A105 Stars and Galaxies

1
A105 Stars and Galaxies
Todays APOD
Rooftop _at_ 830 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
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
Examples A Sound Wave
speed wavelength x frequency

• Speed about 340 meters per second
• Frequency say, middle C (256-278 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

• 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

• 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
9
(No Transcript)
10
X-Rays and Gamma Rays

• X-rays and gamma rays absorbed in the Earths
  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 Sun
UV
X-Ray
Visible
Radio
Infrared
Composite
18
Venus Multiwavelength
UV
Visible
Infrared
Radio
19
A Mnemonic for the Electromagnetic Spectrum
GXUVIMR
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
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
• Temperature4
• 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
is

• Hotter thermal radiators are brighter at all
  wavelengths of light

HOTTER
BRIGHTER
29
Why dont 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
For Thursday...

• Finish units 21, 22, 23, 24, 25
• E.M. Radiation worksheet due
• Rooftop session at 830 Thurs.
• Kirkwood Open Night on Weds