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Astronomy 1020-H Stellar Astronomy Spring_2014 Day-11

Astronomy 1020-H Stellar Astronomy Spring_2014 Day-11. Lecture Tutorial EM Spectrum : (pg. 47). 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 !!!!

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Astronomy 1020-H Stellar Astronomy Spring_2014 Day-11

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  1. Astronomy 1020-H Stellar Astronomy Spring_2014 Day-11

  2. Lecture Tutorial EM Spectrum: (pg. 47) • 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.

  3. Exam Sadistics Metric Ex-1 Number 17 Mean 75.1 StdDev 12.1 Median 74 Mode 70 High 92 Low 51

  4. Course Announcements • Smartworks Chapters 5: Due Mon. 2/17

  5. Almost all knowledge of the universe beyond Earth comes from light. • Light can tell us about objects in space: temperature, composition, speeds, and more.

  6. What Light Can Tell Us. • Photometry – Study of Brightness: • Luminosity, Est. of Distance, Rough Temp. of Star • Spectroscopy – Study of the EM Spectrum: • Composition, Radial Velocity, Temp., Surface-gravity • Mass for compact objects • Astrometry – Study of Positions: • Tangential Motion, Distance • Polarimetry – Study of Polarization of Light: • Magnetic Field

  7. Light moves at 300,000 km/s in a vacuum. • First measured by Rømer when observing Jupiter’s moons. • Speed is slower in other materials, e.g., glass.

  8. Light is a wave of combined electricity and magnetism, called an electromagneticwave. • Changing electric and magnetic fields create a self-sustaining electromagnetic wave.

  9. Wavelength (): length between crests. • Amplitude: height. • Frequency (f): number of waves that pass by each second. • Period (P): time to complete one cycle.

  10. A long wavelength means low frequency. • A short wavelength means high frequency. • The speed of light, c,is constant.

  11. MATH TOOLS 5.1 • 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:

  12. Visible spectrum: small range of wavelengths that humans can see. • Red light = longest wavelength ( ~ 750 nm). • Violet light = shortest wavelength ( ~ 380 nm). • “Roy G. Biv.”

  13. Visible light is just one small part of the electromagnetic spectrum: Gamma rays X-rays UV Visible IR Microwave Radio  increasing f decreasing

  14. 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.

  15. Concept Quiz—AM and FM On the FM dial, the frequencies run from 88 to 107 MHz (million cycles per second). On the AM dial, the range is 570 to 1600 kHz (thousand cycles per second). Which statements are true? • FM photons have shorter wavelengths than AM. • FM photons have higher energies than AM. • FM photons travel at the same speed as AM. • All the above statements are true.

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

  17. 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.

  18. 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.

  19. 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.

  20. B:  = ? A:  = 450 nm 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? • 225 nm • 450 nm • 900 nm

  21. 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.

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