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Transcript
```Goal: To understand how light is
used to understand what
astronomy.
Objectives:
1) To learn the Properties of light
2) To understand how the 3
different types of spectra are
created.
3) Play the GUESS THE GAS
CONTEST!!!
Properties of light
• Light can act like either a particle or a
wave. Most commonly acts like a wave.
• Like waves you are familiar with, light
waves have a wavelength and energy.
• Energy = a constant * speed of light / wavelength
Which of the following would NOT
emit light waves?
•
•
•
•
•
•
•
Dentist X-ray machine
The night side of the moon
Neon sign
All of the above emit light
None of these emit light
Region
Wavelength
(Angstroms)
Wavelength
(centimeters)
Frequency
(Hz)
Energy
(eV)
> 109
> 10
< 3 x 109
< 10-5
Microwave
109 - 106
10 - 0.01
3 x 109 - 3 x 1012
10-5 - 0.01
Infrared
106 - 7000
0.01 - 7 x 10-5
3 x 1012 - 4.3 x 1014
0.01 - 2
Visible
7000 - 4000
Ultraviolet
4000 - 10
4 x 10-5 - 10-7
7.5 x 1014 - 3 x 1017
3 - 103
X-Rays
10 - 0.1
10-7 - 10-9
3 x 1017 - 3 x 1019
103 - 105
Gamma Rays
< 0.1
< 10-9
> 3 x 1019
> 105
7 x 10-5 - 4 x 10-5 4.3 x 1014 - 7.5 x 1014
2-3
A radio wave is sent out from
planet earth. How long will it take
that radio wave to travel to Alpha
Centauri B (4.3 light years away)
•
•
•
•
•
A) a little over 1 year
B) a little over 2 years
C) a little over 4 years
D) a little over 8 years
E) this radio wave can’t possibly get there.
How is light created?
• Light is created by electrons changing
energy states – to conserve energy.
• So, to understand light, you have to
understand the atom.
• Atoms are made of a nucleus (with +
charged protons and uncharged neutrons)
and shells of – charged electrons.
• Much like different distances from an object
creates a difference gravitational energy, so
to does the distance from a nucleus.
• However, there are only certain specific
allowed energy states in an atom.
Spectra, meet the spectra!
• There are 3 types of spectra:
• 1) continuous – a smooth light curve with
no breaks and light at all wavelengths
• 2) absorption – a continuum which has
parts taken out (kind of like a hockey
goalie).
• 3) emission – either a continuum with
emission added to it, or just a series of
special lines.
Condescend Light Bulb
• Take the spectral glasses and take a look
at the Condescend light bulb. What type
of spectrum would you classify this as?
• A) Continuous
• B) Absorption
• C) Emission
Blackbody Spectrum – continuous
• All objects which absorb most of the light
which passes through them emit energy
as a “blackbody”. The shape of the
blackbody spectrum is always the same.
• The strength of the spectrum (i.e. how
much light it emits) and the peak
wavelength of the spectrum depend on the
temperature of the object.
http://theory.uwinnipeg.ca/users/gabor/foundations/quantum/slide6.html
Windex
•
•
•
•
What type of spectrum does this produce?
A) Continuous
B) Absorption
C) Emission
Absorption Spectrum
• As you can see, the Windex creates a
spectrum where you have a continuous
portion, but a huge chunk is taken out.
• This chunk is absorbed by the Windex.
• The Windex, not surprising, is blue
because of the light it absorbs.
Absorption spectra in Astronomy
• Windex is a solution of very complex molecules
though, and in Astronomy most Absorption
spectra are created by gasses of a few atoms
and few molecules.
• Therefore, most Absorption spectra in
Astronomy consist of thin dark lines, or thin
areas where most of the energy is removed at
just a few wavelengths.
• Any “thin” substance which is in front of a
continuous light source will produce an
absorption spectrum IF it is cooler than the
continuous source.
Absorption – our use
• When you find an emission or absorption
spectrum, you know what the makeup of
the gas or material that emitted it.
• Each element and each molecule have
their own specific energies they can emit.
This is a fingerprint of the gas.
• This is why we know the sun is made of
mostly H and He.
Fluorescent lights
•
•
•
•
What type of spectrum does this produce?
A) Continuous
B) Absorption
C) Emission
Fluorescent lights
• This is emission.
• The electrons in the gas get “excited” by the
energy put through the gas.
• The electrons then “cascade” down to emit
several photons of light. One is a optical photon.
• There are different specific energy states, and
the lines are produced by the different
combinations of energy states (starting/ending).
• Any thin gas will produce an emission spectrum
if you JUST look at the gas.
• Any thin gas which is HOTTER than a
background continuous source will ALSO
produce emission features!
Guess the gas contest!
• For each of the following tubes you may
find it helpful to draw the pattern of light.
You will guess which gas is in each tube.
• Anyone who can get all of them gets a
bonus 5 points!
• Everyone who turns in with guesses and
patterns on all tubes gets the normal
points.
• If you can get all but 1 I will give you a
bonus 3 points.
• If you get 4 of 6 you get 1 bonus point.
Conclusion
• We examined the properties of light.
• We discovered the method of creating
light.
• We discovered the different spectrum and
explored how to create each one of them
(and therefore what we can use them for).
• We looked at some gasses and found
what most of them were from the light they
emitted.
```
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