Astronomy 1010 Planetary Astronomy Fall_2015 Day-18

Exam Sadistics Ex-1Ex-2 N7072 Ave Stdev Median Mode4961 High9194 Low3123

Course Announcements Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at 7:30pm – at the Observatory. Exam-2 will be Friday, Oct. 9; Ch. 3, 4, & 5 SW-chapter 4 posted: due Today SW-chapter 5 posted: due Fri. Oct. 9

Definitions & Terms -1 Excitation: The process of an electron absorbing a photon, gaining energy. De-Excitation : The process of an electron losing a photon, losing energy. Ionization: The process of an atom losing an electron due to absorbing too much energy. Recombination : The process of an atom capturing an electron as it loses energy.

Lab This Week The Spectrometer

Lab This Week The Spectrometer

Photons  Light also behaves as a particle.  Photon: particle of light.  Photons carry energy and can have different amounts of energy.  Photons with high energy = light with high frequency.  Photons with low energy = light with low frequency.  Atoms can absorb or emit photons.

 Atoms have a dense nucleus of protons and neutrons.  Electrons surround the nucleus in a “cloud.”

 Electrons can have certain energies; other energies are not allowed.  Each type of atom has a unique set of energies.  Energy level diagram represents this.  Lowest energy is the ground state.

 Emission: An electron emits a photon and drops to a lower energy state, losing energy.  The photon’s energy is equal to the energy difference between the two levels.

 Absorption: An electron absorbs the energy of a photon, moving the electron to a higher energy level.  The photon’s energy has to be equal to the energy difference between the two levels.

 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.

i_Clicker Question Light & Spectra: Electron Transitions Light & Spectra: Permitted Electron Orbits #1

 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