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Class Update• Observations
• Moon Phases• Due Tuesday, Mar. 3 (2 weeks)
• Tuesday, Feb. 17• 7:30-10pm Macalester College (Telescopes only)
• Friday, Feb. 20• 8-9:30pm University of Minnesota (Telesc. & Star Gazing [no Moon])
• Sunday, Feb. 22• 7:30-10pm Macalester College (Telescopes, Moon Craters, & Star
Gazing with Raquel)
• Grades updated yesterday, Feb. 16• Pick-up tests at end of lecture if you haven’t yet. Answers
posted outside office. Question 46: B or D is correct. Please notify of Scantron mistakes before you leave.
• No class Thu, Feb. 26 for Student Success Day – Please attend
Astro News• Rosetta spacecraft
– First close images of Comet 67p (Churyumov-Gerasimenko) • http
://www.universetoday.com/118981/the-first-images-are-in-from-rosettas-valentines-day-comet-flyby/#more-118981
– Comet 67p is outside Mars and will get closest to Sun in August (inside Mars orbit, outside Earth orbit)
– Philae landing on Comet 67p in November– http://sci.esa.int/where_is_rosetta/
• Mars and Venus near Moon this week– Venus brighter than Mars
Part of the above from http://library.thinkquest.org/10380/advanced.shtml
<5% of universe
VisibleROY G. BIV
Long λ (700 nm) (400 nm) Short λ Low f High f
Low energy High energy
Electromagnetic (EM) Spectrum
Ralph's Mother Is Visiting Uncle Xavier's GardenRadio Microwave Infrared Visible Ultraviolet X-ray Gamma
Which type of EM wave is generated from radioactive materials?GAMMA RAYS or gamma radiation
• Gamma rays are used in medical PET scans. • Most gamma rays are generated from universe.
Radar TV FM AM
Which type of EM wave is used to look at human bones?X-RAYS
• X-rays are used in airport security.• X-rays are emitted from hot gases in the universe.
Radar TV FM AM
Which type of EM wave causes sunburn, skin cancer, cataracts?
Radar TV FM AM
ULTRAVIOLET
• From “hot” objects in space (Sun and stars)
Which type of EM wave feels warm?INFRARED
Radar TV 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 FM AM
• Frequency of most wireless devices• From stars and gases
ALL EM WAVES:• Travel through the vacuum of space
(sound cannot)• Travel at the speed of light through the
vacuum of space
Earth’s atmosphere absorbs most EM waves
http://www.ipac.caltech.edu/outreach/Edu/Windows/irwindows.html
938 nm, 889 nm, 420 nm
Green – surface
Red – high atm, methane absorbs sunlight
Blue – violet wavelengths for the haze
Near IR 938 nmComposite visible
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
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 (handout)
Spectra
Types of Spectra
Continuous, Emission, Absorption
Describe: Rainbow like, all λ Source: Hot, dense object
Spectra
Types of 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: Bright linesSource: Excited gasEx: gas tube gas clouds in space
Spectra
Emission Spectra Compare spectrum of H to He
H spectrum is different than He spectrum
http://pixgood.com/helium-absorption-spectrum.html
Spectra
Emission Spectra
Each element has a unique spectrum.Different gases have different spectra.
Now know composition of stars!!!
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 linesSource: 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.
Spectra
What can we learn from EM spectra?
1. Temperature
2.
3.
4.
Composition
Density
http://www.jb.man.ac.uk/astronomy/nightsky/AList/Albireo.jpg
http://astro.unl.edu/naap/hr/hr_background1.html
What can we learn from spectra?
Density (from spectra type) = mass/volume– Continuous (rainbow)
• From a hot, dense object
– Emission (bright lines)• From a gas cloud
– Absorption (dark lines)• 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
SpectraNext time
• Blackbody radiation• Why lines in the spectra at all?• What do those lines mean?• Annie Cannon, Cecilia Payne