Astronomy Announcements & APOD: September 19, 2011 TA Help - PowerPoint PPT Presentation

Astronomy Announcements & APOD: September 19, 2011 TA Help Sessions: Sundays & Tuesdays HW #1 - Due NOW 6-8pm (room TBA) Quiz #1 - Wednesday

Blackbody Radiation BLACKBODY: Theoretical object that absorbs and re-radiates ALL wavelengths of light incident on it Blackbodies have a characteristic spectrum... Wavelength of Peak depends on Temperature!

Blackbody Radiation Approximate BLACKBODY: All real objects in thermal equilibrium (stable temperature) above absolute zero Wavelength of Peak depends on Temperature!

Blackbodies: Wavelength and Temperature Which has a higher temperature: A. Long wavelengths B. Short wavelengths

Blackbody Radiation Approximate BLACKBODY: All real objects in thermal equilibrium (stable temperature) above absolute zero Wavelength of Peak depends on Temperature! Wien’s Law

Stars as Blackbodies: E F Figure adapted from Prather et al, Lecture-Tutorials in Astronomy Which star gives off more blue light? Which star gives off more red light? Which star appears redder?

Blackbody Curves of Stars Energy Output (per second) (Flux, Intensity, Luminosity, Energy Density, etc.)

Einstein: PHOTONS are Quantizations of Energy The “Photoelectric Effect” PHOTONS: Particles of light carrying a set amount of energy (quantum of energy) that depends on wavelength (or f) of the light

Bohr’s Atomic Models • Electrons “orbit” protons & neutrons • Each “orbit” (shell) has a different energy • Exact energy depends on the atom

Close up: Bohr’s Hydrogen Atom • 1 proton (nucleus) • 1 electron (orbiting) • Many possible energy levels • Photons are emitted or absorbed when the electron change energy levels

Emission & Absorption Energy cannot be created or destroyed Absorption: a) Photon is absorbed by atom b) Electron moves UP (atom gains energy) Emission: a) Electron drops DOWN b) Photon is produced (atom loses energy)

Bohr’s Hydrogen Atom & Spectroscopy Balmer Series of Hydrogen - transitions to n=2 **Only See Photons @ Wavelengths Corresponding to Electron Energy Levels!

Bohr’s Hydrogen Atom & Spectroscopy Emission: Electron drops to lower energy levels Photons are produced

Matter: Bohr’s Hydrogen Atom Absorption: Electron raises to higher energy levels Photons are absorbed by atom (removed from spectrum)

Atomic Emission Spectra we can determine chemical composition of astronomical objects from their spectra!! Neon

EXAMPLE - Stellar Classification O B A F G K M

Example # 2: What element dominates here?

Kirchoff’s Laws: 3 Types of Spectra in Astronomy 1. Continuous 3. Absorption 2. Emission

Kirchoff’s First Law Hot, dense objects will produce a continuous spectrum.

Kirchoff’s First Law Hot, dense objects will produce a continuous spectrum.

Kirchoff’s Laws: 3 Types of Spectra in Astronomy 1. Continuous

Kirchoff’s Second Law Hot, low density gases will produce an emission spectrum.

Kirchoff’s Laws: 3 Types of Spectra in Astronomy II. Emission

Kirchoff’s Third Law Cool gases in front of a continuous source produce an absorption spectrum.

Kirchoff’s Laws: 3 Types of Spectra in Astronomy III. Absorption

Solar Spectrum - Which type?

Which type(s) of Spectra might you see here?