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Definition: Radiant energy emitted by all
matter whose temperature is greater than
absolute zero (0° K).
Best known as VISIBLE LIGHT but includes
radio waves and ultraviolet waves too.
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The terms light, radiation, and
electromagnetic wave can all be
used to explain the same
concept.
Light comes in many forms.
 x-rays, visible light, radio
waves, etc. are all the
same phenomena
By using these different
wavelengths, astronomers
are able to gain a lot of
information on various
objects
Jupiter seen at different wavelengths of light
tells you different things.
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Electromagnetic Radiation can travel through
empty space (without a medium).
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They travel as vibrations in electrical and magnetic
fields
All forms of EM radiation travel at the SAME
SPEED.
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Speed of Light = 300,000 Km/sec
 Speed of Sound = 340 m/sec (.340 km/sec)
Click here Animation: Interaction of
vibrating charges
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One way to think about
light is as a traveling wave
A wave is just a disturbance
in some medium (water, air,
space)
A wave travels through a
medium but does not
transport material
A wave can carry both
energy and information
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Wavelength - distance between two like points on the wave
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Amplitude - the height of the wave compared to undisturbed state
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Period - the amount of time required for one wavelength to pass
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Frequency - the number of waves passing in a given amount of time
Electromagnetic Spectrum—name for the range of
electromagnetic waves when placed in order of increasing
frequency
• Click here (Animation—Size of EMwaves)
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Human eyes see the
visible part of the
spectrum
Longer wavelengths
includes infrared light,
microwaves, and radio
Shorter wavelengths
includes ultraviolet light,
X-rays, and gamma rays
All of these are forms of
electromagnetic
radiation
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A. Have the longest wavelengths and lowest
frequencies of all the electromagnetic waves.
B. A radio picks up radio waves through an
antenna and converts it to sound waves.
C. Each radio station in an area broadcasts at a
different frequency. # on radio dial tells
frequency.
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MRI (MAGNETIC RESONACE IMAGING)
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Uses Short wave radio waves with a magnet to
create an image
FM=Frequency modulation—waves
travel in a straight line & through
the ionosphere--lose reception when
you travel out of range.
AM=Amplitude modulation—
waves bounce off ionosphere can
pick up stations from different
cities.
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Microwaves—have the shortest wavelengths and
the highest frequency of the radio waves.
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Used in microwave ovens.
 Waves transfer energy to the water in the food causing them
to vibrate which in turn transfers energy in the form of heat
to the food.
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Used by cell phones and pagers.
RADAR (Radio Detection and Ranging)
 Used to find the speed of an object by sending out radio
waves and measuring the time it takes them to return.
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Infrared= LONGER than the color red
Shorter wavelength and higher frequency than
microwaves.
You can feel the longest ones as warmth on your
skin
Heat lamps give off infrared waves.
Warm objects give off more heat energy than cool
objects.
Thermogram—a picture that shows regions of
different temperatures in the body.
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What we see as white light is
actually made up of a
continuum of components
We break white light into
red, orange, yellow, green,
blue, indigo, and violet
(ROY G BIV)
 Red is the LONGEST
 Violet is the SHORTEST
Visible light is the Smallest
section of the EM Spectrum
• Referred to as UV rays
• Shorter wavelength and higher frequency than visible
light
• Carry more energy than visible light
• Used to kill bacteria. (Sterilization of equipment)
• Causes your skin to produce vitamin D (good for teeth
and bones)
• Used to treat jaundice ( in some new born babies.
• Too much can cause skin cancer.
• Use sun block to protect against (UV rays)
• Shorter wavelength and higher frequency than UVrays
• Carry a great amount of energy
• Can penetrate most matter.
• Bones and teeth absorb x-rays. (The light part of
an x-ray image indicates a place where the x-ray
was absorbed)
• Too much exposure can cause cancer
– (lead vest at dentist protects organs from unnecessary
exposure)
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Shorter wavelength and higher frequency than
X-rays
Carry the greatest amount of energy and
penetrate the most.
Used in radiation treatment to kill cancer cells.
Can be very harmful if not used correctly.
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If we could only observe in visible light, our
knowledge of the universe would be greatly
limited
By looking at objects at different wavelengths, we
get a different view and lots more information
Some objects are only visible at certain
wavelengths
Visible
Ultraviolet
X-ray
X-ray
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Invented by Dutch lens maker in 1608
Galileo: designed small 30X scope
Observed the moon and “began” the modern age of
Astronomy where measurement was more
important than philosophy
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Refracting (objective is a glass lens)
Reflecting (objective is a mirror)
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Newtonian
Cassegrain
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Earth’s atmosphere reflects certain
wavelengths
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Earth’s atmosphere blurs images
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x-rays, gamma rays and most UV light is not
transmitted by our atmosphere
the bending of light by the atmosphere depends
on the temperature of the “air”
“twinkling of stars” (Caused by movement of air)
“Light pollution”
Solution? Put the telescope in space.
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Can collect EM wavelengths that do not
penetrate the Earth’s atmosphere
Gamma rays
 X-rays
 Most Ultraviolet waves
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Can collect all EM radiation without disruption
from Earth’s atmosphere
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Images MUCH sharper
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Expensive to launch and maintain
Difficult to repair
Short lifetime
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Launched in 1990
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15 yr life expectancy
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Mirror error fixed ‘93
Going on year 20!!
96 minutes for 1 orbit
around Earth