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Spectroscopy
The study of light emissions and
absorptions
The Visible Spectrum
Newton’s Colour Wheel
Spectral Colours
Dispersion of White Light
A Rainbow
Creating a Spectrum
Atomic Emission Lines
• An emission line is formed when an electron
makes a transition from a particular discrete
energy level of an atom, to a lower energy
state, emitting a photon of a particular energy
and wavelength.
• A spectrum of many such photons will show
an emission spike at the wavelength
associated with these photons.
Atomic Emission Principles
• When the electrons in the element are
excited, they jump to higher energy
levels.
• As the electrons fall back down, and
leave the excited state, energy is reemitted, the wavelength of which refers
to the discrete lines of the emission
spectrum.
Electron Excitation
The Hydrogen Atom
Hydrogen Tube and Emission
Bands
Emissions from an elemental gas
Emission Spectrum - H
Emission Spectrum - He
Emission Spectrum - Na
Emission Spectrum - Fe
Fireworks
• Red - Strontium and Lithium
salts
• Orange - Calcium salts
• Yellow - Sodium salts
Fireworks
• Green - Barium salts
• Blue - Copper salts
• Gold - incandescence of iron
and charcoal
• White - white hot metals
Spectral Lamps
• Sodium Lamp
• Potassium Lamp
• Cadmium Lamp
Spectral Lamps
• Helium Lamp
• Thallium Lamp
• Neon Lamp
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Spectral Lamps
• Zinc Lamp
• Rubidium Lamp
• Mercury Sulfide Lamp
Atomic emissions beyond the
visible spectrum
• Note that the emission extends over a range
of frequencies.
• The term often refers to the visible light
emission spectrum, although it extends to the
whole electromagnetic spectrum, from the
low energy radio waves up to high energy
gamma rays.
Atomic Absorption Lines
• An absorption line is formed when an electron
makes a transition from a lower to a higher
discrete energy state, with a photon being
absorbed in the process.
• These absorbed photons generally come
from background continuum radiation and a
spectrum will show a drop in the continuum
radiation at the wavelength associated with
the absorption.
Comparing different spectra
Astronomical Spectroscopy
• Involves the scientific exploration and
analysis of the properties of distant
objects
• Involves the observation of spectra at
very high spectral resolutions
Astronomical Spectroscopy
• Chemical elements can be detected in
astronomical objects by their emission lines
and absorption lines
• The shifting of spectral lines can be used to
measure the redshift or blueshift of distant or
fast-moving objects
• Helium was first discovered by spectral
analysis of light from the Sun
Absorption Spectrum of the
Sun
Hydrogen Absorption Spectrum
Origins of different Spectra
The Sun - A Nuclear Reactor
Formation of Deuterium as per
The Big Bang
Hydrogen Fusion in Stars
Nuclear Fusion to form Helium
- another possible mechanism
Nucleosynthesis in a Massive
Star
Spectral Classes of Stars