Solar Spectrum
Bit of Administration ….
• c = 3 x 108 m/sec = 3 x 105 km/sec
• Reading
– BSNV pp. 153 - 168
The Physics of Light
• Doppler Shift
The Physics of Light
• Doppler Shift
• Source moving toward observer or
observer moving toward source
Shorter Wavelength
Higher Frequency
Blueshift
• Source moving away from observer or
observer moving away from source
Longer Wavelength
Lower Frequency
Redshift
The Physics of Light
• Doppler Shift
• Source across (perpendicular to) observer’s line of sight
Same Wavelength as emitted
Same Frequency as emitted
No Shift
Doppler Shift only provides measure of radial velocity,
or speed along the line of sight
The Physics of Light
• Doppler Shift

rest
vradial

c
vrad = radial velocity of light source or observer
(+=> away from each other)
 = change (shift) in wavelength = observed - rest
rest = rest wavelength
c
= 3 x 105 km/sec
ConcepTest!
When Mars is in the middle of its retrograde loop, you expect it to
show
A.
B.
C.
D.
A large redshift
No Doppler shift
A large blue shift
Depends on where it is in its orbit
The Physics of Light
• Light as a Particle = Photons
• Photon - A Discrete Unit of Light Energy
• Planck’s Law
E photon  h
c

 h
h = Planck’s Constant = 6.626 x 10-34 joule sec
 = wavelength in m, c = 3 x108 m/sec
The Physics of Light
• Light as a Particle = Photons
• Planck’s Law
Small wavelength
Large frequency
Large energy
Large wavelength
Small frequency
Small energy
The Physics of Light
• Spectroscopy and Atomic Physics
• Types of Spectra
Continuous - No spectral lines
Absorption - Dark lines superimposed on continuous spectrum
Emission - Isolated bright lines
The Physics of Light
•
Spectroscopy and Atomic Physics
•
Kirchoff’s Laws
1. An opaque object emits a continuous spectrum.
2. An opaque object viewed through a cooler gas will
produce an absorption spectrum.
3. A gas viewed against an empty background produces an
emission spectrum
The Physics of Light
• Spectroscopy and Atomic Physics
• Kirchoff’s Laws
The Physics of Light
• Spectroscopy
• Temperature - a measure of the speeds of particles
Room Temperature
300 oK
The Physics of Light
• Spectroscopy
• Thermal Radiation - Any opaque object that has a
temperature above 0 oK emits light
The Physics of Light
• Spectroscopy
• Thermal Radiation
The Physics of Light
• Spectroscopy
• Thermal Radiation
The Physics of Light
• Spectroscopy
• Thermal Radiation
• Wien Law
max
max

3x10

T
max in nm
T in oK
6
• Spectroscopy
The Physics of Light
• Thermal Radiation
• Wien Law
• Stefan-Boltzmann Law
Eflux energy emitted from square meter in one second
E flux  T
4
Stefan-Boltzmann constant

The Physics of Light
• Spectroscopy and Atomic Physics
• Kirchoff’s Laws
The Physics of Light
• Spectroscopy and Atomic Physics
• Quantum Mechanics - Electron can only be in certain specific
orbits <=> can only have certain specific energies
e
Quantum
Numbers
Hydrogen
Atom
The Physics of Light
• Spectroscopy and Atomic Physics
• Quantum Mechanics - Electron energy changes can only have
certain values corresponding to energy changes between orbits
==> only certain energies of photons can be absorbed or emitted
The Physics of Light
• Spectroscopy and Atomic Physics
White light
Photons/sec
• Shine “white” light onto hydrogen atom
Wavelength
The Physics of Light
• Spectroscopy and Atomic Physics
Photons/sec
• Only photons with energy equal to energy difference
between orbits 2 and 3 are absorbed. This energy
corresponds to a wavelength of 660 nm.
660 nm
Wavelength
The Physics of Light
• Spectroscopy and Atomic Physics
Photons/sec
• Photons with energy equal to energy difference
between orbits 2 and 3 are emitted. These photons
are emitted in all directions.
660 nm
Wavelength
The Physics of Light
• Spectroscopy and Atomic Physics
• Kirchoff’s Laws
The Physics of Light
• Spectroscopy and Atomic Physics
• Energy Level Diagrams
Ground State