The Electromagnetic Spectrum
A Very Short Discussion of Waves.
Waves
Waves are pure energy.
Waves carry energy from place to place.
Examples of waves are
Heat
Sound
Light
Water
Characteristics of Waves
 All waves have
 Wavelength ( l )
 Amplitude
 Speed – how fast a crest travels from one place to another.
 Frequency – how many waves pass a point in a unit of time.
Electromagnetic Waves
The E-M spectrum contains waves that have
similar characteristics.
These waves do not require a medium and
travel at the speed of light. 186,000 miles per
hour
The Electromagnetic Spectrum
How is the Electromagnetic
Spectrum used in astronomy?
Radio Waves
Have the largest
wavelengths of all
light waves. They
can be up to several
kilometers long.
Used in Radios, TVs,
Communication, and
cell phones.
Radio Waves and Astronomy
Space objects emit light at many different
wavelengths.
Some of the wavelengths are in the radio
wave area of the EM spectrum.
Radio waves are collected by radio
telescopes and intrepreted.
Radio Telescopes
Parks Radio telescope
Very Large Array (VLA)
These radio telescopes reflect radio waves into a
single focal point where they are collected.
What do radio waves show us?
Different astronomical objects emit
different lengths of radio waves.
Scientists can study these emissions in
order to learn about the makeup and
structure of the universe.
CO gases in our milky way galaxy as seen by radio
waves
Microwaves
Have wavelengths
that can be measured
in centimeters
Used in
communication,
cooking food,
sensing, and
imaging.
RADAR
An acronym for “radio detection
and ranging”
Developed to determine an
objects position by firing bursts of
microwaves and recording their
echo.
Microwaves are able to penetrate
haze, clouds, and snow.
A radar image
from the Space
Shuttle.
Cosmic Microwave Background
The universe is constantly giving off
microwaves. This phenomenon has been
dubbed Cosmic Microwave background.
Cosmic Background Explorer (COBE) image
Infrared Radiation
Ranges in size from a single cell to the
head of a pin.
Used in imaging, heating food, and
remote controls.
Long infrared rays cab be felt as heat,
short ones cannot be detected by humans.
How do we see with infrared?
Any object that has a
temperature radiates
infrared radiation
(much in the same
way very hot objects
will emit visible
light)
Making Infrared Pictures
 A special camera is used
that is able to detect
temperature. Each
temperature is assigned
a different “false color.”
Generally, the warmer
an object, the more red
or orange it is. The
colder, the more blue.
This is an image of a cat
in infrared.
So why use it in Astronomy?
It is easy to study
cloud structure.
Dark clouds are
warmer than light
clouds.
We are able to study
the effects of
urbanization on the
earth.
What do the red areas
represent in this satellite
image?
Infrared images can tell us things about space
such as the concentration of stars and dust.
Image of the Milky Way. The hazy, horizontal Sshaped feature that crosses the image is faint heat
emitted by dust in the plane of the Solar System
Visible Light
The only
electromagnetic
waves we can see.
Their intensities
range from red to
violet with violet
being the highest in
energy.
True Color vs False Color
True color—an image that is the same as
our eyes would see it.
False color—computers record numbers
relating to brightness in another area of
the spectrum such as radio waves. The
computer then assigns values to these
intensities. It is much like color by
number!
True Color image of
Phoenix, AZ
False Color image
of Phoenix, AZ
The planet Uranus in False and
true color.
Ultra Violet Radiation
Used in tanning booths, sterilization
Responsible for sun burns and eye
cataracts
Ultra Violet Light and Astronomy
Hubble Space
telescope uses UV
light
Satellite image of the sun in
ultra violet light.
The hottest and most
active objects in the
universe give off UV
light. Scientists can
learn about these
objects by studying the
amount of UV light
given off.
False color image of the
earth using UV light.
Which side of the Earth
is facing the sun? How
do you know?
 Pictures like the one above show which galaxies are
new and which ones are old. The top row shows three
galaxies in UV light and in visible light in the bottom.
X-Rays
Used in x-ray photographs.
Extremely small wavelength. Extremely
high frequency and energy.
The earth’s atmosphere is thick enough
that x-rays are not able to penetrate to
the surface.
 When the Sun shines on
us at a certain angle, our
shadow is projected onto
the ground. Similarly,
when X-ray light shines
on us, it goes through
our skin, but allows
shadows of our bones to
be projected onto and
captured by film.
X-Rays in Astronomy
Astronomers are able to load x-ray
detection machines on to satellites.
These satellites are able to detect things
like the number of photons collected, the
energy of the photons collected, or how
fast the photons are detected, can tell us
things about the object that is emitting
them.
Many things in space
emit X-rays, among
them are black holes,
neutron stars, binary
star systems,
supernova remnants,
stars, the Sun, and
even some comets!
http://chandra.harvard.edu/
The sun in x-ray
Gamma Rays
Have the smallest wavelength, highest
frequency, and highest energy of any other type
of electromagnetic radiation.
Generated by radioactive atoms in nuclear
explosions.
Produced in the hottest regions of the universe
Things like supernova explosions (the way
massive stars die), neutron stars and pulsars,
and black holes are all sources of celestial
gamma-rays.
Gamma rays give us information
into such things as nebulas.