1. The electromagnetic spectrum

2. The blackbody spectrum
BB formula
Applet

3. Visible (400 – 700 nm) is 43 % of total irradiance
(all called ‘short wave’)
Visible (400 – 700 nm) is 43 % of total irradiance
Note funny units
IR (> 700 nm) is 52% of total irradiance
UV = 5%
All EM radiation may also be considered to be made up of photons with energies (in eV):
Wavelength in meters

4. Latitude and longitude
Where is the latitude zero?
Where is the longitude zero?

5. Hour angle and solar noon
Solar noon: When the Sun lies in the meridian plane at your location
(when the Sun is most nearly overhead)
Hour angle ω: angle the Earth has rotated since the last solar noon
Earth rotates 15o per hour, so therefore
The “equation of time”
What’s that?

6. The “equation of time” – how much the “mean sun” is too slow see wikipedia for mathematical details
Mean Sun “late”
Mean Sun “early”

7. A really nice animation here
Earth’s orbit around the sun Earth’s spin axis is tilted with respect to normal to orbital plane
Vernal equinox 3/20-21
Summer solstice
(NH) 6/20-21
Winter solstice (NH) 12/21-22
Autumnal equinox 9/22-23
A really nice animation here

8. Apparent daily motion of the Sun
Days near the summer solstice (NH) – longest day
Days near the vernal & autumnal equinoxes
Days near the winter
solstice (NH) – shortest day

9. Apparent motion of Sun across the sky
Sun shown at solar noon on 3 special days of year
North star
Solar declination = angle between sun’s rays & the plane of the Earth’s equator. For the 3 dates shown, what is ?
What is her latitude?

10. Number of hours of daylight
Cool applet
Above what latitude does the sun never set?
When is the length of the day changing fastest?
At what latitude are the days & nights always 12 hrs long?

11. Example: How many hours of daylight are there in Fairfax on March 29
Example: How many hours of daylight are there in Fairfax on March 29? Our latitude: n = 89th day of year (leap year)
What is an easy check on this answer?

12. Monthly insolation versus time of year at 5 latitudes

13. What is assumed about collector orientation?
World insolation map
Germany is the leader in solar electricity capacity with 55% of the world total.
Which nation leads the world in solar electricity production? Is this the sunniest? x
Is the insolation symmetrical above & below the equator?
Why is the max insolation not at the equator?
Max insolation over deserts (not rain forests), where moisture tends to generate clouds

14. Better world map?

15. “window” in “window” out GHG’s Why the big difference? Width changes
with concentration
GHG’s
Infrared absorption from molecules with 3 or more atoms