Extreme Ultraviolet Wavelength Question

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On the Solar and Heliospheric Observatory (SOHO), a satellite which observes the sun from the First Lagrangian Point, there are 4 different Extreme Ultraviolet Imaging Telescopes, each with a different wavelength:

171 Angstrom - 1 million degrees Kelvin
195 Angstrom ~1.5 million degrees Kelvin
284 Angstrom - 2 million degrees Kelvin
304 Angstrom - 60,000 to 80,000 degrees Kelvin

For 171Å, 195Å, and 284Å, you can observe the pattern of rising temperature corresponding to higher angstroms. Contrarily, 304Å is meant to view a much lower temperature, despite a higher angstrom than the previous 3.

Additionally, I always thought that the longer the wavelength, the cooler the observed material would be, which contradicts 195Å and 284Å observing hotter material than 171Å.

Clarification of this would be greatly appreciated.

Source: http://sohowww.nascom.nasa.gov/data/realtime/image-description.html" [Broken]
 
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  • #2
davenn
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why would you say 304Å is meant to look at a lower temp.
The web site ( my daily favourite place to visit... I have been saving images from there almost since SOHO was established) tells you why 304 is hotter, its higher in the atmosphere.
there's a secret here that you may not be aware of....
The chromosphere (coronal region) is substantially hotter at millions of K compared to the ~ 6k K of the photosphere ( the sun's surface)

A little bit from Wiki to get you started on some personal research.....

The coronal heating problem in solar physics relates to the question of why the temperature of the Sun's corona is millions of kelvin higher than that of the surface. The high temperatures require energy to be carried from the solar interior to the corona by non-thermal processes, because the second law of thermodynamics prevents heat from flowing directly from the solar photosphere, or surface, at about 5800 K, to the much hotter corona at about 1 to 3 MK (parts of the corona can even reach 10 MK). The amount of power required to heat the solar corona can easily be calculated, that one required to balance coronal radiative losses and the thermal conduction toward the chromosphere through the steep transition region. It is about 1 kilowatt for every square meter of surface area on the Sun, or 1/40000 of the amount of light energy that escapes the Sun.....
It continues on further but I will let you do some discovery :)

Its an awesome topic and one I have been into since I was a kid doing my first sunspot drawings

cheers
Dave

PS ... The 304Å HeliumII is a good one to keep an eye on it shows the awesome prominences hanging above the sun :)
 
  • #3
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Please re-read the numbers I have posted (which are taken from http://sohowww.nascom.nasa.gov/data/realtime/image-description.html" [Broken]):

171 Angstrom - 1 million degrees Kelvin
195 Angstrom ~1.5 million degrees Kelvin
284 Angstrom - 2 million degrees Kelvin
304 Angstrom - 60,000 to 80,000 degrees Kelvin

60,000 to 80,000 degrees Kelvin is cooler than 1 million, 1.5 million or 2 million degrees Kelvin.

Yet the angstroms appear to increase with temperature except for 304, where instead of being a higher temperature, it is instead a lower temperature.
 
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For those interested, I seem to have found an answer to my own question (feel free to correct this if it is wrong/inaccurate):


The following information is found at http://web.williams.edu/astronomy/jay/solarlinks":
a) Helium II (that is, ionized helium, given that He I is neutral helium) at 304 Å. It shows gas at temperatures of about 60,000 K. (Note that K stands for kelvin, a unit using Celsius degrees but starting at absolute zero, –273°C. Since temperatures we are discussing are in the thousands or millions of degrees, we can ignore for our purposes the differences between K and °C.)

b) Iron IX (that is, iron that has lost eight of its electrons) at 171 Å. It is at a temperature of about 1,000,000 K.
c) Iron XII (that is, iron that has lost eleven of its electrons) at 195 Å. It is at a temperature of about 1,500,000 K.
d) Iron XV (that is, iron that has lost fourteen of its electrons) at 284 Å. It is at a temperature of about 2,000,000 to 3,000,000 K.

It seems that the extreme ultraviolet telescopes are viewing the emission spectra of different atoms, and that their emission wavelengths correspond to the temperature of that specific atom at those temperatures.

Thanks to http://www.sciencechatforum.com/" [Broken] for help with the answer.
 
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  • #5
davenn
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exactly right :)

yeah sorry I didnt read your original comment correctly. thanks for pointing that out ;)

and I also forgot to comment that the first 3 were ionised iron and the 4th (304) was
different element ie. heliumII
that was more relevent than anything else

Dave
 

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