1. ELECTROMAGNETIC SPECTRUM

2. 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.

3. 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.

4. 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

5. 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

6. 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

7. Electromagnetic Spectrum
Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency
Click here (Animation—Size of EMwaves)

8. 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

9. 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.

10. MRI of the Brain MRI (MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a magnet to create an image

11. Radio Waves
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.

12. 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.

13. 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.

14. INFRARED RAYS
Thermogram—a picture that shows regions of different temperatures in the body.

15. 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

16. 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)

17. 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)

18. 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.

19. 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

21. The Sun at Different Wavelengths
Visible
Ultraviolet
X-ray
X-ray

22. 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

23. General types of Telescopes
Refracting (objective is a glass lens)
Reflecting (objective is a mirror)
Newtonian
Cassegrain

24. 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.

25. 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

26. Disadvantages of space-based telescopes
Expensive to launch and maintain
Difficult to repair
Short lifetime

27. 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

28. HUBBLE IMAGES