Intro to Astronomical Spectroscopy: Solar Spectrum
Newton (1672): Split Light with Prism
Intro to Astronomical Spectroscopy: Solar Spectrum
Fraunhofer (1787-1826) - Dark lines at discrete λ
Intro to Astronomical Spectroscopy: Kirchhoff’s Laws
Bunsen & Kirchhoff (1860) - Laboratory experiments
3 Types of Spectra
Continuous (BB)
Emission (Hot Gas)
Absorption (Cool Gas)
Kirchoff’s Laws: 3 Types of Spectra in Astronomy
1. Continuous
3. Absorption
2. Emission
Kirchoff’s First Law
Hot, dense objects will produce a
continuous spectrum.
Examples - BLACKBODIES
Light Bulb Filament
(Hot Solid)
Interior of Sun
(Hot, dense gas)
Kirchoff’s Second Law
Hot, low density gases will produce an emission
spectrum.
Examples:
Star-Forming Nebula
(Hot, low density gas)
Neon Sign
(Hot, low density gas)
Emission in Orion
Kirchoff’s Third Law
Cool gases in front of a continuous source
produce an absorption spectrum.
Examples:
-Starlight viewed through
cold interstellar gas
-Outer layers of Sun
(cooler gas in front
of hot core )
Emission (and Absorption) in Orion
Intro to Astronomical Spectroscopy: Solar Spectrum
Fraunhofer (1787-1826) - Dark lines at discrete λ
Intro to Astronomical Spectroscopy: Kirchhoff’s Laws
Bunsen & Kirchhoff (1860) - Laboratory experiments
Each element/molecule has a spectral fingerprint!
3 Types of Spectra
Continuous (BB)
Emission (Hot Gas)
Absorption (Cool Gas)
Wavelength different for different Elements - WHY????
Intro to Astronomical Spectroscopy: Solar Spectrum
Continuous
Spectrum
(all wavelengths)
why?
Wedgewood (1792):
All ovens became “red hot” at the same T.
Bottom Line: All objects with T above absolute zero
emit and absorb light at all λ (with varying efficiency)
A Blackbody is a theoretical object that absorbs all
radiation incident on it & re-radiates it in the form of a
continuous spectrum across all λ
•Blackbodies have a characteristic spectrum
•Blackbodies are theoretical but can be closely
approximated by any object in thermodynamic
equilibrium
•Blackbodies have a characteristic spectrum
•Blackbodies are theoretical but can be closely
approximated by any object in thermodynamic
equilibrium
Intro to Blackbody Radiation: Kirchoff & Planck
Bunsen & Kirchhoff (1860) - Laboratory experiments
“How does the intensity of the electromagnetic radiation
emitted by a black body depend on the frequency of the
radiation and the temperature of the body?"
Answer: Wien, Rayleigh, Jeans & Planck
Intro to Astronomical Spectroscopy: Solar Spectrum
Continuous
Spectrum
(all wavelengths)
why?
Planck Function
Sun behaves as BB
»» Energies are
thermalized
(all possible states)
(but look closer...)
Spectral lines are produced by....
Emission/Absorption Spectrum of Hydrogen:
H-Alpha Emission