Class Update D2L Quiz 5 available; Quiz 6 on Tuesday; Questions on Test 2 Observations Moon Phases Due Tuesday, Mar. 3 (2 weeks) Friday, Feb :30pm University of Minnesota (Telesc. & Star Gazing [no Moon]) Sunday, Feb. 22 (Dress Warmly – hat, gloves) 7:30-10pm Macalester College (Telescopes, Moon Craters, & Star Gazing with Raquel) to reserve your spot in my car if you want a ride to and from MCTC. Meet at Café Espresso Royale at 6:45pm. Macalester Olin Science Building 4 th floor, southwest corner Street Parking off side streets of Snelling (Osceola & Fairmont) No class Thu, Feb. 26 for Student Success Day – Please attend Mars and Venus near Moon Friday night (show in Starry Night) –Venus brighter than Mars

Blackbody Radiation Atoms and Light 1 3 2

Spectra Blackbody Radiation Definition: Radiation emitted by a heated object When not heated, the object is black When heated, the object varies in color depending on the temperature Continuous spectrum A black body absorbs and emits radiation

Spectra Blackbody Radiation Examples: Incandescent light bulb Filament changes color as it is heated Hot lava Sun and other stars Heated metal Quickly heated ice cube glows

Light Bulb Filament Solve: Are there vibrations of the atoms in the filament? 1. Are there many atoms or a few atoms in the metal filament? MANY ATOMS

1. MANY ATOMS in the metal filament. 2. True or False: Each atom vibrates at some frequency. TRUE Light Bulb Filament Solve: Are there vibrations of the atoms in the filament?

1. MANY ATOMS in the metal filament. 2. Each atom VIBRATES at some frequency. Light Bulb Filament Solve: Are there vibrations of the atoms in the filament? 3. True or False: All atoms vibrate at the same frequency. FALSE Not all vibrate at the same frequency Many different frequencies

1. MANY ATOMS in the metal filament. 2. Each atom VIBRATES at some frequency. Light Bulb Filament Solve: Are there vibrations of the atoms in the filament? 3. Atoms vibrate at the DIFFERENT frequencies. Different frequencies correspond to different wavelengths and display different colors. Blue light = 400 nm Red light = 700 nm

Spectra Blackbody Radiation Examples: lee/java/bb_mjl.htm Side Note: Intensity = Energy/surface area Temperature α Energy

Which star is hottest? How do you know?

Hotter object has: More overall radiation (intensity) Higher peak Which star is hottest? How do you know?

Spectrum of the Sun What do you know from this spectrum? Absorption – hot dense object with a gas cloud Mix of gases (but which ones?)

Spectra Other stars show similar but not identical line patterns. So why are there lines in the spectra at all? What do those lines mean?

Spectra of stars (differences)

Intensity difference

Line differences are element differences

Spectra Annie Cannon Harvard, turn of the last century Sorted thousands of stars by their patterns of spectra lines. Discovered patterns among star spectra Lines are different for different elements λs?, visible?, Temperatures? Longer λ UV Hotter Cooler

Spectra Annie Cannon OBOB A F G M K { { { { { { Hotter Cooler Lines used to categorize wavelength & temperature Still used today and extended past M for darker red and brown stars. Blue Red

Spectra So why are there lines in the spectra at all? And What do those lines mean?

Spectra Definitions Atom –Basic unit of a chemical element –Has protons, neutrons, & electrons Element –More than 100 substances that cannot be broken down any simpler Molecule –Group of atoms

Spectra Atoms Protons – positive charge ( + ); larger mass Neutrons – neutral, no charge; larger mass Electrons – negative charge ( - ); smaller mass Nucleus –protons and neutrons Surrounded by –“orbiting” electrons

Quantum Mechanics Study of atoms and subatomic particles 1. Electrons have certain “orbits” and not others 2. Orbits are closer together as you get further from the nucleus Ground state - Lowest energy level Bohr Model

Quantum Mechanics When an electron jumps “down”, it emits all the energy at once in a bundle called a photon (the energy is quantized). If an electron absorbs a photon of just the right energy, it jumps “up”. Absorb = take in (ex. Increase energy) Emit = give off (ex. Decrease energy)

Of the electron jumps shown, which number of jump EMITS (gives off) a photon? 2 and 3 Decrease in energy

Of the electron jumps shown, which number of jump ABSORBS (takes in) a photon? 1 Increase in energy

For the atom shown, a blue and a green photon are emitted and a red photon is absorbed. Which jump corresponds to emitting a blue photon? Which jump corresponds to emitting a green photon? Which jump corresponds to absorbing a red photon? For the atom shown, a blue and a green photon are emitted and a red photon is absorbed. Which jump corresponds to emitting a blue photon?2 Which jump corresponds to emitting a green photon?3 Which jump corresponds to absorbing a red photon?1

Cecilia Payne-Gaposchkin Surveyed star spectra Discovered stars are about 90% hydrogen and 10% helium