4. Finger print of atom
•As similar as human, each atom (and molecule) also has a “fingerprint” called spectrum(光谱)
氢
氦
氖
钠
汞
•We can learn what atom is included in the
stars, galaxies and gas in the universe by using
spectrum.
5. What is spectroscopy
•When the light goes into a prism, the light is divided into spectrum(光谱) according to its
wavelength.
•The spectroscopy(光谱学) is to divide the light into spectrum.
6. Continuum spectrum and line spectrum
•There are 3 types of spectrum.
1. Continuum spectrum(连续光谱)
•The spectrum is continuous.
3. Emission spectrum(发射谱)
•The absorption line appears at a
specific wavelength
2. Absorption spectrum(吸收谱)
•It is similar to the absorption line. The absorption line also appears at a specific
wavelength
8. •Emission line appears in the atomic spectrum. We first consider emission lines from an atom.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Excited state (high energy state) Ground state (low energy state)
•The hydrogen atom in the excited state is higher energy than the ground state
Transition
Electromagnetic wave
Emission lines
9. •Emission line appears in the atomic spectrum. We first consider emission lines from an atom.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Excited state (high energy state) Ground state (low energy state)
•The hydrogen atom in the excited state is higher energy than the ground state
Transition
•When a hydrogen atom in the excited state transitions from the excited state to the ground
state, the hydrogen emits an electromagnetic wave.
Electromagnetic wave
Emission lines
10. •Emission line appears in the atomic spectrum. We first consider emission lines from an atom.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Excited state (high energy state) Ground state (low energy state)
•The hydrogen atom in the excited state is higher energy than the ground state
Transition
•When a hydrogen atom in the excited state transitions from the excited state to the ground
state, the hydrogen emits an electromagnetic wave.
Electromagnetic wave
Emission lines
11. Emission lines
•We first consider emission lines from an atom.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Excited state (high energy state) Ground state (low energy state)
Transition
•This emitted electromagnetic wave appears as an emission line.
12. Emission lines
•We first consider emission lines from an atom.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Excited state (high energy state) Ground state (low energy state)
Transition
•This emitted electromagnetic wave appears as an emission line.
13. •The mechanism of absorption line mechanisms is similar to the emission.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Transition
Electromagnetic wave
Absorption lines
Ground state (low energy state)
Excited state (high energy state)
•We next consider hydrogen atom at grand state
14. •The mechanism of absorption line mechanisms is similar to the emission.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Transition
Electromagnetic wave
Absorption lines
Ground state (low energy state)
Excited state (high energy state)
•The hydrogen atom at the ground state transitions to an excited state by absorbing
electromagnetic wave.
•We next consider hydrogen atom at grand state
15. •The mechanism of absorption line mechanisms is similar to the emission.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Transition
Electromagnetic wave
Absorption lines
Ground state (low energy state)
Excited state (high energy state)
•The hydrogen atom at the ground state transitions to an excited state by absorbing
electromagnetic wave.
•We next consider hydrogen atom at grand state
16. •The mechanism of absorption line mechanisms is similar to the emission.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Transition
Absorption lines
Ground state (low energy state)
Excited state (high energy state)
•This absorbed electromagnetic wave appears as absorption line.
17. •The mechanism of absorption line mechanisms is similar to the emission.
Hydrogen atom（氢⽓)
Proton Proton
Electron
Transition
Absorption lines
Ground state (low energy state)
Excited state (high energy state)
•This absorbed electromagnetic wave appears as absorption line.
18. Emission line from gas
•Because hot gas and stars in the universe consist of atoms, they emit emission lines.
Since each atom has own emission lines, we can learn what atom is contained in
the hot gas and stars via emission lines.
•An example of emission lines from galaxy
19. Absorption line from gas
•If there is cold gas between hot gas or stars and us, we can observe absorption lines.
•From the absorption lines, we can learn the status of cold gas.
•The absorption lines appeared in the spectrum of
cold gas
20. Amino acid(氨基酸)
Life in the universe and molecule
•Our body consists of protein(蛋⽩质) linked to amino
acid(氨基酸)
•When we would like to find life in the universe, we need
to look for an amino acid in the universe.
•For this purpose, we focus on emission lines from
molecules.
21. •We have already found organic molecules （有机分⼦） which is related to amino acid
in the universe by using spectroscopy.
Life in the universe and molecule
•In future astronomy, we would like to find amino acid which consists of human body.
22. The application of spectroscopy
•The emission lines are shifted by the Doppler effects
•If objects are moving towards the observer,
the wavelength of the emission line becomes
shorter.
•If objects are moving away from the
observer, the wavelength of the emission line
becomes longer.
26. Wavelength
The application of spectroscopy
•By using the Doppler effect of emission lines, we can learn the velocity of stars,
galaxies and gas.
•E. Hubble found the expansion of the universe
by observing spectroscopy of galaxies.
Velocity
Distance from Milky Way
(Example)
27. Summary
• The spectrum is
fi
ngerprint of an atom.
• There are 3 kinds of spectrum types. Continuum,
emission line, and absorption line.
• We can learn the status of stars, galaxies, and gas by
observing the spectrum.
