Astronomy 1010 Planetary Astronomy Fall_2014 Day-17

Course Announcements Smartworks Chapter 4: Mon. 10/06 SW Ch. 5: Fri. 10/10 (see, it did change) SW Ch. 6: Fri. 10/24 (subject to change) Exam-2: Friday, Oct. 10 (Ch. 3, 4, 5) Read chapters 5, 6

 The spectrum of a cloud of glowing gas contains emission lines.  When viewed through a cloud of gas, a continuous spectrum will have absorption lines.

 The wavelengths at which atoms emit and absorb radiation form unique spectral fingerprints for each atom.  They help determine a star’s composition, temperature, and more.

 Knowing the speed of light and one other variable, either the wavelength or frequency of the light in question, you can find the remaining quantity.  Example: Find the wavelength of the light wave coming from a radio station broadcasting on 770 AM: MATH TOOLS 5.1

Lecture Tutorial Light & Atoms: (pg. 65) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group.

Concept Quiz—Energy Levels In the energy level diagram, transition B has half the energy of transition A. What is the wavelength of emitted light? A. 225 nm B. 450 nm C. 900 nm A: = 450 nm B: = ?

 The motion of a light source toward or away from us changes our perception of the wavelength of the waves reaching us.  Doppler effect.

 Light from approaching objects is blueshifted; the waves crowd together.  Light from receding objects is redshifted; the waves are spaced farther apart.

Doppler Shifts Redshift (to longer wavelengths): The source is moving away from the observer Blueshift (to shorter wavelengths): The source is moving towards the observer  = wavelength shift o = wavelength if source is not moving v = velocity of source c = speed of light

 If you know the wavelength of light you are observing as well as the wavelength of light the object would be emitting if it were at rest, you can find the speed of the object using the Doppler effect. MATH TOOLS 5.2

Concept Quiz—Doppler Shift Hydrogen emits light at = 656 nm. You see a distant galaxy in which the light from hydrogen has = 696 nm. This galaxy is A. moving toward us. B. moving away from us.