Download Understanding Light: Wave-Particle Duality, Spectrum, and Interaction with Matter - Prof. and more Study notes Astronomy in PDF only on Docsity! ASTR1030 - FALL, 2008. LECTURE 12; PAGE 1 ASTR1030 Announcements http://lasp.colorado.edu/~ergun/ ASTR1030/ Next Observing: Thursday, Oct. 2, 7:30 pm. SBO. • This weeks reading: Chapter 6. Today • LIGHT! ASTR1030 - FALL, 2008. LECTURE 12; PAGE 2 Light: The “Wave-Particle Duality” Waves : . Frequency Wavelength× Speed= f λ× c= ASTR1030 - FALL, 2008. LECTURE 12; PAGE 5 Light Spectrum Ultraviolet Radiation has frequencies greater than that of visible light (shorter wavelengths). We cannot sense ultraviolet radiation, but after exposure, we can feel it’s effects (sunburn). X rays have frequencies greater than that of ultraviolet (shorter wavelengths). We cannot sense X rays. Many materials are transparent to X rays (i. e., they look like glass or water to someone with X-ray vision), so X rays are very use- ful to “look” inside an object. Gamma Rays have frequencies greater than that of X rays. Individual gamma ray photons have a lot of energy and can damage a cell if they strike it - making them dangerous to humans. ASTR1030 - FALL, 2008. LECTURE 12; PAGE 6 Light Interaction with Matter There are four basic ways in which light can interact with matter: 1. Emission 2. Absorption 3. Transmission 4. Reflection ASTR1030 - FALL, 2008. LECTURE 12; PAGE 7 Light: Emission ALL OBJECTS EMIT LIGHT! The emitted light generally covers a large range in the spectrum. The peak in the spectrum is proportional to the temperature. λpeak 2.9 10 6× T ---------------------- Knm o( )= ASTR1030 - FALL, 2008. LECTURE 12; PAGE 10 Light: Emission What is the spectral peak of light emitted from our body? What is the spectral peak of light emitted from the sun? Important Point: We can tell how hot stars are from their color. λpeak 2.9 10 6× T ---------------------- Knm o( )= λpeak 2.9 10 6× 300 K o ---------------------- Knm o( )= λpeak 10 4 nm (Infared)= λpeak 2.9 10 6× 5800 K o ---------------------- Knm o( )= λpeak 500nm (Yellow)= ASTR1030 - FALL, 2008. LECTURE 12; PAGE 11 Light: Emission Every substance has a distinct emission pattern or finger print. Important Point: We can tell what a planet or star is made of by analyzing the emission spectrum. Magnified View ASTR1030 - FALL, 2008. LECTURE 12; PAGE 12 Light: Absorption/Transmission Every substance has a distinct absorption pattern or finger print. Important Point: We can tell what a gas is made of by analyzing the absorption spectrum. Magnified View tar Cloud ASTR1030 - FALL, 2008. LECTURE 12; PAGE 15 Light: Detecting Planets ASTR1030 - FALL, 2008. LECTURE 12; PAGE 16 Light Doppler Shift Example: The 557.7 nm O+ green line is from a comet is seen at 557.8 nm. Is Jupiter moving toward or away from us? How fast in km/s? A: Away. The wavelength is longer, so the light is red-shifted. v c -- λshift λlaboratory– λlaboratory ------------------------------------------= v c ∆λ λ0 ------= v c ∆λ λ0 ------ 3 10 8 m s⁄×( ) 0.1nm 557.7nm -------------------- 5.4x10 4m s --- 54 km s ------= = = = ASTR1030 - FALL, 2008. LECTURE 12; PAGE 17
