Could you focus light from Sol's corona?

[negativzero]

For instance, if you put a big "magnifying glass" above the atmosphere in the shadow of a total solar eclipse thus blocking out light from the "surface of the sun", could you heat an object to a temperature hotter than the surface of the sun? Applying the Second Law, one can't raise the temperature of a hotter object using the heat from a cooler object, not even by focusing light from the cool object with a magnifying glass. However, since the corona is typically at higher temperature than the surface, it seems feasible that one might be able focus enough of the coronal light to get more than 6000 K concentrated in a small spot. I'm assuming that since it's a total eclipse the radiation from the surface wouldn't dominate the spread of energies focused. I can't imagine what device would be used for such an experiment, or what the utility of it might be except perhaps to explode a tritium BB or something.

 

[sophiecentaur]

Hmm - that's an idea. The snag is that the temperature achieved would have to relate to a mean temperature over a full sphere. The optics to achieve that would be a bit taxing. For a start, the Moon, getting in the way, is far cooler than the body of the Sun. You could possibly do better without the eclipse and use the focussed radiation from the main body to 'blanket' the object that you wanted to heat up to more than 6000K.

 

[negativzero]

Sounds right. "Blanket"? Do you have a synonym?
I haven't thought about design. Assuming that one is projecting an image on a surface, it seems like it would a nice trick to somehow exclude any disc at all from appearing on the image. I have no idea how to bend light around corners but perhaps an object or series of objects and a series or cascade of light bends might shrink the appearance of any disc to a lesser significance. It also bothers me that i don't quiet get the significance of the "spread" of frequencies that make black body so important in heating. I assume coronal light is far from black body radiation, but I'm naive.

 

[sophiecentaur]

Sounds right. "Blanket"? Do you have a synonym?

The 'hot spot' would be losing heat not only back to the Sun - just as it will not be getting all the available heat from the Sun. If you surrounded the hot spot with a 'blanket' of his temperature then there would be less heat loss. That's an entirely practical comment.
About "black Body' radiation, you need to read about it to get the full story but the notion was studied way back by Lord Rayleigh and Jeans. If you take a cavity and allow it to fill with EM energy until it's in thermal equilibrium, you will end up with a balance of all frequencies, sharing the energy. The classical approach to this gave the answer that there would be more and more energy with increasing frequency (The Ultraviolet Catastrophe). Planck solved this anomaly by applying Quantum theory to the problem and produced a shape for the spectrum that achieves a balance between the energies at all frequencies. If you take an ideal cavity and make a small hole in it, the hole will behave like an ideal black body. And, of course, if you look into the hole and if the cavity is only at room temperature, it will look black because any light that gets into the hole will never get out. The cavity will look red / orange / blue-white, depending on the temperature of the cavity.
Do some Googling!

 

[russ_watters]

For instance, if you put a big "magnifying glass" above the atmosphere in the shadow of a total solar eclipse thus blocking out light from the "surface of the sun", could you heat an object to a temperature hotter than the surface of the sun?

No - the corona isn't opaque.

 

[davenn]

For instance, if you put a big "magnifying glass" above the atmosphere in the shadow of a total solar eclipse thus blocking out light from the "surface of the sun", could you heat an object to a temperature hotter than the surface of the sun?

ohhh my gosh, seriously ?

No - the corona isn't opaque.

yup, and it is also VERY tenuous ( low density), it also has a temperature of over 1 million K
and finally it's primary radiative mode is in X-rays ... the visible light output is relatively low in comparisonDave