1. Electromagnetic Spectrum

2. Warm-up
How would you define light?

3. Light and the Electromagnetic Spectrum
Almost all of our information on space is derived from the light we see
We have only returned samples from the Moon and a comet
Also obtained meteor samples
We have landed (with unmanned probes) on only a handful of planets and moons

4. Light and the EM Spectrum
The terms light, radiation, and electromagnetic wave can all be used to explain the same concept, they are synonymous
Light comes in many forms and it took physicists some time to realize that x-rays, visible light, radio waves, etc. are all the same phenomena
By using these different tools, astronomers are able to gain a lot of information on various objects
Jupiter seen at different wavelengths of light

5. Light as a Wave 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. Wavelengths of Light - Visible
What we see as white light is actually made up of a continuum of components
Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)
There is actually a continuous transition of color, each with its own wavelength and frequency

8. The Electromagnetic Spectrum
Human eyes are only able to process information from the visible part of the spectrum
Toward longer wavelengths, the spectrum includes infrared light, microwaves, and radio
Toward shorter wavelengths, the spectrum includes ultraviolet light, X-rays, and gamma rays
All of these are forms of electromagnetic radiation

9. Characteristics of Radio waves:
longest wavelength
shortest wavelength
Characteristics of Radio waves:
Longest wavelength.
Transmit radio and TV signals.

10. Characteristics of Microwaves:
longest wavelength
shortest wavelength
Characteristics of Microwaves:
Shorter than radio waves.
Absorbed by water molecules.

11. Characteristics of Infrared waves:
longest wavelength
shortest wavelength
Characteristics of Infrared waves:
Shorter wavelength than microwaves.
Felt as heat.
Hot objects give off infrared waves.

12. Characteristics of Visible light:
longest wavelength
shortest wavelength
Characteristics of Visible light:
Shorter wavelength than infrared waves.
Can be seen as colors.
Half of Sun’s rays are visible light.

13. Characteristics of Ultraviolet light:
longest wavelength
shortest wavelength
Characteristics of Ultraviolet light:
Shorter wavelength than visible light.
Give off harmful radiation.
Can kill living cells.
Causes skin cancer.

14. Characteristics of X-ray radiation:
longest wavelength
shortest wavelength
Characteristics of X-ray radiation:
Shorter wavelength than ultraviolet.
Give off harmful radiation.
Pass through skin, not bone.
Harmful to humans.

15. Characteristics of Gamma radiation:
longest wavelength
shortest wavelength
Characteristics of Gamma radiation:
Shortest wavelength (highest energy).
Comes from radioactivity or nuclear reactions.
Give off harmful radiation.
Harmful to humans.

16. Warm-up
Complete the worksheet you picked up on the way in (both sides)

17. 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

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

20. Measuring Temperature from Light
Astronomers can use the light from an object to measure its temperature
Astronomers also use a different unit for temperature, the Kelvin
Water boils at 373 K and freezes at 273 K
Most stars have a temperature in the 1000's of Kelvin
The coldest possible temperature (absolute zero) corresponds to 0 Kelvin

21. Measuring Movement from Light
The motion of an object can be measured through a change in the frequency of the waves emitted by the object called the Doppler effect
The increase in pitch of an approaching police car is caused by the compression of the sound wave
The pitch decreases as the police car moves away

22. Doppler Shift In astronomy, the same effect happens to light waves
A source that is moving away will appear redder (redshift)
A source that is moving toward us will appear bluer (blueshift)
Note: Only objects moving toward or away from us will show this effect

23. Mnemonic device Rotten Men Inevitably Visit Ugly X-Girlfriends
Rabbits Mate In Very Unusual eXpensive Gardens
Randy Men In Vegas Uses X-rays on Girls
Raging Martians Invaded Venus Using X-ray Guns