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NASA's Solar Dynamics Observatory (SDO) observes and images the sun at ten different wavelengths. On January 22, this image was released in an article describing those wavelengths and what they tell us about the sun. You can access the article here. Previous diaries have been written about SDO. Links to some are provided at the end. This diary is about the information provided by each of the specific wavelengths used to observe the sun and how you can easily access it yourself.

When you view the sun with your eyes or a normal camera, you are seeing a spectrum of colors from red to violet. You may remember roygbiv from school. The sun's output in this visible spectrum peaks around yellow. Our eyes are also most sensitive to that. However, this visible spectrum is but a small part of the very wide ranging electro-magnetic spectrum. The sun radiates in an extremely broad range of wavelengths. Each comes from a different set of dynamics taking place on the surface and in the atmosphere of the sun.

More about the electro-magnetic spectrum and what those wavelengths reveal about the sun.



The E-M spectrum is composed of a continuum of wavelengths from the long radio to the very short gamma. All E-M waves regardless of wavelength travel at the speed of light through space. The product of the wavelength and frequency of the waves equals the speed of light. So, long radio waves have a low frequency. Short gamma waves have a high frequency. Another aspect of E-M waves is their energy. Energy is proportional to their frequency. Hence, high frequency gamma waves are very energetic and dangerous. Low frequency radio waves are less energetic and not dangerous. We are constantly bombarded by them from terrestrial and outer space sources.

The surface of the sun is basically a hot gas at a temperature of ~6,000 Kelvin. Kelvin temperatures are scaled from absolute zero and are 273˚ higher than Celsius temperatures. Hot gas at that temperature emits yellow-green light. Solar flares from storms on the sun can reach temperatures of 6,300,000 K and emit light in the extreme ultraviolet, invisible to our eyes. But, instruments on the SDO spacecraft do see it, and many others invisible to our eyes. As a result of these observations, scientists assign unique colors to the data output from the instruments to distinguish them from each other.

Not only does the sun contain many different atoms – helium, hydrogen, iron, for example -- but also different kinds of each atom with different electrical charges, known as ions. Each ion can emit light at specific wavelengths when it reaches a particular temperature. Scientists have cataloged which atoms produce which wavelengths since the early 1900s.

SDO scientists chose 10 different wavelengths to observe for its Atmospheric Imaging Assembly (AIA) instrument. Each wavelength is largely based on (one or two types of ions). Each wavelength was chosen to highlight a particular part of the sun's atmosphere.

Listed are the wavelengths SDO observes. The order is from the sun's surface and higher up into the atmosphere. The wavelength unit is Ångström. (1 Ångström = 10-10 meter)
Wavelength Information Collected
4500 Visible light showing the sun's surface or photosphere. ~6000 K
1700 Ultraviolet light from the surface of the sun and a layer above called the chromosphere. ~4500 K
1600 Emitted by carbon-4 to top of the corona. Temps increase rapidly. ~10,000 K
304 Emitted by helium-2 from the chromosphere and transition region. ~50,000 K
171 Emitted by iron-9 showing the quiet corona and coronal loops, ~600,000 K
193 Emitted by iron-12 at 1,000,000 K and iron 24 at 20,000,000 K. Iron-12 is at a hotter region of the corona. Iron-24 is a hotter part of a solar flare.
211 Emitted by iron-14 at 2,000,000 K. Hotter and magnetically active parts of the corona
335 Emitted by iron-16 at 2,500,000 K. Also hotter, magnetically active regions in the corona
94 Emitted by iron-18 at 6,000,000 K. From parts of the corona during a solar flare.
131 Emitted by iron-20 and iron-23 at greater than 10,000,000 K. These temperatures come from material in solar flares.

You can view the output from these ten instruments at any time. The instruments obtain several images every minute. Click this image to be taken to the web site. Note the red arrows in this image. Once at the Sun Today web site, hover your mouse over any of the wavelengths to view the current image of that wavelength.

From the SDO Mission Statement...
The scientific goals of the SDO Project are to improve our understanding of seven science questions:
  1. What mechanisms drive the quasi-periodic 11-year cycle of solar activity?
  2. How is active region magnetic flux synthesized, concentrated, and dispersed across the solar surface?
  3. How does magnetic reconnection on small scales reorganize the large-scale field topology and current systems and how significant is it in heating the corona and accelerating the solar wind?
  4. Where do the observed variations in the Sun's EUV spectral irradiance arise, and how do they relate to the magnetic activity cycles?
  5. What magnetic field configurations lead to the CMEs, filament eruptions, and flares that produce energetic particles and radiation?
  6. Can the structure and dynamics of the solar wind near Earth be determined from the magnetic field configuration and atmospheric structure near the solar surface?
  7. When will activity occur, and is it possible to make accurate and reliable forecasts of space weather and climate?

A very comprehensive series of diaries about SDO and related topics was written by my friend palantir for SciTech in June 2011. I highly recommend these if you want more information.
 Sun er Tuesday Science Videos Solar Dynamics Observatory
 Sunday Science Videos 8 Living With A Star
 Sunday Science Videos 9 Solar Dynamics Observatory Finale

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Originally posted to SciTech on Tue Jan 29, 2013 at 08:10 AM PST.

Also republished by Community Spotlight and Astro Kos.

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