1. A105 Stars and Galaxies Today’s APOD Rooftop @ 8:30 PM on Thursday!
Homework 3 due Sept. 14
EM Radiation
Read units 21, 22, 23, 24, 25
News Quiz TODAY
Observing the Full Moon

2. Monitoring the Sun with SOHO
Last Thursday
Monitoring the Sun with SOHO
Sunday
Orbits between the Sun and Earth, about a million miles away – a constant view of the Sun
Today

3. LIGHT!
Applet: RGB

4. What does “electromagnetic” mean?

5. Wavelength and Frequency
Properties of waves
speed (distance per second)
wavelength (length)
frequency (cycles per second)
speed = wavelength x frequency

6. speed = wavelength x frequency
Examples – A Sound Wave
Speed – about 340 meters per second
Frequency – say, middle C ( cycles per second depending on the scale)
What is the wavelength?
340 m/sec = W x 278 per second

7. Example – A Tsunami Wave
speed = wavelength x frequency
Example – A Tsunami Wave
speed – about 700 km/hour (200 m/sec)
Wavelength – about 50 km
What is the frequency of the wave?
700 (km/hour) = 50 (km) x frequency
frequency = 700/50 = 15 cycles per hour

8. Examples – An Electromagnetic Wave
speed = wavelength x frequency
Examples – An Electromagnetic Wave
speed – 300,000 km per second (3 x 108 meters per second)
frequency – say, one billion cycles per second (109 cycles per second)
What is the wavelength?
What kind of light is this?
3 x 108 m/sec = W x 109 /sec

10. X-Rays and Gamma Rays
X-rays and gamma rays absorbed in the Earth’s atmosphere
Observatories must be sent into space
Produced by matter heated to millions of degrees
Caused by cosmic explosions, high speed collisions
Led to the discovery of black holes in space
Allow us to study the hottest regions of the Sun's atmosphere

11. Ultra-Violet Ultraviolet light is blocked by the ozone layer
Astronomers use balloons, rockets, and satellites
Most stars are too cool to emit much UV light
UV sources include very young stars, some very old stars, white dwarfs stars, active galaxies and quasars
Discoveries include a hot gaseous halo surrounding our own galaxy that glows in the UV

12. Visible Light
Ground-based observatories “see” during clear sky evenings
Adaptive optics eliminate the blurring effects of the atmosphere
In space we can get a much clearer view of the cosmos
Visible light observations give us the most detailed views of our solar system, and have brought us fantastic images of nebulae and galaxies
Stars are brightest in visible light

13. Infrared
Some bands of infrared light can be observed by ground-based observatories
To view the rest of the infrared universe we need to use space based observatories or high-flying aircraft
Infrared is primarily heat radiation
Infrared sees through thick regions of dust in space to peer into star-forming regions and into the central areas of our galaxy
Cool stars and cold interstellar clouds which are invisible in optical light are also observed in the infrared

14. Microwave Astronomy Wavelengths of about 1 mm to 1 m
The cosmic microwave background (electromagnetic radiation left over from the Big Bang) is now observed in the microwave part of the spectrum
Cold interstellar clouds are microwave sources
The early stages of star formation are observed in microwaves

15. Radio Radio waves are long compared to other EM waves
Most radio radiation reaches the ground and can be detected during the day as well as during the night
Radio telescopes use a large metal dish to collect radio waves
Radio telescopes first detected the radiation left over from the Big Bang
Supernovae, quasars, pulsars, regions of gas between the stars, and interstellar molecules radiate in the radio

16. Multiwavelength Orion
Optical
X-Ray UV
Radio
Infrared

17. The Multiwavelength SunUV
X-Ray
Visible
The Multiwavelength Sun
Radio
Infrared
Composite

18. Venus MultiwavelengthUV
Visible
Infrared
Radio

19. A Mnemonic for the Electromagnetic Spectrum…
GXUVIMR
A Mnemonic for the Electromagnetic Spectrum…
RMIVUXG
Really Messy Insane Valentine Unlike (ex) Girlfriend
Reindeer Make Interesting Visitors Uttering X-mas Greetings
Great X-rated (Unacceptable) Videos In My Room
Roy Marches In Very Unique X-ray Glasses
Randy Makes Interesting Voices Under Xtreme Gasses
Gamma Rays
X-rays
Ultraviolet
Visible
Infrared
Microwave
Radio

20. Exploring Color
Astronomy Rules!
Astronomy
is looking up!

21. Astronomy and Color

22. Astronomy and Color

23. Where does light come from?
THERMAL EMISSION
ATOMIC EMISSION
Thermal radiators emit light at all wavelengths
Atomic emission occurs only at particular wavelengths

24. All matter glows with light Even hotter matter glows blue hot
Cool matter glows
primarily with radio
or infrared light
All matter glows
with light
Warmer matter glows
with higher energy
light
Even hotter matter
glows blue hot
Matter at about
10,000 degrees centigrade
glows white hot

25. The glow of matter because of its temperature is called
Thermal Radiation
Thermal radiators emit light at all wavelengths
Cooler object peak at longer wavelengths (redder)
Hotter objects peak at shorter wavelengths (bluer)
The higher the temperature, the shorter
the peak wavelength
Very cool objects peat at radio wavelengths and very hot
objects peak at ultraviolet, x-ray, or gamma-ray wavelengths

26. Temperature Matters! The energy emitted directly proportional to
As stars get hotter, their energy output increases quickly!
A star 10 times hotter than Sun has 10x10x10x10 =10,000 times more energy output

27. We need to define TEMPERATURE!
Fahrenheit (used in the U.S.)
Centigrade/Celsius – based on the freezing and boiling points of water
water freezes at 0 C
water boils at 100 C
Kelvin temperature scale
0 K (-273 centigrade) is the coldest temperature possible (absolute zero)
water freezes at +273 K
water boils at +373 K
room temperature 300 K

28. 5000 K
3000 K
6000 K
7000 K
8000 K
4000 K
Hotter thermal radiators are brighter at all wavelengths of light
HOTTER is
BRIGHTER

29. Why don’t we glow in the dark?
People only reflect light.
People emit infrared light that is invisible to our eyes.
People are too small to emit enough light for us to see.
People do not contain enough radioactive material.

30. E.M. Radiation worksheet due Rooftop session at 8:30 Thurs.
For Thursday...
Finish units 21, 22, 23, 24, 25
E.M. Radiation worksheet due
Rooftop session at 8:30 Thurs.
Kirkwood Open Night on Weds