It is true that flat-black materials are the strongest radiators. If you know the reflectivity of a material, you can measure its temperature from the flux of light (or infrared, for normal conditions) emitted per unit area from its surface. For a given temperature, the higher reflectivity will emit less. Even if you don't know the reflectivity - say, if you're taking an aerial or satellite photo - you can still measure the temperature by using a spectroscope to find the wavelength (or color) of the emission peak. As materials grow warmer, their emission grows both brighter and bluer. Thus hot stoves glow deep red, while lightning bolts are blueish-white and colossally bright. Interestingly, the physicist Planck derived that emission spectrum from purely classical considerations of systems of harmonic oscillators. I'm afraid I don't recall the derivation, but it has the curious property that it explains a fundamentally quantum mechanical phenomenon without the use of any quantum mechanics in the derivation. Purely classical! Planck's Constant h is found in the function that describes that spectrum, and can be calculated from that derivation. What is really cool is that Planck's Constant is also found throughout quantum mechanics. In QM h is almost always divided by 2 * PI, so to save writing we write an h with a diagonal slash through it, then drop the 2 * PI. This is pronounced "h bar". Now here is where it gets really bizarre: h bar divided by two is the spin of the electron! That is, when we say that electrons are spin one-half particles, we mean that their angular momentum is h bar divided by two. Spin one particles like photons have an angular momentum of one h bar. It took me a long, long, long time to come to grips with spin. Spin is angular momentum, and charged particles that have spin exhibit the magnetic fields that one would expect from rotating electric charges, but spin is NOT rotation. Spin is also quantized. If we subject an electron to a magnetic field, its magnetic pole will either line up with the applied field, or opposite to it. Only these two choices are permitted; nothing in between. Bound states of particles are individual particles themselves. They obey all the same laws as elementary particles, just in more complex ways. Thus rotation arises from systems of lots of particles that possess some kind of spin. A friend describes spin as "an irreparable tear in the fabric of the Universe". My Fedora case is black, but that's just because I wanted a case with ten drive bays, and the only ten bay case that Central Computers had in stock was black. That allows for a burner, a floppy, and (eventually) and eight-disk RAID. I only have four disks so far, but I'm planning for the future. It's been a long, long time, and I've forgotten all but the conceptual bits, but at one time I was an Astronomy major at the California Institute of Technology. Mike -- Don Quixote de la Mancha quixote@xxxxxxxxxxxxxxxx http://www.dulcineatech.com Dulcinea Technologies Corporation: Software of Elegance and Beauty. -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
