Transcript Spectra - MCTCteach.org

Objectives
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What kind of electromagnetic radiation comes from radioactive material? Is used to
look at bones? Causes skin damage? Can you see? Feels warm & penetrates
smoke & dust? Warms food? Can you hear?
How much of the universe can you see with your eyes, even with a telescope?
What is similar about these EM waves?
What is different about these EM waves?
Given a type of EM wave, give some idea of the energy of the source of that EM
wave. For example, does a radio wave come from a very energetic source or a
medium energy source or a not so energetic source?
Given a type of EM wave, give some idea of the temperature of the source of that
EM wave. For example, does a radio wave come from a cool, a warm, or a hot
source?
State the two kinds of EM waves that penetrate Earth’s atmosphere?
*Name and describe the three types of spectra.
*Describe a source or process that produces a continuous spectrum. An emission
spectrum. An absorption spectrum.
*Recognize that each element has a unique spectrum.
Define element.
Discuss how astronomers can tell what elements are in a gas cloud or in a star.
Spectra
Radiation and
Spectra
Three types of spectra
What we can learn from spectra
Electromagnetic (EM) Spectrum
 Long λ
Low f
Low energy
Visible
ROY G. BIV
(700 nm) (400 nm)
Short λ 
High f
High energy
<5% of universe
Ralph's Mother Is Visiting Uncle Xavier's Garden
Radio Microwave Infrared Visible Ultraviolet X-ray Gamma
Part of the above from http://library.thinkquest.org/10380/advanced.shtml
Electromagnetic (EM) Waves
Radar TV
FM
AM
Gamma X-ray Ultraviolet Visible Infrared Microwave Radio
Which type of EM wave is generated from radioactive materials?
GAMMA RAYS or gamma radiation
Radar TV
• Gamma rays are used in medical PET scans.
• Most gamma rays are generated from universe.
FM
AM
Which type of EM wave is used to look at human bones?
X-RAYS
Radar TV
FM
• X-rays are used in airport security.
• X-rays are emitted from hot gases in the universe.
AM
Which type of EM wave causes sunburn, skin cancer, cataracts?
ULTRAVIOLET
Radar TV
• From “hot” objects in space (Sun and stars)
FM
AM
Which type of EM wave can you see?
VISIBLE
Radar TV
• From fireflies, light bulbs and stars
FM
AM
Which type of EM wave feels warm?
INFRARED
Radar TV
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FM
AM
From our bodies and objects with heat
Used in TV remote controls and night vision goggles
Penetrates smoke and dust
Helps map dust between stars
Which type of EM wave warms food?
MICROWAVES
Radar TV
FM
AM
• Used to learn about the structure of nearby galaxies
Which type of EM wave can you play on your car stereo?
RADIO
Radar TV
• Frequency of most wireless devices
• From stars and gases
FM
AM
Electromagnetic (EM) Waves
< 5 % of universe
Radar TV
FM
AM
ALL EM WAVES:
• Travel through the vacuum of space
(sound cannot)
• Travel at the speed of light through the
vacuum of space
ALL EM WAVES
Differ in:
• λ
• f
• Energy
• Temperature
Earth’s atmosphere absorbs
most EM waves
http://www.ipac.caltech.edu/outreach/Edu/Windows/irwindows.html
Looking with “other eyes”
Ex: Newborn stars (IR)
Spectra
DR21
6000 ly
75 ly
Cygnus
Visible
Infrared
Spectra
Composite visible
Near IR 938 nm
938 nm, 889 nm, 420 nm
Green – surface
Red – high atm, methane
absorbs sunlight
Blue – violet wavelengths
for the haze
Titan (moon of Saturn) – NASA/JPL
To detect an EXTREMELY ENERGETIC
event like two neutron stars merging,
“look” for this kind of wave:
1. Radio
2. Micro
3. IR
4. Visible
5. UV
6. X-ray
7. Gamma
To detect a VERY LOW ENERGY event like
the spin flip of a H atom, “look” for this kind
of wave:
1. Radio
2. Micro
3. IR
4. Visible
5. UV
6. X-ray
7. Gamma
Spectra
**Waves carry energy,
hence, information.
λ (or color) tells you… Temperature
Ex: Star color tells you hot star or cool star
Spectra
From last lecture:
Spectrum – display of color or wavelengths
Spectra – plural
Wave Properties (Previous Lecture)
1. Speed
2. Wavelength
3. Frequency
4. Energy
What can we learn from spectra?
1. Temperature - from color (last lecture)
2.
3.
4.
What can we learn from spectra?
1. Temperature - from color (last lecture)
https://docs.kde.org/stable/en/kdeedu/kstars/ai-colorandtemp.html
What can we learn from spectra?
1. Temperature - from color (last lecture)
https://docs.kde.org/stable/en/kdeedu/kstars/ai-colorandtemp.html
What can we learn from spectra?
1. Temperature - from color (last lecture)
2. Composition - from spectra lines
3.
4.
Spectra
Diffraction Grating
– Spreads out the wavelengths
– Uses parallel lines to split and diffract light
– Same spectrum on both sides
– Ex: Show light bulb spectrum
Three Types of Spectra
Spectra
Continuous
Emission
Absorption
Combinations
Types of Spectra
Spectra
Continuous
, Emission, Absorption
Describe:
Types of Spectra
Spectra
Continuous
, Emission, Absorption
Describe: Rainbow like, all λ
Types of Spectra
Spectra
Continuous
, Emission, Absorption
Describe: Rainbow like, all λ
Source: Hot, dense object
Types of Spectra
Spectra
Continuous
, Emission, Absorption
Describe: Rainbow like, all λ
Source: Hot, dense object
Ex:
Filament of light bulb, surface of star
Types of Spectra
Continuous, Emission, Absorption
Describe:
Types of Spectra
Continuous, Emission, Absorption
Describe: Bright lines
Types of Spectra
Continuous, Emission, Absorption
Describe: Bright lines
Source:
Types of Spectra
Continuous, Emission, Absorption
Describe: Bright lines
Source: Excited gas
Ex: gas tube
gas clouds in space
Emission Spectra
Spectra
Compare spectrum of H to He
H spectrum is different than He spectrum
http://pixgood.com/helium-absorption-spectrum.html
Emission
Spectra
Each element
has a unique
spectrum.
Different gases
have different
spectra.
Now know
composition of
stars!!!
Spectra
Types of Spectra
Continuous, Emission, Absorption
Describe:
Emission
Absorption
Types of Spectra
Continuous, Emission, Absorption
Describe:
Dark lines
Missing colors
Missing λ
Continuous with missing λ
Types of Spectra
Continuous, Emission, Absorption
Describe: Dark lines
Source:
Types of Spectra
Continuous, Emission, Absorption
Describe: Dark lines
Source:
White light shining
through a gas or liquid
i.e. Light from a hot
dense object shining
through a gas or liquid
What can we learn from spectra?
1. Temperature (from color)
2. Composition (from spectra lines)
3. Density (from spectra type) = mass/volume
– Continuous (rainbow)
– Emission (bright lines)
– Absorption (dark lines)
4.
What can we learn Spectra
from EM spectra?
1. Temperature
http://www.jb.man.ac.uk/astronomy/nightsky/AList/Albireo.jpg
2. Composition
3. Density
4.
http://astro.unl.edu/naap/hr/hr_bac
kground1.html
Hot Dense Object
Hot Dense Object
Same lines
What can we learn from spectra?
Density (from spectra type) = mass/volume
– Continuous (rainbow)
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From a hot, dense object
– Emission (bright lines)
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From a gas cloud
– Absorption (dark lines)
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From a hot, dense object through a gas cloud
Spectrum of our sun
What type of spectrum?
What does that tell you about our sun?
ABSORPTION
SUN VIEWED THROUGH GAS CLOUD
(Sun’s atmosphere acts as a gas cloud)
Spectra
Next time
Spectra
• Blackbody radiation
• Why lines in the spectra at all?
• What do those lines mean?
• Annie Cannon, Cecilia Payne
What can we learn from spectra?
1.
2.
3.
4.
Temperature (from color)
Composition (from spectra lines)
Density (from type)
Motion (from spectra shift)
Doppler Shift lecture coming up
Observation: Planetarium
• Start: Observing Project: Planetarium Feb. 14
• Due: May 4
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Class Field Trip
To: Como Planetarium
When: Tue. Mar. 21
Shows at 8:40am (section 1) and 9:50am (section 2)
Bus times:
• Leave MCTC at 8am or 9:15am
• Return to MCTC about 10am or 11:15am
• If you can’t go on the field trip, then go on your own
time. See calendar for options
Homework & Observations
• Observations
• Sunset Part 1 – Due TODAY, Tuesday, Feb. 14 by
midnight by email
• Moon Phases – Due Thursday, Mar. 2
• Telescopes, Star Gazing & Moon Craters – See Calendar
• No Moon Craters at locations this week
• Keep up with Objectives at the beginning of
each lecture
Number of Students
Test 1 Results
16
16
A
B
20
C
Letter Grade
15
14
D
F
• 81 students: 75 students took the test; 6 didn’t take it (F)
• High was 58/60 so it was curved by 2 points
• Average is a C at 73% after curve (44/60)