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The term emissivity is generally used to describe a simple, homogeneous surface such as silver. Similar terms, emittance and thermal emittance, are used to describe thermal radiation measurements on complex surfaces such as insulation products. [23] [24] [25]
Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only a temporary mitigation benefit. [53] [54] [55] [56]
The Bond albedo is a value strictly between 0 and 1, as it includes all possible scattered light (but not radiation from the body itself). This is in contrast to other definitions of albedo such as the geometric albedo, which can be above 1. In general, though, the Bond albedo may be greater or smaller than the geometric albedo, depending on ...
In slightly different terms, the emissive power of an arbitrary opaque body of fixed size and shape at a definite temperature can be described by a dimensionless ratio, sometimes called the emissivity: the ratio of the emissive power of the body to the emissive power of a black body of the same size and shape at the same fixed temperature. With ...
The effect of albedo on temperature can be approximated by assuming that the energy absorbed is multiplied by 0.7, but that the planet still radiates as a black body (the latter by definition of effective temperature, which is what we are calculating).
The effective temperature of the Sun (5778 kelvins) is the temperature a black body of the same size must have to yield the same total emissive power.. The effective temperature of a star is the temperature of a black body with the same luminosity per surface area (F Bol) as the star and is defined according to the Stefan–Boltzmann law F Bol = σT eff 4.
is Earth's average albedo, measured to be 0.3. [11] [12] is Earth's average surface temperature, measured as about 288 K as of year 2020 [13] is the effective emissivity of Earth's combined surface and atmosphere (including clouds). It is a quantity between 0 and 1 that is calculated from the equilibrium to be about 0.61.
Since the emissivity is limited by 1, the brightness temperature is a lower bound of the object’s actual temperature. For radiation emitted by a non-thermal source such as a pulsar, synchrotron, maser, or a laser, the brightness temperature may be far higher than the actual temperature of the source. [ 7 ]