Solar And Terrestrial Radiation PDF

Solar and Terrestrial Radiation ABE 57 Lecture 1 The Sun ▪ A 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium ▪ Radius ~ 6.96 x 108 m ▪ Surface Temperature ~ 5780 K Radiation ▪ Energy that comes from a source and travels through space at the speed of light....

Solar and Terrestrial Radiation ABE 57 Lecture 1 The Sun ▪ A 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium ▪ Radius ~ 6.96 x 108 m ▪ Surface Temperature ~ 5780 K Radiation ▪ Energy that comes from a source and travels through space at the speed of light. Radiation ▪ Blackbody ▪ emits radiation at maximum possible intensity for every wavelength ▪ absorbs all radiation incident upon it ▪ perfect emitter; perfect absorber ▪ Emissivity (ξ) ▪ the ratio of the emittance of a surface or body to that of the emittance of a blackbody at a particular wavelength and temperature ▪ Hence, ξ blackbody = 1.0 Stefan-Boltzman Law ▪ “All bodies (no matter how big or small) with temperature above absolute zero emits radiation.” ▪ “The rate of emission is proportional to the 4th power of their absolute temperature.” 𝑬 = 𝝈𝑻𝟒 ▪ E = total amount of radiation emitted by an object per square meter (W/m2) ▪ σ = Stefan-Boltzman constant (5.67x10-8 W/m2-K4) ▪ T = temperature (K) Wien’s Displacement Law ▪ “The higher the object’s temperature, the shorter are the wavelengths of emitted radiation.” ▪ “As an object’s temperature increases, its peak emission of radiation shifts toward shorter wavelengths.” 𝟐𝟖𝟗𝟕 𝝁𝒎 − 𝑲 𝝀𝒎𝒂𝒙 = 𝑻 ▪ λmax = maximum wavelength (μm) ▪ T = temperature (K) Wien’s Displacement Law Solar Constant ▪ It is the radiant flux density (RFD) reaching the top of the earth’s atmosphere; on a surface perpendicular to the incident radiation; when earth is at its mean distance from the sun. Solar Constant