MODULE 3.1

Earth’s Energy Budget

Energy from the Sun and Earth

Lesson Goal:

» Contrast the amount and type of energy emitted by objects at different temperatures, in particular, the Sun versus Earth.

Energy from the Sun and Earth

What can we actually measure?

Taking the Sun’s temperature

T?

Reading Review

THE ELECTROMAGNETIC SPECTRUM

Gamma Ray X-Ray Ultraviolet Visible Infrared Microwave Radio

MO

DIF

IED

FRO

M H

TTP:

//M

YN

ASA

DAT

A.L

ARC

.NA

SA.G

OV/

IMA

GES

/EM

_SPE

CTR

UM

3-N

EW.JP

G

Which of these stoves is the hottest?

A B C

Which of these stoves is emitting radiation with the LONGEST peak wavelength?

A B C

They are all emitting at the same peak wavelength

D

Which of these stars is the hottest?

A B C

IMA

GE

CRE

DIT

S: N

ASA

Where are the peak wavelengths for the different stars?

THE ELECTROMAGNETIC SPECTRUM

Gamma Ray X-Ray Ultraviolet Visible Infrared Microwave Radio

MO

DIF

IED

FRO

M H

TTP:

//M

YN

ASA

DAT

A.L

ARC

.NA

SA.G

OV/

IMA

GES

/EM

_SPE

CTR

UM

3-N

EW.JP

G

Emission Spectra for Sun and EarthIM

AG

ES: N

ASA

Radi

atio

n In

tens

ity SUN

EARTH

0.1 1 10 100Wavelength, �(microns)

Infrared VIS UV

… Wien s law … Tsun = 5800 K ~0.5 +m

)&% )$%

Earth emits radiation with a peak wavelength of about 11.4 microns (µm).

A. ! 3.9 KelvinB. !15 KelvinC. ! 255 KelvinD. !273 KelvinE. 305 Kelvin

IMA

GE:

NA

SA

Using Wien’s Law, what’s Earth’s temperature?

Ȝm = 2897 / T

CHOOSE THE CLOSEST ANSWER.

Stefan-Boltzmann’s law (very useful!)

����������������� F is the energy emitted, per unit time, per unit area, expressed in W/m2 [J/s*m2]

is a constant [5.67*10-8 W/m2K4]

T is the absolute temperature (K)

64 million W/m2240 W/m2

IMA

GES

: NA

SA

Key Points

» The Sun gives off shortwave radiation with a peak wavelength in the visible part of the electromagnetic spectrum.

» The Earth gives off long wave radiation with a peak wavelength in the infrared part of the electromagnetic spectrum.

» The general relationships are that xHOTTER objects emit MORE radiation than cooler objects, and xHOTTER objects emit radiation at SHORTER wavelengths than cooler objects

» COMING UP: These differences between radiation from the Sun and radiation from Earth are crucial to understanding the greenhouse effect.