• Question: If the sun is so hot no one can go near it, how do scientists know the temperature of the sun

    Asked by bekhitmm01 to Donna, Jo, Mark, Stuart, timcraggs on 17 Jun 2010 in Categories: . This question was also asked by kieranbrimicombe.
    • Photo: Joanna Buckley

      Joanna Buckley answered on 17 Jun 2010:

      Great question and to be honest, it’s a bit of guess-work, bekhitmm01.

      As you rightly said, we can’t pop a temperature probe on the sun. We would frazzle waaaaaay before we got there. And with our current technologies it would take ages to get there so it’s a lose-lose situation eitherway.

      We know how much energy the sun produces on earth over a specific area and we can measure this. We also know the approx distance to the sun so we can estimate how much energy it gives out and therefore how hot the sun is. There are other methods but they all give fairly similar answers.

      Wouldn’t it be cool to build a suit that we can wear which would be suitable for walking on the sun? Imagine that? Do you think this would ever happen? Would we be able to survive the 5500 °C surface temperature?

    • Photo: Donna MacCallum

      Donna MacCallum answered on 17 Jun 2010:

      You guys are definately keen on keeping us hopping between subjects!

      The sun is too hot for us to directly measure it’s temperature. However, scientists have been able to indirectly measure the temperture based upon the wavelength of light emitted from the sun and also from something called flux.

      This is really not my area of expertise, but I’m sure that Mark will be able to explain this much better!

    • Photo: Mark Lancaster

      Mark Lancaster answered on 17 Jun 2010:

      We know that the wavelength (colour) of light emitted by a body is related to its temperature hence phrases like red-hot and white-hot… the hotter the object the more it emits blue light and the cooler red light – so as something is heated up it will emit red-light when its coolest then yellow then green then blue such that when you add all these together you get white – so white-hot is hotter than red-hot – this extends beyond the visible spectrum – “hotness” is just a measure of energy and so if you go to lower and lower wavelengths ie higher and higher frequencies then you get more energy as in X-rays and ultra-violet light. This shows the wavelengths of the radiation emitted by the sun – it peaks close to the green/blue wavelength (at 500 nm). Wien’s Law relates the wavelength and temperature as : Temperature (in Kelvin) = 0.0029 / Wavelength (in m). The peak wavelength is at 500nm, so that gives 5,800 K.

    • Photo: Tim Craggs

      Tim Craggs answered on 17 Jun 2010:

      That is an excellent question, and not one that I know the answer to (though Mark probably does!). However, I think it is possible to tell how hot the sun is by the different wavelengths of light that it gives off. This is true of other stars from far off galaxies too.

      Just as an interesting thought – (and having just read Mark’s answer!) – I wonder if leaves are green because the sun’s maximum emission occurs in the green (500 nm). This would make green the best colour for absorbing the energy from sunlight!

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