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Solar radiation, the sun, etc

Course Code
Joseph Leydon

of 2
Geography Lecture #2
January 13, 2011
Solar Radiation
Earth rotates eastwards daily on its own axis (rotation)
Elongated/elliptical orbit around the sun
Aphelion- the point where the earth is furthest from the sun
Perihelion- point when the earth is closest to the sun
The Sun
6000 K surface
enough energy to fuse atoms together-> nuclear fusion
sun radiates energy at the speed of light in a spectrum
sun emits charged particles (solar wind)
What is radiation?
It is energy emitted as waves of electric and magnetic oscillations
Electromagnetic radiation is emitted by all matter with a temperature
Q (energy emitted from radiation) is proportional to the Temperature
of the object
Wavelength of radiation is inversely related to surface temperature
(hotter objects -> shorter wavelengths)
Comfortable human skin temperature = 33 degrees Celsius
Average human surface area ~ 1.8m2
895 watts emitted (1 watt= 1 joule per second)
similar to 9 household light bulbs
we give off emissions in the infrared part of the spectrum (heat)
absorption of different wavelengths by gasses in the atmosphere,
gamma and xrays get absorbed at 80 km from the earths surface
How much insolation does Earth intercept?
At the equator or anywhere where the sun is directly overhead is where
we receive the most radiation
Sub-solar point: where the sun is directly overhead ^
The same light energy diffused over a larger area reduces intensity
Averaged daily latitudinal energy imbalance (Net R) at the top of the
atmosphere -> spatial variation
Seasonal changes in insolation -> temporal variation
Changes in Suns position above the horizon and in day length
Declination= latitude of sub-solar point
Length of seasons
Difference between aphelion and perihelion not significant
Eccentricity: degree of departure from perfectly circular orbit
Varies from 0-1
Rotation and orbital position
Rotation- day length
Equator: day length = 12 hours year round
Axis is angled 23.5 degrees from the plane of the ecliptic
Axis always points to Polaris, no matter what time of year it is