ELECTROMAGNETIC SPECTRUM
Electromagnetic Radiation 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.
Light and the EM Spectrum 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.
Light and EM Radiation Electromagnetic Radiation can travel
through empty space (without a medium). They travel as vibrations in electrical and
magnetic fields All forms of EM radiation travel at the
SAME SPEED. Speed of Light = 300,000 Km/sec
Speed of Sound = 340 m/sec (.340 km/sec)Click here Animation: Interaction of vibrating charges
Light as Waves 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
Wave Terminology Wavelength - distance between two like points on the wave Amplitude - the height of the wave compared to undisturbed
state Period - the amount of time required for one wavelength to
pass Frequency - the number of waves passing in a given amount
of time
Electromagnetic SpectrumElectromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency• Click here (Animation—Size of EMwaves)
The Electromagnetic Spectrum
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
RADIO WAVES 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.
MRI of the Brain MRI (MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a magnet to create an image
Radio WavesFM=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.
MICROWAVES Microwaves—have the shortest
wavelengths and the highest frequency of the radio waves. 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.
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.
INFRARED RAYS
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.
INFRARED RAYSThermogram—a picture that shows regions of different temperatures in the body.
Wavelengths of Light - Visible
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
ULTRAVIOLET RADIATION• 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)
XRAY RADIATION• Shorter wavelength and higher frequency than UV-
rays• 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)
GAMMA RADIATION 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.
EM Spectrum in Astronomy
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
The Sun at Different Wavelengths
Visible Ultraviolet
X-ray X-ray
TELESCOPES
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
General types of Telescopes
Refracting (objective is a glass lens) Reflecting (objective is a mirror)
Newtonian Cassegrain
Problems with Earth-based telescopes
Earth’s atmosphere reflects certain wavelengths x-rays, gamma rays and most UV light is
not transmitted by our atmosphere Earth’s atmosphere blurs images
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.
Advantages of Space Telescopes
Can collect EM wavelengths that do not penetrate the Earth’s atmosphere Gamma rays X-rays Most Ultraviolet waves
Can collect all EM radiation without disruption from Earth’s atmosphere Images MUCH sharper
Disadvantages of space-based telescopes
Expensive to launch and maintain
Difficult to repair Short lifetime
HUBBLE SPACE TELESCOPE
Launched in 1990 Mirror error fixed
‘93 15 yr life
expectancy Going on year 20!!
96 minutes for 1 orbit around Earth
HUBBLE IMAGES