Here comes the Sun(spot)!

By Phil Plait | June 17, 2009 12:39 pm

You’d think the return of blemishes on your face would be an unwelcome thing.

But if the face is that of the Sun, and the blemish is actually a planet-sized knot of tangled magnetic fields, then it’s actually most welcome indeed. Because now we’re starting to understand why they’re coming back.

Sunspots return in June 2009

After nearly two years of an acne-free surface, the first sunspots are starting to pop up on the Sun. Sunspots are regions on the Sun where the magnetic field lines of our nearest star erupt through its surface, and are an indicator of the amount of magnetic activity going on inside the Sun. Unlike a simple bar magnet, the solar magnetic field activity increases and decreases on a roughly 11-year cycle, and the number of sunspots follows in response. When the magnetic activity starts to rise after the cycle bottoms out, sunspots start to appear at a solar latitude of 22 degrees, and spread north and south from there.

Right now we’re at the bottom of the cycle, and sunspots are rare. But this two-year lack of spots has been the longest such period for nearly a century, and it’s had solar astronomers scratching their heads. That’s not too surprising, as the Sun is a fiendishly and vastly complex system of churning gas, and it’s numbingly difficult to observe and model it.

But astronomers have just made an important breakthrough in solar observations that links the way the gas under the Sun’s surface behaves with the way sunspots form. This is very cool and exciting news!

Imagine for a moment that I detonate a bomb under the ocean’s surface. This would cause a rising bubble of steam as well as a big displacement of water. By observing the way the water moves on the surface of the ocean, I can figure out a lot about how deep the bomb was, how big the explosions was, and so on. I don’t even need a bomb to do this, really; currents under the ocean’s surface distort the water above them as well, generating waves and motions that can reveal what’s going on at lower depths.

Same goes for the Sun! Using the Global Oscillation Network Group (GONG, a series of telescopes designed to study sound waves moving across the Sun’s surface) together with the space-borne Solar and Heliospheric Observatory’s Michelson Doppler Imager, astronomers can measure the way the surface of the Sun reacts to streams and movements of gas below the surface, allowing them by proxy to determine just how the gas deep inside the Sun behaves.

It’s been known for a long time that the Sun doesn’t rotate as a solid body; different parts of it spin at different rates. Underneath the surface of the Sun is a river of gas called the torsional oscillation, a jet-stream like movement located 1000 – 7000 km (600 – 4000 miles) down — for comparison, the Earth is about 13,000 km (8000 miles) in diameter, while the Sun is 1.4 million km (860,000 miles) across. This stream is actually located just beneath the Sun’s surface on this scale.

The flow of this gas has been linked to the solar cycle, but the connection has been difficult to determine. It’s known to form every 11 years near the Sun’s poles, then starts to slowly migrate down to lower latitudes. But now, using GONG and MDI, astronomers have been tracking it, and found that recently the migration has been more sluggish than average. Instead of taking two years to move about ten degrees of solar latitude as it usually does, in this cycle it’s taken three. This would explain why the sunspots have been delayed.

Moreover, their observations have indicated the first sunspots to appear on the Sun this cycle did so right when the torsional oscillation reached the "magic" latitude of 22 degrees! Since this is where sunspots always start to appear once the solar cycle starts to rise again, it clinches the connection between this subsurface jet stream and the formation of the magnetic fields that cause sunspots.

As Frank Hill, one of the astronomers who has been making these measurements, put it:

"It is exciting to see that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging at the new active latitude." Since the current minimum is now one year longer than usual, [Drs. Rachel] Howe and Hill conclude that the extended solar minimum phase may have resulted from the slower migration of the flow.

The reason this is important is that it’s extremely difficult to predict the sunspot cycle, and this measurement of the torsional oscillation gives us a handle on being able to do that — no other methods so far have been able to predict this long period of low activity. And that in turn is important because the Sun’s magnetic field is linked to solar activity: flares and giant coronal mass ejections, vast explosions of subatomic particles that can damage satellites and even cause blackouts on Earth (there may even be a connection between sunspots and climate and weather, although this is a very tenuous and difficult link to establish).

Being able to predict sunspots means being able to predict how our tempestuous Sun behaves, and that means possibly having early warnings about dangerous outbursts from the Sun. This can save billions of dollars worth of satellites and power grid infrastructure on Earth, and may even save lives (blackouts tend to happen when the power grid is under stress during the periods of coldest winter and hottest summer, when you really don’t want your power to go out).

We depend on the Sun for light and heat which make life on Earth possible, but the flip side of that is that we’re subject to its violent nature as well. But we’re making great strides in understanding the Sun, and this knowledge has gigantic practical implications.

Practical knowledge is useful (by definition), but I still reel at the idea that we can measure with confidence streams of gas that happen thousands of kilometers below the Sun’s surface, forever hidden form direct view. Incredible.

Actually, it’s credible. It’s science!

Solar image from NASA/ESA/SOHO.

CATEGORIZED UNDER: Astronomy, Science

Comments (48)

  1. Scott

    Okay, this is awesome, I which I knew enough about the Sun to make an intelligent comment, but with your explanation, this is so cool (or hot, or mixed?)

  2. Colin J

    Awesome. Been waiting for some solar activity to view. Been a quiet few years. Bring on the Northern Lights!

  3. Charles Boyer

    Sunspots also have a tie-in with our climate.


    “[T]he Sporer, Maunder, and Dalton minima coincide with the colder periods of the Little Ice Age, which lasted from about 1450 to 1820. More recently it was discovered that the sunspot number during 1861-1989 shows a remarkable parallelism with the simultaneous variation in northern hemisphere mean temperatures There is an even better correlation with the length of the solar cycle, between years of the highest numbers of sunspots. For example, the temperature anomaly was – 0.4 K in 1890 when the cycle was 11.7 years, but + 0.25 K in 1989 when the cycle was 9.8 years. Some critics of the theory of man-induced global warming have seized on this discovery to criticize the greenhouse gas theory.

    “All this evokes the important question of how sunspots affect the Earth’s climate. To answer this question, we need to know how total solar irradiance received by the Earth is affected by sunspot activity.

    “Intuitively one may assume the that total solar irradiance would decrease as the number of (optically dark) sunspots increased. However direct satellite measurements of irradiance have shown just the opposite to be the case. This means that more sunspots deliver more energy to the atmosphere, so that global temperatures should rise. “

  4. Now that’s interesting, particularly the torsional oscillation information (which I knew nothing of by the way). The complicated processes that go into branch like helioseismology really is incredible.


  5. As an amateur radio operator (VE3OIJ), I am looking forward to the reappearance of sunspots. With sunspots comes increased solar flux indices, and with that, long distance radio propagation on more days with higher frequencies.

  6. I wonder if anyone has looked into the possibility of analogous structures in the Earth’s core that might give rise to the behavior of its magnetic field.

  7. I saw a documentary on solar activity and solar storms. The sun is such an interesting astronomical structure. While we think it is stable and constant it actually undergoes series cyclic changes.

  8. OmegaBaby

    @#8 (Eric Salituro):

    Hrm…so some sort of much-weaker torsional oscillation inside Earth’s inner mantle to explain magnetic field reversals that happen every 250,ooo years?

    Interesting idea.

  9. Patrick

    I have an old astronomy textbook from the 50′s or 60′s that I picked up in a garage sale in my youth that mentions the sunspot cycle and its relation to radio interference and blackouts. It also mentions how the sunspot cycle is a total mystery. I have the urge to tape this article to that page for future reference.

  10. bigjohn756

    Maybe 10 meters will be more useful now.

  11. OmegaBaby


    I don’t think anyone doubts that the Sun can have a large impact on the climate of the Earth. However, stratospheric temperature measurements have been either steady or dropping since 1979. If those measurements are indeed accurate, then greenhouse gasses are really the only explanation for global warming. If the Sun were indeed responsible for heating of the troposphere, we would expect to see the entire atmosphere warming up, not just the troposphere.

  12. Reed

    Another interesting practical (?) impact of the late solar cycle. The C1XS X-ray Spectrometer on Chandrayaan-1 depends on x-rays from solar flares. Data so far has been limited, but hopefully it will pick up now and they can get good data in the extended mission.

    OTOH, if we had been able to predict the solar cycle years in advance, perhaps a different instrument would have been sent instead.

  13. Flying sardines

    @ # 2. Colin J :

    Awesome. Been waiting for some solar activity to view. Been a quiet few years. Bring on the Northern Lights!

    …. Plus the Southern lights or Aurora Australis too! ;-)

    We’re still a way off solar maximum though.

    Actually this is quite a relief, I gather a few folks (incl. scientists?) were starting to worry about us slipping into a new Maunder minimum – this is now NOT going to happen, right?

    Any idea yet on how this solar cycle is looking for strength … ?

  14. Torbjörn Larsson, OM

    How appropriate with a jet stream – I see that Gong Gong is a chinese demon (or water god) “responsible for the great floods”.

    Now I get curious. Googling, it appears that we can detect sunspots and some types of solar oscillations in other suns as well. Can this correlation (causation, actually) be seen elsewhere some day (well, night)? If so, I assume it would help modeling.

  15. Messier Tidy-Upper

    @ 10. Patrick Says:

    I have an old astronomy textbook from the 50’s or 60’s that I picked up in a garage sale in my youth that mentions the sunspot cycle and its relation to radio interference and blackouts. It also mentions how the sunspot cycle is a total mystery. I have the urge to tape this article to that page for future reference.

    Don’t tape anything to it, Patrick – you risk risk wrecking what could be a family heirloom! ;-)

    Just stick it inside the page …

    Actually I think a science text from that far back (pre-Voyagers, pre-Viking & MER*s, pre-Galileo, pre-Magellan**, heck pre-Lunar landings and even pre-Joh Glenn’s firts flight perhaps!) is likely tove very outated indeed scientificallyand proabbaly nota relibale source ontoo much except what we used to think … UInteresting sentimental value though!

    *= Mars Exploration Rovers
    Spirit & Opportunity

    ** = the spaceprobe Not Ferdinand! ;-)

  16. Every time I think about the sun, it boggles my mind. That we can even have a clue what’s going on that deep inside something that big…is pretty damned cool.

    Humans rock (because science rocks)

  17. I just read this book that says these sunspots will kill us all! PANIC!!!

    But even though the guy who wrote that book tried to cover all the ways death could come to us from the skies, he missed one: Mercury crashing into the Earth!

  18. IVAN3MAN


    Every time I think about [T]he [S]un, it boggles my mind. That we can even have a clue what’s going on that deep inside something that big… is pretty damned cool.

    Think about The Telegraph instead. ;-)

  19. Regner Trampedach

    Good post Phil! Wonderful to see some helioseismology on your blog :-)
    And what’s a factor of a 1000 between friends/astronomers… I am afraid that the Sun is only a puny 14,000 km across (700 Mm radius) – The Sun is only 109 times larger than Earth.
    The connection between the Solar jet-stream and the Solar cycle, is a fairly new one – previously we thought the cycle to be governed by what happened at the bottom of the convection zone, about 210 Mm below the surface. Click my name for a layman’s tutorial on helio- and astero-seismology.
    Regner (@ Mt. Stromlo Observatory)

    P.S. My next job just might be in Boulder – there are two other contestants…

  20. Cindy

    Glad the sunspots are starting to appear again. For the past two years I haven’t been able to have my Astronomy class observe sunspots (with a solar filter on the telescope). This year I even had to go to archive SOHO data for the rotation of the Sun using sunspots activity.

    Makes me want to go listen to the Police. “There’s a little black spot on the sun today….”

  21. You scared me, Phil! I keep a fairly good eye on Spaceweather:
    and I thought there was breaking solar news! But your image was from June 2nd!
    Had me going for a moment there…

    Good to know about the oscillation. Here all along I thought it was my fault for buying a PST… ;^)

  22. Bonesaw McGraw

    So when the sun is out of puberty the acne will be gone.

  23. fizzyb

    I’m such a geek for the sun that I immediately saw the picture and thought, “What’s Phil on about? That sunspot was earlier this month.” This was a fantastic article, though. I read bits and pieces of it earlier today via spaceweather, but really enjoy Phil’s take on it. Nice to have one more nugget of information regarding our star.

  24. I thought sun spots were made by Creationists throwing rocks at it.

  25. @IVAN3MAN:

    The telegraph also boggles my mind.


  26. Iain

    I’m a little confused. Do we have this data for previous solar cycles, or is this theory based off of a single set of observations?

  27. Stone Age Scientist

    Phil, thank you for this very educational post.

    Phil Plait for President of the United Federation of Planets!!! :)

  28. Bonesaw McGraw

    Nope, puberty. Thats why when the sun grows up and kills us all, it will become an adult. You’ll be able to tell because we will no longer exist, because the sun has only been watching our cartoons. When it doesnt find an interest in us, it will no longer need us and it will go somewhere else. DO YOU KNOW HOW IMPORTANT THE SUN IS?????!?

  29. Dave

    Nice post Phil!

    This explains the recent lack of sunspots. But I can’t help but wonder: why is the torsional oscillation moving more slowly than it has in the past?

    Obviously we’ve peeled one layer off the onion. But as it so often happens in science, understanding something poses even more questions.

    Isn’t science great!

  30. Ken

    Hhhmmmmmm. This ‘torsional oscillation’ measurem “explains” something?

    I’m skeptical:

    Why is the current going slower? And what makes “22 degrees” latitude “critical” (other than spots appeared there at the start of a recent solar cycle….NASA & others typically use 30 degrees lattitude as the upper limit for the appearance of new sunspots). NASA, for some reason, didn’t explain anything in this release.

    By the way, here’s a NASA press release from 2006 noting the slow “conveyor” within the sun:

    So what’s really new [as opposed to a new measure for the same thing] in this latest release? There may be something new there, but a real explanation of what it is isn’t provided.

    As for the underlying physics, Dr. M. Dikpati’s solar dynamo model basically addressed the same thing years ago (2004)–with explanations (for one of many such news releases on the model & its predictions, not to mention a number of published papers also available online, see:

    also see [from 2006]: — where they mention that this upcoming solar cycle will be delayed due to the slower flow). There’s a lot to be found, and explained, readily available using Dr. Dikpati’s name in internet searches.

    There are other very similar solar dynamo models are also published; their predictions & underlying physics are debated hotly (pun intended) by the folks that make & operate satellites — as that bunch of researchers try to prepare for solar activity in thier satellite designs & operations (this is big business — too much robustness designed in adds weight to the satellite & decreases capabilties, too little and it might fail in a solar event — ultimately this is money & profits — capitalism at work).

    In other words, this piece from NASA is exceptionally lame. There’s no explanation for the underlying physics given, the phyics described are not really new insights or explanations of anything — which means NASA has ballyhood what is in reality a new proxy measure for the same thing. For my tax dollars I expect more.

    And I’d expect the “Bad Astronomer” & JREF Pres. to see it for what it is: Nothing from NASA other than a puff piece of fluff to create the illusion that they’re on top of this scientific area.

  31. I find it very, very cool to learn that there is some predictability to the gas currents below the surface of the sun.

  32. DrFlimmer

    So. An answer is found for the “cause” of the sunspots. But, as usual in science, this raises a lot more questions (Ken has mentioned some):

    * What are these currents?
    * What causes them to move?
    * What causes them to reappeare every 11/22 years?
    * What can cause a delay?
    * Does the strength of the currents influence the number/power/size of the spots? Does it influence the strength of CMEs?

    I guess one can think of a lot more questions. Many secrets to reveal – science will never run out of work ;) That’s good news!

    However, the detection of the currents is good news, too. Now we have a tool to say when the spots will appear. And the detection of the current will lead to a deeper analysis in the upcoming solar cycle. I guess, the current will be watched carefully to see how it is related to the sun spots. Probably they will be able to find a connection between the current and a severe CME. THAT would be really good news, since this could lead to warnings before the CME actually erupts. We could save our technology far better with such a tool.

  33. KC

    >And I’d expect the “Bad Astronomer” & JREF Pres. to see it for what it is: Nothing from NASA >other than a puff piece of fluff to create the illusion that they’re on top of this scientific area.

    Looks like someone got up on the wrong side of the bed. You apparently didn’t read even the first line of the press release: “Scientists from the National Solar Observatory (NSO) in Tucson, Arizona…”

    This came from the NSO not NASA. And after all it is a press release – not a textbook…

  34. Robert Carnegie

    So now do we get a burst of really bad sunspots (which emit evil cosmic rays towards us, or something actually quite like that), or just the regular amount? And isn’t this just when we wish that the Earth’s magnetic field wasn’t collapsing (it’ll come back… probably?) Because it keeps the sunspot poison away.

  35. JustPassingThru
  36. Ken

    RE: KC Says — paraphrasing that remark that ‘this wasn’t a NASA press release’ … NASA might not have done the work, but, it DID sponsor the work & did provide the press release; the NASA press release for this is at:

    Also, Stanford’s Dr. Leif Svaalgard (an eminently qualified ‘solar scientist’) addressed this specific press release, and he didn’t mince words, at (scroll down or search to the first “Leif” reference):

    He comments regularly at that site to inject some objective science — and deserves credit for restricting his comments to the subject for which he’s most qualified.

    I just wished our “Bad Astronomer” picked up on what that release was really about and gave it the proper credit due, and no more….

  37. David

    An interesting bit of work, but I don’t understand how a one year delay in this sub-surface movement has produced a three year delay in the start of the cycle. In 2006, the main-stream prediction was for a year’s delay, but a very energetic cycle. Cycle 24 has finally started, but it certainly doesn’t look energetic.

  38. steve

    August 16 2009 36 days running no sunspots !

  39. Phil,

    It has been almost a year exactly. With the recent NASA news on sunspots, do you have anything new to add to this article?


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar

Login to your Account

E-mail address:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »