1 Announcements Astronomy 101A 10/05/11 TJacobsen Observatory 8:30 - 9:30 pm OPTIONAL (especially if it is not clear) TReview for exam 1 on Friday; exam 1 Monday, 10/10 –Will have summer’s exam on-line soon (will announce) for study purposes –Mix of short answers, fill in blanks, short essay, reading star map, vocabulary TExercise on spectral analysis in sections tomorrow - important for next 2 weeks! (and, your scores)

2 Wavelength (meters)

3 If we could see at IR wavelengths, what would we see? Radio waves Infrared Radiation Microwaves

4 Ultraviolet A, B, C X-Rays Gamma Rays The Sun’s UV rays can cause: * More wrinkles * Sagging skin * Age or liver spots * Tan/sunburn * Eye damage/ cataracts * Skin Cancer

5 Messier 82 (M82) optical infrared Color Coded: Blue - x-ray Red - optical Green - wavelength = 3 mm CO molecule (H 2 )

6 o Define light (electromagnetic radiation) and describe how we characterize it o List 3 ways that light is created o Explain why stars appear to be different colors and how we use this property o Distinguish between emission and absorption spectra by what is happening with the electron in the atom. Learning goals

7 o Define light (electromagnetic radiation) and describe how we characterize it o List 3 ways that light is created o Explain why stars appear to be different colors and how we use this property o Distinguish between emission and absorption spectra by what is happening with the electron in the atom. Learning goals

8 Light measured in wavelength, frequency  or photon energy; light has the velocity c in a vacuum Why are outer ends “black”? Define light (electromagnetic radiation) and describe how we characterize it

9 Light can behave as a wave OR a PARTICLE! E = h [Planck’s Constant: Energy Frequency (nu) RODS & CONES

10 Oscillation of electric and magnetic fields Propagates through space and some materials Electromagnetic Radiation: o- blackbody radiation (thermal) o- emission as electrons lose energy in an atom o- electrons spiraling in a magnetic field Produced By: Define light (electromagnetic radiation) and describe how we characterize it List 3 ways that light is created (astronomically speaking)

11 o Define light (electromagnetic radiation) and describe how we characterize it o List 3 ways that light is created.

12 o Define light (electromagnetic radiation) and describe how we characterize it o List 3 ways that light is created o Explain why stars appear to be different colors and how we use this property o Distinguish between emission and absorption spectra by what is happening with the electron in the atom. Learning goals Please take out a full sheet of paper, and put your name, and section (or TA’s name) at the top. Unannounced participation activity!

13 Continuous Spectrum - created by thermal radiator (blackbody radiation) Hotter stars look more blue-white than cooler stars because hot stars emit most of their light at shorter wavelengths. Wien’s Law Star field in Sagittarius Explain why stars appear to be different colors and how we use this property

14 Tutorial: Blackbody Radiation Violet, green/yellow, red; very little blue or yellow/orange. a)

15 Stars A & B C When objects emit light over all wavelengths, they look white, so star A will be whitish. Star C is emitting loght mostly in yellow/red, so will look “redder.”

16 Different surface temperatures

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19 o Define light (electromagnetic radiation) and describe how we characterize it o List 3 ways that light is created o Explain why stars appear to be different colors and how we use this property o Distinguish between emission and absorption spectra by what is happening with the electron in the atom. Learning goals

20 Physical processes behind emission and absorption by atoms (representation of hydrogen energy levels): Energy level

21  Distinguish between emission and absorption spectra by what is happening with the electron in the atom.

22  Distinguish between emission and absorption spectra by what is happening with the electron in the atom.

23 IdealizedRealistic  Distinguish between emission and absorption spectra by what is happening with the electron in the atom.

24 Emission vs absorption spectra T T T T T T T T T T