona would fit inside it with room to spare. If one could see it from Earth, it would appear five times larger than the full moon in the sky despite being nearly 1700 times farther away.’

    ‘Jupiter’s magnetosphere ejects streams of high-energy electrons and ions (energy up to tens of megaelectronvolts), which travel as far as Earth’s orbit. These streams are highly collimated and vary with the rotational period of the planet like the radio emissions. In this respect as well, Jupiter shows similarity to a pulsar.’

    Sounds like a lot of magnetism 😎

  10. Alan McIntire says:

    I’m surprised that Travis Metcalf’s idea was not addressed:

    “The Sun’s 11-year sunspot cycle is likely to disappear entirely, not just get less pronounced; [since] other stars with similar rotation rates show no sunspot cycles,” Travis Metcalfe, the paper’s lead author and an astronomer at the Space Science Institute in Boulder, Colo., told me……

    Bruce Dorminey , CONTRIBUTOR
    I cover over-the-horizon technology, aerospace and astronomy.

    Opinions expressed by Forbes Contributors are their own.
    future Sun, the authors note, is expected to not only have few if any sunspots, but also less coronal mass ejections
    Metcalfe thinks that there may even be a link to the onset of our Sun’s middle age and the evolution of life on Earth.
    The Sun has likely already entered into a new unpredicted long-term phase of its evolution as a hydrogen-burning main sequence star — one characterized by magnetic sputtering indicative of a more quiescent middle-age. Or so say the authors of a new paper submitted to The Astrophysical Journal Letters.

    Using observations of other sunlike stars made by NASA ’s Kepler Space Telescope, the team found that the Sun is currently in a special phase of its magnetic evolution.

    Heretofore, the Sun was thought to have been just a more slowly rotating version of a normal yellow dwarf (G-spectral type) star. These results offer the first real confirmation that the Sun is in the process of crossing into its magnetic middle age, where its 11-year Sunspot cycles are likely to slowly disappear entirely. That is, from here on out, the Sun is likely to have fewer sunspots than during the first half of its estimated 10 billion year life as a hydrogen-burning star.


    “The Sun’s 11-year sunspot cycle is likely to disappear entirely, not just get less pronounced; [since] other stars with similar rotation rates show no sunspot cycles,” Travis Metcalfe, the paper’s lead author and an astronomer at the Space Science Institute in Boulder, Colo., told me.

    The Sun has likely entered into a long-term period of magnetic inactivity, say Astronomers. (Photo credit YASSER AL-ZAYYAT/AFP/Getty Images)

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    Metcalfe says this transition takes a few hundred million years, but once the Sun completely crosses this Rubicon of middle age, it will remain magnetically inactive for the rest of its hydrogen-burning life.

    We now understand that every star goes through this phase, says Metcalf, and that the Sun has a peculiar magnetic cycle for its rotation rate because it is in the middle of the transition to a less magnetically-active state. And he notes that this new realization does help explain why the Sun’s current surface activity doesn’t jibe with patterns seen on many other sunlike stars.”

  11. Geoff Sharp says:

    Metcalf’s ideas are not relevant to our sun in my opinion. Our Sun so far is unique in that it is the only known star to have four outer planets with the right mass and distance that produces a reversal of solar torque, angular momentum and velocity.

    I suspect the known stars with exoplanets are not capable of solar grand minima as we know it. Most of the stars exhibiting a solar cycle are probably a result of tidal interactions as most stars with exoplanets have “Hot Jupiters” or are just a product of differential rotation.

    Our star so far is a one off.

  12. oldbrew says:

    Exoplanet hunters usually admit it’s much easier for them to detect planets that orbit close to their stars, given current methods and technology.

  13. leglise says:

    This seems to suggest that the astrologers maybe right. All those “crazy” in this house and over that orbit stuff suggest interaction between stars the planets and the sun and us. Isn’t this what is being claimed here? Do these guys of old know something we are just now rediscovering?