1 / 24

Blackbody Radiation and Spectroscopy

Blackbody Radiation and Spectroscopy. Plus … Telescopes and Imaging. Announcements. Second homework is due on Tuesday Next-week ’ s reading assignment Sections 7-1, 7-2, 7-4, 7-5, and 7-6 (pp. 146-160). Today’s topics. Origin of light Blackbody radiation Wien’s Law Stefan-Boltzman Law

Télécharger la présentation

Blackbody Radiation and Spectroscopy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Blackbody Radiation and Spectroscopy Plus … Telescopes and Imaging Telescopes and Imaging 2/1/07

  2. Announcements • Second homework is due on Tuesday • Next-week’s reading assignment • Sections 7-1, 7-2, 7-4, 7-5, and 7-6 (pp. 146-160) Telescopes and Imaging 2/1/07

  3. Today’s topics • Origin of light • Blackbody radiation • Wien’s Law • Stefan-Boltzman Law • Light as a particle • Emission and absorption spectra and Kirchoff’s Laws • Telescopes -- basics Telescopes and Imaging 2/1/07

  4. The Intensity of Light decreases with distance from the source and obeys the Inverse Square Law Telescopes and Imaging 2/1/07

  5. Origin of Light • Atomic, molecular emissions • Every atom, molecule has a characteristic spectrum (like a fingerprint) • Caused by transitions from one energy level to another • Continuum • Everything that’s heated glows • Color depends on temperature Telescopes and Imaging 2/1/07

  6. Temperature Scales • Kelvin • used by most astronomers and planetary scientists • 0 K is “absolute” zero • Kelvin  Celsius TC = TK - 273 • Celsius  Fahrenheit TF = (9/5)TC + 32 • Fahrenheit  CelsiusTC = (5/9)(TF-32) Telescopes and Imaging 2/1/07

  7. Blackbody radiation • A blackbody is a hypothetical object that is a perfect absorber of electromagnetic radiation at all wavelengths • The Sun closely approximates the behavior of blackbodies, as do other hot, dense objects • The intensities of radiation emitted at various wavelengths by a blackbody at a given temperature are shown by a blackbody curve Telescopes and Imaging 2/1/07

  8. The Sun is like a Blackbody Telescopes and Imaging 2/1/07

  9. Wien’s Law • The higher the temperature, the smaller the wavelength of maximum emission Example: A heated metal rod will start to glow red, then get brighter and glow yellow, then get brighter still and turn blue and then white Telescopes and Imaging 2/1/07

  10. Wien’s Law Wien’s law states that the dominant wavelength at which a blackbody emits electromagnetic radiation is inversely proportional to the Kelvin temperature of the object Telescopes and Imaging 2/1/07

  11. Stefan-Boltzmann Law • The Stefan-Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux Fdirectly proportional to the fourth power of the Kelvin temperature Tof the object: F= T 4 σ is called the Stefan-Boltzmann constant This law can be used to determine the temperature of the Sun, starting with a measurement of the amount of light arriving at Earth. (see Box 5-2 of the textbook) Telescopes and Imaging 2/1/07

  12. Light also behaves like a particle • Max Planck was able to derive the blackbody spectrum by assuming that light was made up of tiny, discrete packets of energy – called photons • Energy of a photon (light) with a wavelength, λ ħ = Planck’s constant = 6.625 x 10-34 J • s Telescopes and Imaging 2/1/07

  13. Photoelectric effect • When UV light strikes a metal plate, electrons are emitted by the metal and can be detected • When the plate is illuminated by visible light, no electrons are emitted. • In the light-as-a-particle picture, this can be understood ! • UV light has a shorter wavelength and a higher energy compared to visible Telescopes and Imaging 2/1/07

  14. The Modern View of Atomic Structure • Protons, Neutrons, Electrons • Size • About 10-10 m (1 Å – or 1 Angstrom) • Nucleus is only 10-14 m !! • Mass • Protons, Neutrons ~10-27 kg • Electrons ~10-31 kg • The nucleus has most of the mass, but is less than 0.03% by volume of the entire atom! Telescopes and Imaging 2/1/07

  15. What do Atoms have to do with Planetary Science? • Spectroscopy! • Emission and Absorption Lines • Each element emits/absorbs at a specific wavelength that is unique to that element • This fact can be used to infer the composition of a body or its atmosphere Telescopes and Imaging 2/1/07

  16. Kirchoff’s Laws • A hot opaque body (blackbody) produces a smooth continuous spectrum • Example: stars • A cool transparent gas in front of a source of a continuous spectrum produces an absorption-line spectrum • Example – planetary atmospheres, solar photosphere and chromosphere • A hot transparent gas radiates an emission-line spectrum (against a dark background) • Example: the solar corona Telescopes and Imaging 2/1/07

  17. Absorption lines in the Solar Spectrum Indicates the presence of Iron in the Sun Telescopes and Imaging 2/1/07

  18. Light Scattering:The reason the sky is blue (on Earth!) Telescopes and Imaging 2/1/07

  19. Look how dark it is in the shadow of the Apollo 11 lander On Earth (Tucson Barrio), we can see just fine in the shadows Telescopes and Imaging 2/1/07

  20. The “Green Flash” Telescopes and Imaging 2/1/07

  21. Telescopes and Astrophotography • Basic telescope types and how they work • Magnification and Resolution • Atmospheric Turbulence • Hubble • Adaptive Optics • Basics of Astrophotography Telescopes and Imaging 2/1/07

  22. Telescopes and Imaging 2/1/07

  23. Basic Telescope Types • Refractor • Reflector • Newtonian  • Schmidt-Cassegrain (adjacent photo) Telescopes and Imaging 2/1/07

  24. Magnification • The amount of magnification depends on the focal length of the primary and the eyepiece Telescopes and Imaging 2/1/07

More Related