onsdag 21 juli 2010
Can You See the Earth on the Surface of the Sun?
We all know that the Sun is clearly visible on the surface of the Earth, because the Sun is big and very hot.
In a discussion about backradiation, one may ask if the Earth is visible on the surface of the Sun, recalling that the Earth is small and lukewarm.
A rough calculation shows that the Earth blackbody radiation at surface of the Sun has to compete with a radiation intensity which is almost 10 orders of magnitude bigger.
A sensor resolving 10 orders of magnitude requires a resolution to atomic scales, which seems beyond what is thinkable. Just a reflection stimulated by a comment to the post Clouds as Retailers of Heat Energy.
We learn that it is easier to see a hot blackbody from a cold blackbody, than a cold from a hot.
This is because the high frequency signature of a hot blackbody is visible against a cold low frequency background, while the low frequencies of a cold blackbody disappear into a hot background.