Sunlight and a spot of calcium

By Phil Plait | November 22, 2010 7:00 am

[Note: At the bottom of this post is a gallery of amazing pictures of the Sun from Earth and space!]

It’s so easy to take the Sun for granted. Too bright to even look at, we tend to think of it as a featureless white (or, misleadingly, yellow) disk, bereft of detail.

But then you see something like this, and it’s like a physical blow to your brain:

IBIS_CA_sunspot

[Click to get access to the massive 2400 x 2500 pixel version of this (once there, click the "download" link).]

Holy heliotropism. Seriously.

What you’re seeing here is small region on the Sun’s surface at incredible resolution. This image shows an area of about 200,000 by 200,000 km (120,000 x 120,000 miles), only about 0.5% of the Sun’s visible disk. Yet the detail is amazing! The full-res version of this image shows features as small as a couple of hundred kilometers across — bear in mind, the Sun is a whopping 1.4 million kilometers (860,000 miles) in diameter!

To give you an idea of what you’re seeing, take a look at that sunspot in the lower right corner. See the roughly disk-shaped dark inner portion of it? Yeah, that’s the same size as the whole frakking Earth!

Here’s a zoom of the sunspot, taken in a way to show more detail:

IBIS_FE_sunspot_detail

Holy wow! Sunspots are where the Sun’s magnetic field breaks through the surface. Plasma — that is, gas stripped of one or more electrons, allowing it to be affected by magnetic fields — under the influence of that magnetic field cools off, so it doesn’t emit as much light as the rest of the surface. That makes sunspots look dark in contrast, but if they were floating by themselves in space they’d actually be very bright (think of a flashlight in front of a spotlight if that helps). Look at all the tendrils and structure inside the spot; that’s all due to the way the gas is flowing under the influence of the tremendous heat of the Sun and its powerful magnetic field.

These images were taken with a very powerful camera called IBIS — the Interferometric BIdimensional Spectrometer — mounted on the Dunn Solar Telescope in New Mexico. The details of the detector are complex, to say the least (if you’re an astronomy engineering nerd then you can read this overview of it). The important thing is that IBIS can take images of the Sun at phenomenally high resolution both spatially (it can see tiny regions clearly) and spectroscopically (it can take razor-thin slices of the colors of an object). The former is important to see small details, of course, making the images above so spectacular. But the latter is critical scientifically, because different elements emit light at different wavelengths. Being able to sample those colors at extremely high resolution allows a vast amount of physics to be teased out of images such as this.

The orange color of the first picture is actually a bit of a cheat: the camera used to take it (see below) can examine colors in extremely fine slices, and this is a very narrow region in what is actually the near-infrared part of the spectrum (854.2 nanometers). That’s where the element calcium emits light very strongly, so in this image you’re seeing how calcium behaves on the Sun.

IBIS_FE_sunspotThe close-up sunspot picture was taken at a different wavelength, though — 543.4 nm to be specific — so it shows different structures, different details of the Sun’s surface. I’ve included the whole image here on the right (again, click it to get access to a hugely embiggened version). In it you can see the granulation in the Sun’s surface caused by gigantic convection cells; towering columns of hot plasma rising up from underneath the surface of the Sun. They cool and then sink back down, like boiling water in a pot.

Right now, the Sun is ramping up toward its period of maximum magnetic activity in 2013 and 2014. As the magnetic field gets stronger and more chaotic, we can expect to see more sunspots, and more associated solar flares and other vast explosions from its surface. I’m glad there are so many solar astronomers poring over images like these, trying to understand better the seething, roiling power of this mighty star sitting so close to us. We owe our entire existence to it, but it’s an uneasy relationship. The more we know, the better.



Here are some other amazing images of the Sun! Use the thumbnails and arrows to browse, and click on the images to go through to blog posts with more details and descriptions.

glennschneider_eclipse2010
alanfriedman_proms_halpha
alanfriedman_sun_halpha
atlantis_hst_2009may13crop
hst_wfpc_sun_610
iss_sunset
schneider_eclipse_plane
sdo304_dec62010
sdo_aia94_xrayflare
sdo_loopsflare
sdo_lunar_transit
sdo_prominence
sdo_solareclipse
stereo_flare
stereo_transit
sunpillar
sunspot_model
tenthings_sun_flare
thierry_iss_atlantis_2010
thierry_transit_iss

     

MORE ABOUT: spectrum, Sun, sunspots

Comments (38)

  1. The structure around the “dark” area of the sunspot always makes me think of looking at the edge of a cliff going down a deep hole. Is that what’s really going on, and the center of the sunspot is lower down, or is it just a figment of my imagination, and everything is basically “flat”?

  2. Messier Tidy Upper

    @ ^ Ken B : Well our Sun is round & not flat too you know! ;-)

    Seriously, I’m not sure. I would think the high gravity keeps things fairly level there but then we do have eruptions of material from the Sun – prominences, flares and Coronal Mass Ejections – and the circulation of the rotating and convecting solar layers so I’m unsure. The sunspots are certainly much cooler but lower – or perhaps higher – than the average solar surface? I couldn’t say.

    It’s so easy to take the Sun for granted. Too bright to even look at, we tend to think of it as a featureless white (or, misleadingly, yellow) disk, bereft of detail.

    We also tend to think of our Sun as an “average” star – and its really not.

    Our Sun is, in fact, in the top 5% of all stars with most stars being far cooler, fainetrand less massive red dwarfs (75% or so), orange dwarfs (15 % or so) or white dwarfs (another 10% or so). Less than 1 % of stars are types O & B, about 4% are types A, F, & G with the hotter “bluer”, more massive stellar spectral types being *much* rarer and rarer as you get to higher masses / temperatures.

    BTW. Those stats were pre-dating the “new” (yikes – over ten years old now methinks! :-o ) brown dwarf spectral types of L & T. So if they are counted as “stars” then it makes our Sun even more statistically impressive in that greater stellar percentage scheme of things. Info. via Ken Croswell’s article on ‘Is There Life Around Alpha Centauri’ in ‘Astronomy’ magazine circa 1990-ish. That was one thing that came as a revelation to me and stuck in my memory on reading so I’m relaying it on here.

    Our Sun is more impressive than we usually think &, yes, that’s a good reminder & neat image of its bubbling plasma surface there. :-)

    ***

    PS. Uh, sorry Phil but I’m not getting the solar images gallery appearing there. Could just be an issue at my end but thought I’d let you know.

    PPS. Okay – now the solar gallery’s there – never mind / thanks. :-)

  3. Chris

    All I can think of is the Eye of Sauron.

  4. James

    Phil,

    So the Sun is officially a White Dwarf then or are there no colors associated with the A,F,G, etc. designations. I’ve always heard it refered to as a G2V Yellow Dwarf even in scientific papers. If the G type stars are generally yellow from Earth then does that change their designation if you view them from space? Should we start a campaign to get people to quit painting the Sun yellow like nearly all artistic renderings?

  5. The X-ray flare makes me imagine the sun was involved in a long conversation with another star, and this was it’s way to say “Boo-yah!”

  6. I still love Alan’s pic from last month teh best. Really fantastic work.

  7. Gary Ansorge

    X ray flares are not so good for living things. I’m not sure how much protection we get from the ozone layer but since O3 absorbs ultraviolet I expect it’s also instrumental in blocking X rays. If our ozone layer was seriously depleted, would that allow for mutagenic effects from Xray bursts? Gee, maybe that’s how we managed to get bursts of new speciation,,,and extinctions.

    Great pics Phil. Tanks.

    Gary 7

  8. We need to start calling them Sun Flowers instead of Sun Spots. I know, I know…I’m being a girl – but come on – they look like flowers. And they are beautiful, which ‘spot’ just doesn’t really express. Spot sounds like a thing we should wash up.

    So, who do I go to in order to get this fixed?

  9. Also, Van Gogh could have painted the first picture.

  10. @ Ken B: “Is that what’s really going on, and the center of the sunspot is lower down(?)”

    Yup, it is, that’s the Wilson-effect or Wilson-depression. It’s not empty space aboce it of course just the material that emitted the light we see (“surface”) is below the surroundings by a few hundred kms. I dont know the details though, it has to do something with the balance between the gas pressure and the pressure of the magnetic field in the flux tube.

  11. Larry

    These pictures you post continually amaze me. I have one of the NASA ones from a while back as a possible wallpaper. This just says to me the Sun is a living, dynamic thing. It is hard to lost sight of that when it looks like a giant yellow-white ball in the sky.

    Non-Believer I agree, we they are like flowers and beautiful. I don’t think it’s a girl thing being able to appreciate the beauty. I am a guy and I see it. It’s the inherent beauty that first drew me to looking at the sky.

  12. That’s my desktop background sorted for a while. At least until I get tired at staring at my screen in awe each time I minimize all windows.

  13. Technogeek

    That last one is now the wallpaper on my Android phone.

  14. Old Rockin' Dave

    Forgive what some may count a dumb question, but where does the calcium come from? I always was taught that there was only hydrogen and helium, and that heavier elements came much later in the lifecycle of a star.

  15. Chris

    @12 Dave Hydrogen and Helium are the major constituents of the sun (93.96% and 5.919%), but the sun has all the other elements as well. They are present as impurities and came from the star that went nova before our sun was born. So our sun’s mother, if you will. That’s where all the Earth’s (and other planets’) heavy elements came from. Calcium is 0.00019% in the sun, but by filtering out all the other stuff, you can see much more detail since the intensity is less.

  16. Capt. Jerk

    Hypothetically speaking, If I was to travel close to the sun in a space ship and observed it through a clear, unfiltered shield, what colour would it be?

  17. Gary Ansorge

    Those new pics present something of fractal imagery to me.

    Maybe that’s just because I’m hung up on repeating patterns.

    Tile filling, anyone?

    Gary 7

  18. MadScientist

    That’s awesome – I’d worked with telescopes photographing the sun many years ago (with this thing called ‘film’) and I can guarantee that by the time I’d enlarged the print to a comparable size you certainly wouldn’t see that level of detail. I can’t even recall hearing of the Dunn Solar Telescope (though with the Pierce-McMath telescope at KPSO just a few hours out of Phoenix, I never had an inclination to look around for other solar obsevatories).

    I’d also like to point out that calcium is typically monitored at an ultraviolet wavelength (because it’s a line which is easy to isolate), but IBIS operates from ~orange to near-IR. It has an incredibly narrow bandwidth though at a mere 0.003-0.004 nanometers – a bit over a factor of 10 narrower than the best I had worked with (though that was over 20 years ago).

  19. Chris

    @16 The solar spectrum peaks in the green region, however the sun would be so bright if viewed unfiltered that you would probably see a flash of white then total blindness as you’ve just fried your eyeballs. That’s why the astronauts have that gold colored shield on their helmets.

  20. Ken B @ 1, lacalaca @ 10: The Wilson depression is a depression of the visible surface, or the location wherethe optical tau=1. With a more opaque plasma, tau=1 will occur higher in the solar atmosphere and with opaque plasma it will occur deeper. Now in sunspots there are strong magnetic fields which add a magnetic pressure to the gas pressure, but it is also in pressure equilibrium with the surrounding Sun which has very little magnetic pressure. The gas pressure inside the spot is therefore less than outside. This is accomplished by lower temperatures (the reason it is dark) and lower densities both of which result in a less opqaue plasma and hence the Wilson depression.
    Old Rockin’ Dave @ 14: From the pictures you could easily get the impression that calcium, iron and hydrogen is concentrated in those amazing filamentary and granular structures. That is, however, not the case. The solar plasma is throughly mixed by convection from the high atmosphere and down to a depth of ~0.3 of the solar radius (~200Mm). The structure in the pictures come (mostly) from the temperature sensitivity of the spectral lines that are used, together with the depth-range in the solar atmosphere that they sample. From that information we can learn a lot about the Sun.
    Cheers, Regner

  21. 19. Chris Says: “That’s why the astronauts have that gold colored shield on their helmets.”

    Not just gold colored, it’s real gold. It’s a shield a couple of microns thick that’s a good broad band absorber of EM radiation. The most important, for the astronauts’ skin, is absorbing the UV.

    I remember watching one of the last Apollo missions (16 or 17 when they had the rover) and the dust kicked up during travel got all over the TV camera lens. When ground control said they were having trouble seeing (especially when the sunlight would fall on the lens) one of the crew came over with the brush to clean it. To better see what he was doing, he actually raised his shield. Ground control started urging him to hurry up and put it back down due to the UV reflecting off the surface. To me, though, it was startling to see that there was an actual guy in there!

    Yes, we all know there were people in those suits, but with the reflective visors we tend to have a very impersonal impression of them, like they’re all Halo players or something.

    - Jack

  22. matt

    If you poked the sun (if you could) what consistency would it have? Would it be hard? squishy? What?

  23. DLC

    Oh Sure.. .you say a space shuttle and an orbiting telescope.
    Me, I see Russel’s Teapot and a sugar cube !

  24. sHx

    I remember watching one of the last Apollo missions (16 or 17 when they had the rover) and the dust kicked up during travel got all over the TV camera lens. When ground control said they were having trouble seeing (especially when the sunlight would fall on the lens) one of the crew came over with the brush to clean it. To better see what he was doing, he actually raised his shield. Ground control started urging him to hurry up and put it back down due to the UV reflecting off the surface. To me, though, it was startling to see that there was an actual guy in there!

    I wish I could see that footage. Now that would be a good blog entry for Bad Astronomy.

  25. Gary Ansorge

    23. matt

    It’s a big, hot, ball of gas so I’d expect it to have about the “consistency” of our atmosphere.

    One should however, be cautious about poking old Sol. It just might poke back,,,(if you look into the abyss,,,etc)

    Gary 7

  26. Joseph G

    @#23 Matt: It’d probably be very hot and burny :)

    In all seriousness, I’m not sure what the density of the “surface” of the sun is (the point at which the plasmas go from being more or less opaque to more or less transparent) but as others have said, it’d likely act just like any gas.

  27. Joseph G

    @#22 Jack: So THAT’S why Halo helmets are all reflectiv-ey. Who’d have thought there was a good reason? I thought it was just to look cool ;)

  28. Amazingly beautiful. Seriously inspiring. I linked to this post today in my blog, Astronasty. I won’t link it here because then my praise seems like spam.
    A constant reader and fan.
    Much respect!
    -DJ Busby

  29. Messier Tidy Upper

    @20. Regner Trampedach Says:

    Ken B @ 1, lacalaca @ 10: The Wilson depression is a depression of the visible surface, or the location wherethe optical tau=1.

    Thanks for that. :-)

    Now if I can just find out what the blazes is meant by ‘optical tau=1′ there .. Does that mean the particular level of solar surface or suchlike?

    @26. Gary Ansorge Says:

    One should however, be cautious about poking old Sol. It just might poke back,,,(if you look into the abyss,,,etc)

    Yeah, with a solar flare or Coronal Mass Ejection many times larger than the Earth! ;-)

    @23. matt Says:

    If you poked the sun (if you could) what consistency would it have? Would it be hard? squishy? What?

    Interesting question – I’m not really sure & will suggest that you ask it on the BAUT forum or send it as a question to one of the astronomy mags. :-)

    Guess it would depend on which part of the Sun you poke. We are already enveloped inside the solar wind and then there’s the diffuse but denser solar corona before you reach the various levels – the photosphere or visible surface, chromopshere, solar core, etc. Each part would probably have its own tactile texture impression getting firmer and more resistant -and hotter – with depth.

    The Solar surface is fairly dense so I’d guess it would fell pretty firm and solid but then its also rather liquid in nature with convection cells, bubbling plasma and so forth so, yeah, not sure. Except as folks have noted it’d be *HOT.* Very.

  30. Regner Trampedach

    MTU @ 30: My bad: a word fell out of my brain and onto the floor instead of the keyboard… It should read: where the optical depth, tau, is equal to 1. tau=1, is the definition of the visible surface of a star, the photosphere. It is the last scattering surface. The photons we see, most likely come directly from that depth, although there will be a distribution around it. (Field) Biologists will know of sighting depths in lakes, where a white plate is lowered into the water until it cannot bee seen any more – that is a measure of optical depth.
    Matt @ 23 and Joseph @ 27: The density on the solar photosphere is about 0.3 microgram/cm^3 which is the density of Earth’s atmosphere at about 60kms altitude (Mt. Everest is 8.8km in comparison!). The temperature there is about 240K, which is a tad on the cool side of the 5777 of the solar photosphere… It would be hot, hard to breathe and most of it would, of course, not be oxygen (only about one part in 2000 would be oxygen, mostly atomic, hardly any of it would be molecular O2 – we seem more comfortable with 21% O2). You might want a reflective space-suit with one of them gold helmets…
    Cheers, Regner

  31. Nigel Depledge

    Ken B (1) said:

    The structure around the “dark” area of the sunspot always makes me think of looking at the edge of a cliff going down a deep hole. Is that what’s really going on, and the center of the sunspot is lower down, or is it just a figment of my imagination, and everything is basically “flat”?

    I seem to recall seeing a pic of sunspots near the sun’s limb, and it was clear in this oblique-angle shot that the centre of the sunspot was lower than the rest of the chromosphere.

  32. Gary Ansorge

    31. Regner Trampedach

    “The density on the solar photosphere is about 0.3 microgram/cm^3 which is the density of Earth’s atmosphere at about 60kms altitude (Mt. Everest is 8.8km in comparison!).”

    Great answer. I KNEW there was a reason I liked this blog. So many competent people here.

    Tanks,

    Gary 7

  33. Messier Tidy Upper

    @31. Regner Trampedach Says:

    MTU @ 30: My bad: a word fell out of my brain and onto the floor instead of the keyboard… It should read: where the optical depth, tau, is equal to 1. tau=1, is the definition of the visible surface of a star, the photosphere. It is the last scattering surface. The photons we see, most likely come directly from that depth, although there will be a distribution around it.

    No worries & many thanks for explaining that. Much appreciated. :-)

  34. Amazing image!

    I wonder, if one were to be able to stare at the Sun, filtered in such a way to see that detail, how fast would the surface be changing?

    Would it be boiling and tumbling and forever moving rapidly or would these shapes be quite persistent for some time due to the huge masses of the shapes we are seeing?

  35. Amazing freakin blog here. I almost cried while reading it!

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