The Amazing Power of Starlight By analyzing light received from a star astronomers learn about the stars Chemical composition Surface temperature Radius Total energy output Density ID: 691797
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Slide1
Atoms and SpectraSlide2
The Sun’s Visible-Light SpectrumSlide3
The Amazing Power of Starlight
By analyzing light
received from a star, astronomers
learn about the star’s
…
Chemical composition
Surface temperature
Radius
Total
energy outputDensityVelocity relative to EarthRotation periodMagnetic Fields
0Slide4
Continuous Spectrum
S
pectrum of a common (incandescent) light bulb spans all visible wavelengths, without breaksSlide5
Kirchhoff’s Laws of Radiation
A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths & produce a continuous spectrum.
0Slide6
Emission Line Spectrum
T
hin or low-density cloud of gas emits light only at specific wavelengths Depends on its composition & temperature,
Producing
a spectrum with bright emission lines.Slide7
Kirchhoff’s Laws of Radiation
2
. Low-density gas excited will emit light only at
specific wavelengths & produce emission spectrum.
Light excites electrons in atoms to higher energy states,
Which transition back to lower states,
emitting light at specific frequencies.
0Slide8
Emission Line Spectrum
LASER
LightAmplified
S
timulated
E
mission
R
adiationSlide9
Absorption Line Spectrum
A cloud of
gas between us & continuous source can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.Slide10
Kirchhoff’s Laws of Radiation
3
. Light with continuous spectrum passes through a cool, low-density gas, produces
absorption spectrum.
Light excites electrons in atoms to higher energy states,
The frequencies of light correspond to the transition energies absorbed from the continuous spectrum.
0Slide11
How does
light
tell us about matter?Slide12
What is matter?
Matter is protons, neutrons, & electrons
Most of mass in nucleus
Most of space in electron “cloud”Slide13
What is matter?
Slide14
Different Kinds of Atoms
Type of atom depends on # of protons
Most abundant:
Hydrogen (H)
1 proton, 1 electron
2nd:
Helium (He
)
2 protons, 2 neutrons, and2 electrons
0Slide15
Atomic Terminology
Atomic Number
= # of protons in nucleus Atomic Mass Number = # of protons + neutrons Slide16
Chemical Fingerprints
Each type of atom has a unique spectral fingerprint
.Why?Slide17
Chemical Fingerprints
Each type of atom has a unique spectral fingerprint
.Slide18
Electron Orbits
Electron orbits restricted to very specific radii and energies.
Electron energies different for each individual element.
r
1
, E
1
r
2
, E2
r
3
, E
3
0Slide19
Electron Orbits
Electron orbits restricted to very specific radii and energies.
Electron energies different for each individual element.
0
E
photon
= E
4
– E1
E
photon
= E
3
– E
1Slide20
Electron Orbits
Electron orbits restricted to very specific radii and energies.
Electron energies different for each individual element.
0
Wrong
energy isn‘t absorbed!Slide21
Chemical Fingerprints
Each type of atom has
unique electron energy levels.Each transition corresponds to a unique photon
energy & wavelength
.
Energy levels of hydrogenSlide22
Chemical Fingerprints
Downward
transitions produce a unique pattern of emission lines.Slide23
Chemical Fingerprints
Upward
transitions produce a pattern of absorption lines
… at
the same wavelengths.Slide24
Chemical Fingerprints
Observing the fingerprints in a spectrum tells us which kinds of atoms are present.Slide25
Example: Solar SpectrumSlide26
Three basic types of spectra
Continuous
Spectrum
Emission
Line Spectrum
Absorption
Line Spectrum
Spectra of astrophysical objects are usually combinations of these three basic types.Slide27
Thought Question
Which letter(s) labels absorption lines?
A
B
C
D
ESlide28
Thought Question
Which letter(s) labels absorption lines?
A
B
C
D
ESlide29
Thought Question
A
B
C
D
E
Which letter(s) labels the peak (greatest intensity) of infrared light?Slide30
A
B
C
D
E
Thought Question
Which letter(s) labels the peak (greatest intensity) of infrared light?Slide31
Thought Question
Which letter(s) labels emission lines?
A
B
C
D
ESlide32
Thought Question
Which letter(s) labels emission lines?
A
B
C
D
ESlide33
Color and Temperature
Orion
Betelgeuse
Rigel
Stars appear in different colors:
Blue
(like
Rigel
),
Y
ellow
(
like our
sun)
R
ed
(like Betelgeuse).
Colors
tell us about
star’s
temperature.
0Slide34
Color and Temperature
0
Read about Annie Cannon!Slide35
The Women of Harvard
0
Dava
Sobel
Author of “
Galileo’s Daughter
” Slide36
The Spectra of Stars
Inner, dense layers of a star produce a continuous (blackbody) spectrum.
Cooler surface layers absorb light at specific frequencies.
=> Spectra of stars are absorption spectra.
0Slide37
How does light tell us
the temperatures of planets and stars?
TWO Laws of Radiation!Hotter objects emit more light at all frequencies per unit area.
Hotter = much, Much, MUCH,
MUCH
brighter
Hotter objects emit photons with a higher average energy
.
Hotter = BLUERSlide38Slide39
How does light tell us the temperatures of planets and stars?Slide40
How does light tell us about
the motions of planets & stars?
DOPPLER effectMotion AWAY “stretches” wavelengths
Sounds are lower; light is redder
Motion TOWARD “compresses” wavelengths
Sounds are higher; light is bluerSlide41
Measuring the Shift
StationarySlide42
Measuring the Shift
Stationary
Moving AwaySlide43
Measuring the Shift
Stationary
Moving Away
Away FasterSlide44
Measuring the Shift
Moving Toward
Toward Faster
StationarySlide45
Doppler shift tells us ONLY about part of an object
'
s motion toward or away from us.Slide46
Doppler Shift Example:
Earth’s orbital motion around the Sun causes a radial velocity towards (or away from) any star.
0