Lecture 3: What the Universe is Made Of

1
Lecture 3 What the Universe is Made Of

• Astronomy 5 The Formation and Evolution of the
  Universe
• Sandra M. Faber
• Spring Quarter 2007
• UC Santa Cruz

2
Visible light is composed of different
wavelengths.Each wavelength is a different color.
3
The electromagnetic spectrum
4
Objects look different in different
wavelengthsDifferent wavelengths measure
different things
Can you guess what wavelength this picture was
taken at?
Hint blue is dim, yellow is bright
5
Part of an EM wave frozen in space and time
x
6
Animation 1Propagating EM wave
7
Rough structure of an atom
8
Electron energy levels (orbitals) within an atom
are quantized
9
To make an electron jump up, the incoming photon
has to have the right energy when the electron
falls down, the same energy photon is emitted
Atoms can interact only with photons of
particular wavelengths. This set of wavelengths
is its fingerprint.
10
Animation 2Absorption and emission of a photon
11
Emission-line spectra from glowing gases of
different elements
Hydrogen
Helium
Mercury
Uranium
12
The visible-light spectrum of the Sun is wrapped
here end to end from red to blue. The dark
lines are wavelengths that are absorbed by
atoms in the Suns outer layers.
There are millions of lines in the Suns
spectrum.
The strengths of the lines are related to the
number of atoms of each element.
Modeling these features allows us to measure the
Suns composition.
13
Emission versus absorption spectra
14
Animation 3Emission vs. absorption spectrum
15
An emission and absorption spectrum side by side
Sun vs. glowing iron gas in laboratory. The
light from both has been passed through the same
apparatus.
The known iron wavelengths can be used to
calibrate the wavelengths of features in the
Suns spectrum.
16
Each element has its own spectral signature.
Nearly all the stable elements have been seen in
stellar spectra. This is how we know that the
rest of the Universe is made of the same stuff we
are.
17
A major recent discovery color bimodality