from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The energy-emitting propensity of a surface, usually measured at a specific wavelength.
from the GNU version of the Collaborative International Dictionary of English
- n. Tendency to emission; comparative facility of emission, or rate at which emission takes place
from The Century Dictionary and Cyclopedia
- n. Emissive or radiating power.
- n. Specifically A physical constant by means of which the power of radiation of a body is quantitatively expressed.
Sorry, no etymologies found.
The amount of blackbody energy emitted is strictly and solely a function of the thermal temperature of the substance, mitigated by the characteristic of the substance called emissivity (which can, as you say, by frequency dependent).
Buy double-or triple-pane models, designated Energy Star with a "low E" (for "emissivity") coating.
Perhaps the most interesting realization is that the concept of reciprocity applies to the ‘kludge’ factor called emissivity – the correction value that permits a greybody to be modeled with planck’s law and stefan’s law – applies to the atmosphere.
Materials commonly used in urban areas for pavement and roofs, such as emissivity than the surrounding rural areas.
I used a black body approximation to the earth’s emissivity, that is, an emissivity of 1.
The roof is made of "low emissivity" or "cool" roof materials, so it reflects sunlight rather than absorbing its heat.
Builders can achieve significantly higher rates of energy efficiency with only a few minor changes: plugging air leaks in the building envelope so that the owner will not be heating or cooling the great outdoors; sealing the ducts that deliver heating and air conditioning with mastic glue instead of tape, which can disintegrate; installing better windows with a low-emissivity coating; and adding more insulation to basements, crawl spaces, walls and attics.
One of the largest manufacturers, Velux, offers triple-coated low-emissivity glass, which helps with energy efficiency.
In #3 you can omit discussion of emissivity and Stefan Boltzmann constants, and leave them out of the parenthetical term.
Finally, changes in the emissivity of the sun have taken place over billions of years, but there have been shorter-term variations that occurred over decades, centuries, and millennia.