Download Absorption spectrum

Weekly Schedule Today
•  Finish LT and go over •  Electromagne:c spectrum –  Lecture Tutorials •  Lab # 3-­‐ Spectral Analysis Lab Next Thursday Hw # 3 Quiz # 3 Light cont. Doppler effect Reminder: Exam # 1 in one week! •  I’ll post a study guide! • 
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Electromagne:c radia:on Almost
everything we
know about the
universe comes
from analysis of
EM
I.e. The Transmission of energy through space Example: Light
EM energy transmiQed as waves Need to know: wavelength, amplitude, period, frequency
http://media.pearsoncmg.com/aw/aw_0media_astro/if/if.html?anatomy_of_a_wave
2.2 Waves in What?
Water waves, sound
waves, and so on,
travel in a medium
(water, air, …).
Electromagnetic
waves need no
medium.
Created by
accelerating charged
particles
Rela:onships Frequency: Number of wave crests that pass a given point per second
Period: Time between passage of successive crests
Period = 1 / Frequency
Wavelength: Distance between successive crests
Velocity: Speed at which crests move
Velocity = Wavelength / Period
(Wavelength) x (Frequency) = velocity
Frequency is measured in Hertz (cycles/second) Problem. •  Find the wavelength of your groups favorite radio sta:on (measured in MHz) •  Hint: Velocity (c)= 300,000 km/s f=c/λ Energy and wavelength are
related….
E = h c
λ
1
0.25 =
1
2
4
Inverse relationship
0.5 =
E = energy
h = Constant (Planck’s constant)
c = constant (speed of light)
λ = wavelength of photon (m)
Cooler:
-Longer wavelength
(yellow)
-Lower energy
Hotter:
-Shorter wavelength
(blue)
-Higher energy
Energy and
wavelength
are
related….
The Electromagnetic Spectrum
Different colors of light are distinguished by their
frequency and wavelength.
The visible spectrum is
only a small part of the
total electromagnetic
spectrum.
Electromagne:c spectrum *Dis:nguished by frequency and wavelength http://
media.pearsoncmg.com/
aw/aw_0media_astro/if/
if.html?em_spectrum
Things to note about the Eletromagnetic
Spectrum
•  atmosphere is only transparent at a few
wavelengths – the visible, the near infrared, and
the part of the radio spectrum with frequencies
higher than the AM band
•  atmosphere is absorbing a lot of the
electromagnetic radiation impinging on it
•  Horizontal scale is logarithmic – each tick is a
factor of 10 smaller or larger than the next one.
http://media.pearsoncmg.com/aw/aw_0media_astro/if/if.html?light_absorption
Sunlight reaches Earth's atmosphere and is
scattered in all directions by all the gases and
particles in the air. Blue is scattered more than
other colors because it travels as shorter, smaller
waves. This is why we see a blue sky most of the
time.
As the Sun gets
lower, its light is
passing through
more of the
atmosphere. Even
more of the blue
light is scattered,
allowing the reds
and yellows to
pass straight
through to your
eyes.
Which of the following travels the slowest? Radio waves Visible light X-­‐rays Infrared light They all travel the same speed 57%
29%
14%
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Which of the following is not a form of light? Radio waves Microwaves X-­‐rays All of the above None of the above 57%
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Radia:on Laws •  Temp-­‐ amount of mo:on •  F = 9/5C + 32 •  Kelvins = C + 273 Thermal Radiation
Intensity: amount or strength of radiation
Blackbody spectrum: Radiation emitted by an
object over a range of frequencies
* Not
symmetrical;
falloff more
rapid at high
frequency side
for all object
Blackbody curves Energy output (y-­‐axis) Wavelength (x-­‐axis) *Can reveal temperature (and size) informa:on *No:ce how the curves shii towards higher frequencies with increasing temperature. What’s the wavelength doing? http://media.pearsoncmg.com/aw/
aw_0media_astro/if/if.html?wiens_law
Wien’s Radia:on Laws: Peak wavelength α 1/temperature Stefan’s Law: Energy α temperature4 •  The star Veritas is observed to have a blue-­‐white light of peak wavelength 450 nm, and the star Erasmus is observed to have a deep reddish light of peak wavelength 720 nm. •  Which star is hoQer? HoQer it is, the bluer it is, the more energy it has The graph at right shows the blackbody spectra for three different stars. Which of the stars is at the highest temperature? 58%
Peak wavelength ~ 1/temperature Energy ~ temperature4 33%
ar
C
St
ar
B
St
ar
A
8%
St
1.  Star A 2.  Star B 3.  Star C A lump of lead is heated to a high temperature. Another lump of lead that is twice as large is heated to a lower temperature. Which lump of material appears bluer? 100%
The cooler lump appears bluer. The hoQer lump appears bluer. Both lumps look the same color. Cannot tell which lump looks bluer. p ..
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Astronomical Implica:ons •  Young stars emit infrared/radio radia:on because they are cooler •  The brightest stars emit ultraviolet radia:on because of their high surface temperature http://media.pearsoncmg.com/aw/aw_chaisson_astronomytoday_6/videos/ch03/
OrionNebMultispectral.html
PRODUCING A CONTINUOUS SPECTRUMSpectroscope: Splits light into component colors
A continuous spectrum is produced by a hot, high-density light source.
PRODUCING AN EMISSION (Light) SPECTRUM
Emission lines:
Single
frequencies
emitted by
particular atoms
What’s the black
showing?
All wavelengths
not emitted!
An emission spectrum is produced by a
hot, low-density light source.
EMISSION SPECTRA TELL US CHEMICAL
COMPOSITION OF STARS
Figure 2.16
PRODUCING AN ABSORPTION
(Dark line) SPECTRUM
An absorption spectrum is produced by a hot,
high-density light source shining through a cool,
low-density medium. Or by looking at the SUN
through a prism!!!
http://media.pearsoncmg.com/aw/
aw_0media_astro/if/if.html?
illustrating_kirchhofs_laws
Absorption spectrum: If
a continuous spectrum
passes through a cool
gas, atoms of the gas
will absorb the same
frequencies they emit.
THIS IS THE SUN’S SPECTRUM.
THE SUN’S SPECTRUM IS ______.
Which of the following spectra is produced by the Sun? 90%
1.  Dark line absorp:on spectrum 2.  Bright line emission spectrum 3.  Con:nuous spectrum 10%
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Imagine that you observe the Sun while in your space ship far above Earth’s atmosphere. Which of the following spectra would you observe by analyzing the sunlight?
50%
1.  dark line absorp:on spectrum 33%
2.  bright line emission spectrum 3.  con:nuous spectrum 17%
Imagine that you are on the surface of Earth (below the atmosphere) and are observing the 89%
Sun. Which of the following spectra would you observe by analyzing the sunlight? 1.  dark line absorp:on spectrum 2.  bright line emission spectrum 3.  con:nuous spectrum uo
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Stop Bohr’s Model of the Atom explained the
observations of “Line Spectra”
~700nm
A
M
F
M
T
V
Micr
owav
e
Infrared
Ultraviolet
~350nm
X-Rays
Gamma-Rays
Bohr’s model of the atom
This model of the atom nicely
explains many phenomena.
For example:
Emission Spectra
As you heat up an atom, all the
electrons absorb the heat and thus gain
Kinetic Energy.
This moves
the electrons
out to higher
orbitals.
As you heat up an atom, all the
electrons absorb the heat and thus gain
Kinetic Energy.
This moves
the electrons
out to higher
orbitals.
As electrons are allowed only
in certain orbitals, they can
only fall certain, well defined
“distances”.
This gives the us
the well defined
spectral lines that
we saw in lab
yesterday.
Bohr’s Model of the Atom explained the
observations of “Line Spectra”
~700nm
A
M
F
M
T
V
Micr
owav
e
Infrared
Ultraviolet
~350nm
X-Rays
Gamma-Rays
Which drawing represents the process by which and absorp:on line is formed? 1. 
2. 
3. 
4. 
A B C D Which drawing represents the process by which an emission line is formed? 1. 
2. 
3. 
4. 
A B C D 10
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Is this atom
absorbing or
emitting energy?
What type of
spectrum will it
produce?
Doppler Effect Red shii = moving away Blue shii = moving towards Measured
in a lab
A bright star is moving away from Earth. Which of the choices best completes the following statement describing the spectrum of this star? A(n) ___________ spectrum that is _______ rela:ve to 20% 20% 20% 20% 20%
an unmoving star. pt
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absorp:on; blueshiied emission; redshiied con:nuous; blueshiied absorp:on; redshiied con:nuous; redshiied a
1. 
2. 
3. 
4. 
5. 
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Which object is at rest? T
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O
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20% 20% 20% 20% 20%
O
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Object A Object B Object C Object D They are moving the same speed, the speed of light O
bj
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t A
1. 
2. 
3. 
4. 
5. 
10
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Which of the objects is moving with the fastest speed? n.
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10
T
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O
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20% 20% 20% 20% 20%
O
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Object A Object B Object C Object D They are moving the same speed, the speed of light O
bj
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1. 
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5. 
Countdown