The Sun: Facts of Interest
Origin of the Universe:
- The Big Bang.
- Things cool, Gravitational Attraction,
- Forms Stars. Gravitational Potential Energy goes to heat.
- Lots of hydrogen around. Hydrogen undergoes Fusion Process,
Basically
E is Heat. The Heat comes from the missing mass. Mass is
Energy
Physical Properties of the Sun
- 1.39 million km in diameter
- 150 million kilometers from the earth
- Interior Temp 2x10^7K
- Photosphere Temperature 5800K
Electromagnetic Waves (Radiation)
- Physics
2000 Tutorial on Electromagnetic Waves
- Caused by moving charges
- Propagates as waves ( Sort of Like Water Waves on a pond)
- Waves have a physical length (Wavelength measured in meters.
Mathematical Symbol l)
- Waves have a repeated motion ( Frequency, Cycles per second,
Hertz, Abbreviated Hz Mathematical Symbol f)
- Travel with Velocity ( Product of wavelength x Frequency v
= l f)
- Color of Visible Light Depends on Wavelength
Blackbody Radiation Expanded
- Wavelength Emitted Depends On Temperature
- The Hotter, the More Shorter the Wavelengths
- l = Constant /
Temperature
- Recall E = sT4 (
s = 5.67 * 10-12
w/cm2-K4)
Solar Terms
- Insolation: Incident Solar Radiatio: In the U.S. average betwees 12,000-22,000kJ/m2/d
- Albedo: The fraction of light reflected from the earth and atmosphere.
- Greenhouse Effect: The reradiation of energy back to the Earth.
- Solar Constant: The insolation that reaches the top of the Earth, = 1360W/m2.
- Insolation changes at different seasons due to the tilt of the Earth. In Winter, more radiation is absorbed and scattered by the atmosphere.
- Altitude: The sun's elevation above the horizontal. This changes with latitude and the seasons.
- Solar Azimuth: The angle of the sun from true south.
Types of Solar Radiation
- Direct. The direct sunrays striking a surface.
- Diffuse The light that is scattered from the sky
- Reflected Radiation from the ground, surrounding buildings,etc.
Demos on Absorption, Reflection and Refraction.
- Different materials will be transparent at different
wavelengths.
- Example Glass is Opaque to UV And Infrared. Allows
Visible Through
- Some Objects may absorb some wavelengths well but reflect
other wavelengths.
- Example: Red Shirt absorbs other colors, but reflects
red.
- r %(reflected radiation) + a
%( absorbed radiation) + t
%(transmitted radiation) = 100% (The Total Radiation
Hitting the Surface.)
Solar Applications
Measuring Solar Radiation.
Amount of Insolation changes in the seasons because of the suns angle and atmosphere absortion. Checkout Understanding Seasonal and Atmospheric Variations
Sunset Demo: Scattered light/. Why is the sky blue??
Measuring Devices
Incident Solar Radiation
Renewable Resource Data
Center Info on Solar Data Shining
On
Accurate information is important for designing
energy systems.
Solar radiation data provide information on how
much of the sun's energy strikes a surface at a location on earth
during a particular time period.
Values of energy per unit of area. Shows
naturally occurring changes in the amount of solar radiation over the
course of days, months, and years,
for a location.
Units of measurement are:
- kilowatt-hours per square meter (kWh/sq m)
- megajoules per square meter (MJ/sq
m),
- Langleys (L) a unit of heat energy equivalent to one calorie falling on one square centimeter of surface. One BTU per square foot is the equivalent of 0.27125 Langley.
- British thermal units per square foot
(Btu/sq ft).
National Solar Radiation Data Base.
- Covers 30 years (1961-1990)
- Information recorded by more accurate
instruments and better models.
- 1992, this new database available for 250
sites.
A Rap on The dependence on Angles and Solar
Radiation...With Demo...
Let's Go to Shining
On for more on measuring Solar
Radiation
