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ContinuousSpectra.ppt
Spectral Types – Continuous Spectra
A spectrum of electromagnetic waves that involves a wide range (continuous
range) of wavelengths.
In the visible portion of the electromagnetic spectrum, a continuous spectrum
would look like a rainbow
Spectral Types – Continuous Spectra
Kinetic Theory
The Temperature of an object is a measure of the kinetic energy of the
particles in the system.
The higher the kinetic energy of the particles, the higher the temperature.
Solids, liquids – Temperature primarily determined by vibrational kinetic energy
of the particles in the system
Gas – Temperature is determined by the translational kinetic energy of the
particles in the gas
Spectral Types – Continuous Spectra
Continuous emission of electromagnetic waves
When the particles in the solid, liquid, or gas accelerate, they will
produce EM waves.
Mechanisms:
Particle vibrations (solids, liquids)
Electron transitions in chemical bonds (solids, liquids)
Particle-particle collisions (gasses)
Spectral Types – Continuous Spectra
Stellar Spectra
EM waves emitted from a star result from the collisions of charged
particles within the star.
Particle in the star move with very high kinetic energies. Energy
changes occur as a result of particle - particle collisions.
Energy loss through collision
Spectral Types – Continuous Spectra
Stellar Spectra
Since a wide range of energies can be experienced by the particles, a
similarly wide range of frequencies of photons can be emitted.
However, the temperature of the star determines how much kinetic
energy is associated with the particle motion.
The hotter the star, the more energetic the collision. Therefore, the
higher the energies of the emitted photons.
Spectral Types – Continuous Spectra
Stellar Spectra
Since for a photon
E=hf
The energy carried by the photon determines the position of the
electromagnetic wave on in the electromagnetic spectrum.
If the resulting frequency is within the visible window, the energy of the
photon will determine the color of the electromagnetic wave.
Spectral Types – Continuous Spectra
Blackbody radiation
λPeak
Spectral Types – Continuous Spectra
Blackbody radiation
"Blackbody radiation"
refers to an object or
system which
absorbs all radiation
incident upon it and
re-radiates energy
which is
characteristic of this
radiating system only,
not dependent upon
the type of radiation
which is incident
upon it.
Spectral Types – Continuous Spectra
Stellar Spectra
Because of the wide range of photon energies available through
collisions of the particles in a star, a star will emit blackbody radiation.
Since the frequency of emitted photons will be determined by the
temperature of the star, there is a direct relationship between the color of
the star and it’s temperature.
Website to view a temperature adjustable blackbody radiation curve
Spectral Types – Continuous Spectra
Blackbody radiation
Physical Laws Governing BB radiation
Wien’s Law
Wavelength of Peak Emission =
0.29
Temperature in K
cm
Spectral Types – Continuous Spectra
Blackbody radiation
Physical Laws Governing BB radiation
Stefan’s Law
Power Emitted per unit Area = σ T4
σ = 5.67 x 10-8 W / m2 – K4
Note: A Watt (W) is a Joule/Sec
(Stefan-Boltzmann constant)