The document discusses Earth's orientation in space and how its axial tilt, precession, and elliptical orbit affect seasonal changes in insolation levels. It explains that Earth's axial tilt varies between 21.5-24.5 degrees over tens of thousands of years, causing variations in seasonal temperatures. The tilt creates solstices when the sun is directly overhead at one of the Tropics, and equinoxes when it is overhead at the equator. Regions receive different levels of solar radiation depending on latitude and season, with implications for Earth's global heat balance.

1. Physical Geography
Lecture 3--Part 1
EARTH’S ENERGY and SEASONS

2. Earth in SpaceEarth in Space
 The Plane of theThe Plane of the
EclipticEcliptic

3. The Plane of the EclipticThe Plane of the Ecliptic

4. Variations in Earth’sVariations in Earth’s
MotionMotion
 Changes to Earth’s declinationChanges to Earth’s declination
 axial tilt (declination) varies fromaxial tilt (declination) varies from
2121°°59’ to 2459’ to 24°°36’ over the course36’ over the course
of about 40,000 yearsof about 40,000 years
 (it’s currently 23°26'28")(it’s currently 23°26'28")
 PrecessionPrecession
 this off-centered wobble changesthis off-centered wobble changes
shape over the course of aboutshape over the course of about
26,000 years26,000 years
 Orbital variationsOrbital variations
 Earth’s orbit changes fromEarth’s orbit changes from
elliptical to circular and back overelliptical to circular and back over
the course of about 93,000 yearsthe course of about 93,000 years

5. Earth’s OrbitEarth’s Orbit

6. Some Important PointsSome Important Points
(and Lines) to Remember…(and Lines) to Remember…

8. Why Earth’s Axial Tilt Is SoWhy Earth’s Axial Tilt Is So
ImportantImportant

9. Subsolar point
Sun’s rays are directly
overhead
Summer solstice
on or about June 22
Winter solstice
on or about December 22
Circle of Illumination
divides the day side and night
side of Earth
SolsticesSolstices

10. EquinoxesEquinoxes
Vernal (Spring) equinox
on or about March 22
Autumnal (Fall) equinox
on or about September 23

11. Electromagnetic Radiation
• All objects emit (radiate) EMR—waves that can
transport energy w/out requiring a medium
(matter) to pass through
• One of the most fundamental forms of energy in
our universe
• Given off as waves
• Different wavelengths have different properties

12. Shortwave vs. Longwave
Radiation
Electromagnetic radiation waves are measured in
micrometers (μm)

14. Two important principles of
electromagnetic radiation emissions:
1. There is an inverse relationship between the wavelength of
radiation an object emits and the temperature of that object
Long-wave = cool object
Short-wave = hot object
(Examples: iced tea vs. hot tea)
2. Hot objects radiate more energy than cool objects

15. What do you think?
Which one will emit MORE electromagnetic
radiation?
• The Sun
• Earth
Which one will emit mostly short-wave radiation?
• The Sun
• Earth

16. Insolation
Incoming Solar Radiation—EMR coming from our sun

17. Properties of Solar Radiation
Sol—Our star
• a ball of gases heated by constant nuclear reactions
• Surface temperature = 11,000°F (6000°C)
Radiation travels outward in all directions at a speed of 186,000
mps (300,000 kps)
• Takes 8 1/3 minutes to get to Earth (approx. 93 mil. miles away!)
• Reduction of wave energy as it spreads out
• Earth receives ½ of 1/billionth of the sun’s total energy

18. Properties of Solar Radiation
Most of the sun’s emissions
are in the form of short-wave
radiation
• high in the visible light
spectrum and short-wave
infrared
Visible light
• Wavelength of 0.4 to 0.7 μm
• Color is determined by
wavelength
• Even when there is enough
light to see shapes, can you
see colors in a darkened
room?

19. The Solar Constant
• Amount of radiation from the sun is nearly constant
• Atmospheric conditions and reflection cause a reduction of this
radiation within Earth’s atmosphere
• What we’re starting with is called the Solar Constant:
• The amount of solar energy received on a fixed surface area held
outside Earth’s atmosphere at right angles to suns rays.
• 1400 Watts/m2
• What happens to that insolation once it enters the atmosphere
will affect Earth’s energy budget (determining surpluses or
deficits) and, ultimately, our planet’s global heat balance

20. Insolation Levels
Different parts of Earth receive
different insolation levels
•The amount of insolation
received depends on two things:
• The angle of the sun’s
exposure
• The length of exposure
(length of the day)
•Both of these depend on:
• Latitude
• Season