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

Spectra

Radiation and Spectra

Three types of spectra

What we can learn from spectra

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

Electromagnetic (EM) Waves

Gamma X-ray Ultraviolet Visible Infrared Microwave Radio

Radar TV FM AM

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 can you see?VISIBLE

Radar TV FM AM

• From fireflies, light bulbs 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

Electromagnetic (EM) Waves

Radar TV FM AM< 5 % of universe

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

Spectra

DR21 6000 ly 75 ly Cygnus

Looking with “other eyes”Ex: Newborn stars (IR)

Spectra

Visible Infrared

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

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 (handout)

SpectraContinuous

Emission

Absorption

Three Types of Spectra

Combinations

Spectra

Types of Spectra

Continuous, Emission, Absorption

Describe:

Spectra

Types of Spectra

Continuous, Emission, Absorption

Describe: Rainbow like, all λ

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:

Types of Spectra

Continuous, Emission, Absorption

Describe: Bright lines

Types of Spectra

Continuous, Emission, Absorption

Describe: Bright linesSource:

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:

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 linesSource:

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

Hot Dense Object

Hot Dense Object

Same lines

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

What can we learn from spectra?

1. Temperature (from color)

2. Composition (from spectra lines)

3. Density (from type)

4. Motion (from spectra shift)Doppler Shift lecture coming up