Solar Radiation//Christopherson, Chp.2
Goals to learn this lecture:
-What is electromagnetic radiation?
-What are the patterns of receipt of solar radiation on Earth?
-What are seasons and why do we have them?
Why it’s important: solar radiation drives physical systems and the biosphere
abbreviations used in document: ‘sorad’ = solar radiation; ‘bill.’ = ‘billion’; ‘amnt’ =
‘amount. Others should be self-explanatory I hope.
Earth-Sun relationships are critical to how Earth systems behave
-Revolution and Rotation = 2 very distinct characteristic of Earth
>Revolution: Earth orbits annually around sun in an ellipse (1 complete revolution/year)
>Rotation: Earth rotates eastwards daily on own axis, which gives day and night
aphelion and perihelion: related to certain distances of Earth from Sun at diff. times
aphelion. = July 4 /Summer: Earth at its farthest from Sun at this point in revolution
perihelion. = January 3 /Winter: Earth at its closest to Sun at this point in revolution
>Aphelion and perihelion raise questions against misconceptions about proximity to
Sun equitable with seasonality, since further we are, it’s summer, whereas closer we
are, it’s winter.
-typical of one of several 100 bill. stars in Milky Way Galaxy
-6000K @ surface
-Enormous mass @ high temp. & pressure nuclear fusion
-Sun emits charged particles which give phenomena such as solar wind, short-wave
>emits , at surface, high energy radiation travelling at speed of light
-energy transmitted as waves of electric and magnetic oscillations
-ELECTROMAGNETIC RADIATION is emitted by all matter with a temp. above absolute 0/
-radiation intensity emitted depends on the temp. of the object: Stefan-Boltzmann law
Q proportional to T^4
-Wavelength of radiation inversely related to surface temp (hotter = shorter
>wavelength is distance ‘twixt two adjacent peaks.
Why human beings don’t glow...
-comfy human skin temp ~ 33Cs
-Avg. Human surface area ~ 1.8m^2
-895 watts emitted (1 watt = 1 joule/s)PWR = energy emitted per unit time. Watt= unit
-This is similar to 9 household light bulbs
-Radiation is in the thermal infrared part of the spectrum (heat) not visib