1. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Plus … Telescopes and Imaging Blackbody Radiation and Spectroscopy

2. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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)

3. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

4. PTYS/ASTR 206Telescopes and Imaging 2/1/07 The Intensity of Light decreases with distance from the source and obeys the Inverse Square Law

5. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Origin of Light Continuum –Everything that’s heated glows –Color depends on temperature Atomic, molecular emissions –Every atom, molecule has a characteristic spectrum (like a fingerprint) –Caused by transitions from one energy level to another

6. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Temperature Scales Kelvin –used by most astronomers and planetary scientists –0 K is “absolute” zero Kelvin  Celsius T C = T K - 273 Celsius  Fahrenheit T F = (9/5)T C + 32 Fahrenheit  Celsius T C = (5/9)(T F -32)

7. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

8. PTYS/ASTR 206Telescopes and Imaging 2/1/07 The Sun is like a Blackbody

9. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

10. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

11. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Stefan-Boltzmann Law The Stefan-Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux F directly proportional to the fourth power of the Kelvin temperature T of 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)

12. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

13. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

14. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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!

15. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

16. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

17. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Absorption lines in the Solar Spectrum Indicates the presence of Iron in the Sun

18. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Light Scattering: The reason the sky is blue (on Earth!)

19. PTYS/ASTR 206Telescopes and Imaging 2/1/07 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

20. PTYS/ASTR 206Telescopes and Imaging 2/1/07 The “Green Flash”

21. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Telescopes and Astrophotography Basic telescope types and how they work Magnification and Resolution Atmospheric Turbulence –Hubble –Adaptive Optics Basics of Astrophotography

22. PTYS/ASTR 206Telescopes and Imaging 2/1/07

23. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Basic Telescope Types Refractor  Reflector –Newtonian  –Schmidt- Cassegrain (adjacent photo)

24. PTYS/ASTR 206Telescopes and Imaging 2/1/07 Magnification The amount of magnification depends on the focal length of the primary and the eyepiece