The Electromagnetic Spectrum
Chapter 24, Section 1
What is the electromagnetic
spectrum?
The spectrum
arrangement of
electromagnetic
radiation ...
according to their
wavelengths and
frequencies.
Why is understanding light
important to astronomers?
Most of what we know about the universe is
the result of studying distant light sources.
The arrangement of
electromagnetic waves according
to wavelengths and frequencies is
called ...
the electromagnetic spectrum.
List the types of energies ...
FALSE
Different magnetic waves all travel the same
speed through a vacuum.
C = the speed of light
3.00 x 108 m/s2
Light ...
Sometimes behaves like waves.
Sometimes behaves like particles.
Called photons when it behaves like
particles.
Either/or. Never acts like both, at the same
time.
Getting wavelengths from light.
Light is made up of different wavelengths.
To separate, you will need a diffraction
surface.
Ex: Prism
Getting wavelengths from light.
Light is made up of different wavelengths.
To separate, you will need a diffraction
surface.
Ex: Diffraction Grating (aka Rainbow
Glasses)
Light as Particles
Called PHOTONS
Indicated with a
squiggly line
Wavelength
The distance from one wave crest (top of the
wave) to another
Measured in nanometers (nm)
1 nm = 10-9 m
Frequency
Frequency = how many wave crests (top of
the wave) will pass through a point in space
in one second (Hz)
The shorter the distance between crests, the
more that can pass through
How are Frequency and
Wavelength Related?
The shorter the ________, the higher the
____________.
How are Frequency and
Wavelength Related?
The shorter the ________, the higher the
____________.
X-rays and Gamma Rays
Are ultra-high-frequency electromagnetic
waves that can travel through matter, break
molecular bonds, and damage cells.
X-Rays are used to provide images of bones
and to examine suitcases at airports without
opening them.
Radiation therapy is used to kill diseased
cells.
Spectroscopy
Each light spectrum is unique to the material
producing it.
Can use spectrum as a “fingerprint” to figure
out what material it is.
Three types of spectra.
Continuous Spectrum
A solid object, when heated up, will produce
a continuous spectrum with all wavelengths.
Example: light bulb (the wire is a solid
object)
Continuous Spectrum
A solid object, when heated up, will produce
a continuous spectrum.
Example: metal
Continuous Spectrum
A solid object, when heated up, will produce
a continuous spectrum.
Example: rock (lava)
Blackbody Radiation
Every thing emits light all the time.
Normally, you don't notice because at
comfortable temperatures, most of the light
is infrared (invisible to the human eye).
At higher temperatures, objects start emitting
more visible light.
The higher the temperature, the more high
frequency light is emitted.
Absorption Spectrum
When a continuous spectrum passes through a gas.
The gas steals (absorbs) some of the wavelengths of
light.
The continuous spectrum now has gaps where those
wavelengths used to be.
Absorption Spectrum
Gaps tell you which gas the light went
through.
Absorption & Astronomy
Emission Spectrum
When a gas is heated, it will put off only
certain wavelengths of light.
Stars are spheres of hot gas.
Main Sequence Emission
Spectrum
Notice Anything?
What can a star's spectrum tell
astronomers?
Tells astronomers the chemical elements
present in the star.
Doppler Effect
When the source or the “listener” is in
motion it produces a distortion of
wavelength called the doppler effect.
http://www.youtube.com/watch?v=-t63xYSgmKE
http://www.youtube.com/watch?v=Man9ulEYSgk&feature=related
How is the Doppler effect used in
astronomy?
It helps determine if something is moving
toward or away from us.