(1) Where P (watts) is the radiated power from a body of area A (m2) at temperature T (K). Îµ is emissivity, a dimensionless number between 0 and 1 that determines the. efficiency of a body to radiate and absorb energy. A perfect radiator and absorber has an emissivity of 1. Soil, ice, rock, asphalt and human skin have emissivities slightly less than 1. Ï -8is the Stefan-Boltzmann constant, 5.67 x10 Wm-2T-4 T is the body temperature in Kelvin. So if absolute temperature (in Kelvin degrees) doubles, radiated power increases by a factor of sixteen. Also, changes in temperature alter radiation peak wavelengths. Temperature increases move peak radiation to smaller wavelengths and vice-versa. Equilibrium and Solid Angles
Martin Luther King was often seen wearing a gold Rolex DayDate at many of his speaking functions. Musician John Mayer is seen here wearing his Rolex Daytona. Talk show host Ellen DeGeneres also wears a Rolex Daytona. Actor Brad Pitt is often seen wearing a Rolex Explorer.
President John F. Kennedy wore many fine Swiss watches. A Yellow Gold Omega Ultra Thin, which he wore when he took the oath of office, was included in his collection, as well as this Yellow Gold Cartier Tank, which he was wearing in his family portrait and on the day he was assassinated.