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.