Physical Geography

Lecture 3--Part 1EARTH’S ENERGY and SEASONS

Earth in SpaceEarth in Space

The Plane of the The Plane of the EclipticEcliptic

The Plane of the EclipticThe Plane of the Ecliptic

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

Earth’s OrbitEarth’s Orbit

Some Important Points Some Important Points (and Lines) to Remember…(and Lines) to Remember…

Why Earth’s Axial Tilt Is So Why Earth’s Axial Tilt Is So ImportantImportant

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

EquinoxeEquinoxess

Vernal (Spring) equinox

on or about March 22

Autumnal (Fall) equinox

on or about September 23

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

Shortwave vs. Longwave Radiation

Electromagnetic radiation waves are measured in micrometers (μm)

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

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

InsolationIncoming Solar Radiation—EMR coming from our sun

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

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?

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

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