Class Update Observations Moon Phases Due Tuesday, Mar. 3 (2 weeks) Tuesday, Feb. 17 7:30-10pm Macalester College (Telescopes only) Friday, Feb :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) in-from-rosettas-valentines-day-comet-flyby/#more http:// in-from-rosettas-valentines-day-comet-flyby/#more –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 – 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 <5% of universe Visible ROY 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 Garden Radio 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

Spectra DR 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)

What can we learn from spectra? 1. Temperature - from color (last lecture)

What can we learn from spectra? 1. Temperature - from color (last lecture)

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 Continuous 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 lines Source:

Types of Spectra Continuous, Emission, Absorption Describe: Bright lines Source: Excited gas Ex: gas tube gas clouds in space

Spectra Emission Spectra Compare spectrum of H to He H spectrum is different than He spectrum

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 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.

Spectra What can we learn from EM spectra? 1.Temperature Composition Density kground1.html

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 Next 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