AST 115 1st Edition Lecture 11 Outline of Last Lecture I. Particle Nature of Light continueda. DispersionII. The Doppler EffectIII. Properties or Powers of a Telescopea. Magnificationb. Light-gathering powerc. Resolving powerIV. Telescopes and ObservatoriesOutline of Current Lecture I. Reflecting Telescopes ContinuedII. Astronomical Detection EquipmentIII. Radio AstronomyIV. Other AstronomiesV. Why stars have colorsa. Luminous objectsb. Non-luminous objectsVI. Radiation Lawsa. Blackbody radiationb. Planck/Radiation Curvec. Stefan-Boltzmann Lawd. Wien’s LawVII. Kirchhoff’s Laws of SpectroscopyVIII. Bohr’s Model of the Hydrogen AtomCurrent Lecture Reflecting telescopes continued:o The Baker Observatory These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- 16” Cassegrain Reflector [in the large dome]- 14” Celestron Schmidt-Cassegrain hybrid (mirror + lens) [in the small dome]- Baker Observatory Robotic Autonomous Telescope = BORATo Multiple-Mirror Telescopes- The Keck 10-meter Twinso Thin, large diameter Mirrors- An 8.4 meter mirror for the LBT Astronomical Detection Equipmento Photography (film)- Astronomers didn’t bother to make positive prints; they just used the negativeso Spectroscopyo Photometry = to measure the brightness of a staro CCD Detectors (Charge-Coupled Devise)- Very sensitive (shows more stars; more detection of stars compared to film photographs) Radio Astronomyo Radio observatories- NRAO 100-meter (National Radio Astronomy Observatory)o Radio Interferometry = operating two or more radio dishes at the same time- Very Large Array = VLA (New Mexico) Other Astronomieso Why do astronomers have telescopes placed into orbit?- Astronomers have telescopes placed into orbit in order to access wavelengths of radiation that don’t pass through the atmosphere. Infrared Ultraviolet- Even optical telescopes work better in orbit Hubble Space Telescope Why do stars have color?o Stars have color because they are luminous objects.o Luminous objects:- If the temperature of an object is high enough, some of the energy that it radiates is in the visible part of the spectrum and it is self-luminous.- What determines color of a luminous object? Reflected light is insignificant compared to the radiated light. Experiments in the 19th century have shown that the nature of theradiation from a luminous object depends only on the temperature of the object.- Examples of a luminous object = the Sun, the stars, comets…o Non-luminous objects:- The color of a non-luminous object is determined by the wavelengths of light that it reflects.- In addition to the reflected light, the object will also absorb a portion of the incident light energy.- The object must also re-radiate a portion of that absorbed energy or else it will become infinitely hot. This is normally radiated at infrared wavelengths.- Examples of non-luminous objects: a tree, a rock, people, Earth, metals, mirrors… Radiation Lawso Blackbody = ideal radiator- Absorbs 100% of incident radiation- Reflects 0% of incident radiation- Re-radiates 100% of incident radiationo Planck or Radiation Curve- Graph showing amount (intensity) of radiation plotted against wavelengthor color.o Stefan-Boltzmann Law:- “The amount of radiation emitted per square meter of a surface by a blackbody depends on the 4th power of temperature.” (This is important in the determination of the true brightness of an object)o Wien’s Law:- “The wavelength of the peak of a Planck curve depends inversely on the temperature.” (Peak shifts toward shorter wavelengths for hotter blackbodies). This explains why stars have colors. Kirchhoff’s Laws of Spectroscopy:o Continuous Spectrum – all colors of the rainbow are present. The light source is hot and dense.o Emission (Bright Line) Spectrum – only certain colors are present. The light source is hot and has low density.o Absorption (Dark Line) Spectrum – only certain colors are missing. The light source is hot and dense surrounded by not as hot and low density. Bohr’s Model of the Hydrogen Atomo The hydrogen atom consists of a single positive (+) proton as the nucleus with one negative (-) electron in orbit around it.o The electron can only be in one of the certain circular orbits. The farther the orbit is from the proton, the more energy the electron has.o The spacing between orbits corresponds to a precise energy difference. When the electron makes a transition between orbits, a specific energy is given to or taken from the electron.o The energy difference corresponds to the energy, and thus wavelength, of the proton
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