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Physical Geography
Lecture 3--Part 1EARTH’S ENERGY and SEASONS
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Earth in SpaceEarth in Space
The Plane of the The Plane of the EclipticEcliptic
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The Plane of the EclipticThe Plane of the Ecliptic
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Variations in Earth’s Variations in Earth’s MotionMotion
Changes to Earth’s declinationChanges to Earth’s declination axial tilt (declination) varies from axial tilt (declination) varies from
212159’ to 2459’ to 2436’ over the course 36’ 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 changes this off-centered wobble changes shape over the course of about shape over the course of about 26,000 years26,000 years
Orbital variationsOrbital variations Earth’s orbit changes from Earth’s orbit changes from
elliptical to circular and back over elliptical to circular and back over the course of about 93,000 yearsthe course of about 93,000 years
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Earth’s OrbitEarth’s Orbit
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Some Important Points Some Important Points (and Lines) to Remember…(and Lines) to Remember…
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Why Earth’s Axial Tilt Is So Why Earth’s Axial Tilt Is So ImportantImportant
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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
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EquinoxeEquinoxess
Vernal (Spring) equinox
on or about March 22
Autumnal (Fall) equinox
on or about September 23
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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
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Shortwave vs. Longwave Radiation
Electromagnetic radiation waves are measured in micrometers (μm)
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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 objectLong-wave = cool objectShort-wave = hot object(Examples: iced tea vs. hot tea)
2. Hot objects radiate more energy than cool objects
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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
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InsolationIncoming Solar Radiation—EMR coming from our sun
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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
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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?
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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
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Insolation LevelsDifferent 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