Download RADIATION AND SPECTRA

RADIATION AND SPECTRA
Chapter 4
WAVES
 A stone
dropped into a pool of water causes an
expanding disturbance called a wave.
l
WAVES
 A stone
dropped into a pool of water causes an
expanding disturbance called a wave.

Sound is a wave caused by a pressure disturbance.

Light and radio are waves (called electromagnetic
radiation) caused by charged particles (mostly
electrons) oscillating.
PROPERTIES OF RADIATION
Speed = 3 x 105 km/s in vacuum.
 Radiation often behaves as a wave.
 Wavelengths (1nm = 10-9 m)
 Radio = 1m (109 nm)
 Infrared = 10 m (104 nm)
 Visible = 0.5  m (500 nm)
 Ultraviolet = 10 nm
 X-ray = 0.1 nm
 g-ray = 10-4 nm
 m = metre,  = 10-6, n = 10-9

ELECTROMAGNETIC RADIATION
not all reaches Earth’s surface
ELECTROMAGNETIC WAVES
some telescopes have to be in
space
HUMAN SENSITIVITY to WAVES

Sound Waves
l (wavelength) = pitch
Short l = high pitch
Long l = low pitch

Light Waves
l (wavelength) = colour
Short l = bluer
Long l = redder
NANOMETER

Usual unit of l for light is nm
(nano-meter = 10-9 metres)
Blue light = 400 nm
Red light = 700 nm
NANOMETER

Usual unit of l for light is nm
(nano-meter = 10-9 metres)
Blue light = 400 nm
Red light = 700 nm
Prism splits white light into component colours
ELECTROMAGNETIC RADIATION
Type of
Radiation
Gamma rays
Wavelength
Range (nm)
Less than
0.01
Radiated by
Objects at this
Temperature
More than 108 K
Typical Sources
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
GAMMA RAY SOURCE
Black Hole
GAMMA RAY SOURCE
Pulsar
ELECTROMAGNETIC RADIATION
Type of
Radiation
Wavelength
Range (nm)
Radiated by
Objects at this
Temperature
Typical Sources
Gamma rays
Less than
0.01
More than 108 K
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
X rays
0.01 - 20
106 - 108 K
Gas in clusters of galaxies;
supernova remnants; solar corona
X-RAY SOURCE
Eta Carinae
X-RAY SOURCE
Brahe’s Supernova
1572
ELECTROMAGNETIC RADIATION
Type of
Radiation
Wavelength
Range (nm)
Radiated by
Objects at this
Temperature
Typical Sources
Gamma rays
Less than
0.01
More than 108 K
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
X rays
0.01 - 20
106 - 108 K
Gas in clusters of galaxies;
supernova remnants; solar corona
Ultraviolet
20-400
104 - 106 K
Supernova remnants; very hot stars
ULTRAVIOLET SOURCE
Supernova
Remnant
ULTRAVIOLET SOURCE
Crab Nebula
Supernova Remnant
ULTRAVIOLET SOURCE
Young Stars
ELECTROMAGNETIC RADIATION
Type of
Radiation
Wavelength
Range (nm)
Radiated by
Objects at this
Temperature
Typical Sources
Gamma rays
Less than
0.01
More than 108 K
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
X rays
0.01 - 20
106 - 108 K
Gas in clusters of galaxies;
supernova remnants; solar corona
Ultraviolet
20-400
104 - 106 K
Supernova remnants; very hot stars
Visible
400-700
103 - 104 K
Stars
VISIBLE RADIATION
VISIBLE LIGHT SOURCE
note various stellar colours
Sagittarius
Star Cloud
VISIBLE LIGHT SOURCE
NGC 6543
(Planetary Nebula)
VISIBLE LIGHT SOURCE
Ring Nebula
(Planetary Nebula)
ELECTROMAGNETIC RADIATION
Type of
Radiation
Wavelength
Range (nm)
Radiated by
Objects at this
Temperature
Typical Sources
Gamma rays
Less than
0.01
More than 108 K
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
X rays
0.01 - 20
106 - 108 K
Gas in clusters of galaxies;
supernova remnants; solar corona
Ultraviolet
20-400
104 - 106 K
Supernova remnants; very hot stars
Visible
400-700
103 - 104 K
Stars
Infrared
103 - 106
10 - 103 K
Cool clouds of dust and gas;
planets; satellites
INFRARED SOURCE
Betelgeuse - brightest star in Orion
INFRARED SOURCE
Mars
INFRARED SOURCE
IINFRARED SOURCE
Io
INFRARED SOURCE
Trifid
Nebula
IR Image
ELECTROMAGNETIC RADIATION
Type of
Radiation
Wavelength
Range (nm)
Radiated by
Objects at this
Temperature
Typical Sources
Gamma rays
Less than
0.01
More than 108 K
Few astronomical sources this hot.
Some supernovae, pulsars, black
holes and gamma ray quasars.
X rays
0.01 - 20
106 - 108 K
Gas in clusters of galaxies;
supernova remnants; solar corona
Ultraviolet
20-400
104 - 106 K
Supernova remnants; very hot stars
Visible
400-700
103 - 104 K
Stars
Infrared
103 - 106
10 - 103 K
Cool clouds of dust and gas;
planets; satellites
Radio
More than 106
Less than 10K
No astronomical objects this cold.
Radio emission produced by
electrons moving in magnetic fields
(synchrotron radiation)
RADIO SOURCE
Antennae
Galaxies
RADIO SOURCE
Milky Way Galaxy
WINDOWS to the UNIVERSE
Many astronomical objects can be observed over a
broad band of wavelengths.

Radio
Infrared Visible Ultraviolet X-Ray Gamma Ray
BROAD BAND SOURCE
Radio
Optical
Infrared
Milky Way Galaxy Centre
BROAD BAND SOURCE
X-ray
Ultraviolet
Radio
Optical
The Sun
BROAD BAND SOURCE
X-ray
Optical
Infrared
Radio
Crab Nebula
BROAD BAND SOURCE
Centaurus A
BROAD BAND SOURCE
X-ray
Optical
Infrared
Radio
Coma Cluster
PROPERTIES OF RADIATION
Speed = 3 x 105 km/s in vacuum.
 Radiation often behaves as a wave.
 Wavelengths (1nm = 10-9 m)
 Radio = 1m (109 nm)
 Infrared = 10 m (104 nm)
 Visible = 0.5  m (500 nm)
 Ultraviolet = 10 nm
 X-ray = 0.1 nm
 g-ray
 m = metre,  = 10-6, n = 10-9
 Propagation of radiation

PROPAGATION of RADIATION
INVERSE SQUARE LAW (Intensity  R-2)
PROPERTIES OF RADIATION
Speed = 3 x 105 km/s in vacuum.
 Radiation often behaves as a wave.
 Wavelengths (1nm = 10-9 m)
 Radio = 1m (109 nm)
 Infrared = 10 m (104 nm)
 Visible = 0.5  m (500 nm)
 Ultraviolet = 10 nm
 X-ray = 0.1 nm
 g-ray
 m = metre,  = 10-6, n = 10-9
 Propagation of radiation
 Spectrum of radiation (blackbody)

WHITE LIGHT SPECTRUM
BLACKBODY RADIATION

Astronomical objects emit energy at different
wavelengths
ORION CONSTELLATION
Betelguese
Rigel
BLACKBODY RADIATION

Astronomical objects emit energy at different
wavelengths



WHY?
Temperature
Blackbody




- a source that absorbs all radiation hitting it.
Energy is then re-emitted at all wavelengths.
At higher temperatures, more energy is emitted.
 Energy emitted = T4
The higher the temperature, the shorter is the
maximum wavelength.
 lmax(nm) = 2.9 x 106 /T(ºK)
 ºK = ºC + 273
BLACKBODY CURVES
WIEN’S LAW
7,000 K
EMITTED ENERGY
(400 nm)
lmax
5,000 K
T = Temp ºK
lmax in nanometers
(580
nm)
x
4,000
 K

2.9x10 6

T
(725 nm)
3,000 K
(960 nm)
|
|
|
|
|
|
|
0
500
1000
1500
2000
2500
3000
WAVELENGTH (nm)
FLASHCARD
WHAT IS YOUR APPROXIMATE BODY
TEMPERATURE IN DEGREES K?
A) 100 K
B) 200 K
C) 300 K
D) 400 K
FLASHCARD
AT WHAT WAVELENGTH DO YOU PUT OUT
MOST OF YOUR ENERGY?
A) 100 nm (Ultra violet)
B) 1000 nm (deep red)
C) 10,000 nm (infrared)
D) 1,000,000 nm (short radio)
Interlude with special camera
DOPPLER SHIFT
Doppler Shift Formula
Change in wavelength = original wavelength x v/c
 c=300,000 km/sec
 eg wavelength 400 nm from source moving ½ c
away from you.

 change in wavelength = wavelength x v/c = 400 x ½
=200 nm
 wavelength thus observed at 600 nm

FLASHCARD
IMAGINE THAT YOU ARE ON A SPACESHIP,
SPEEDING TOWARDS MARS (THE RED
PLANET). YOU GET CONFUSED AND
MISIDENTIFY IT AS EARTH (THE BLUE PLANET).
HOW FAST WERE YOU GOING?
(c = 3 x 105 km’s, blue light = 400 nm, red light = 700 nm)
A) 2/7 c ( = 85,700 km/s)
B) 3/7 c (= 128,570 km/s)
C) 4/7 c (= 171,430 km/s)
D) 5/7 c (= 214,290 km/s)