Next quiz: Monday, October 24 Chp. 6 (nothing on telescopes) Chp. 7 a few problems from previous material cough, cough, gravity, cough, cough... 1
Chapter 7 Atoms and Starlight
Kirchhoff s Laws of Radiation (1) 1. A solid, liquid, or dense gas at non-zero temperature will radiate at all wavelengths and thus produce a continuous spectrum.
Kirchhoff s Laws of Radiation (2) 2. A low-density gas excited to emit light will do so at specific wavelengths and thus produce an emission spectrum. Light excites electrons in atoms to higher energy states Transition back to lower states emits light at specific frequencies
Kirchhoff s Laws of Radiation (3) 3. If light comprising a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum. Light excites electrons in atoms to higher energy states Frequencies corresponding to the transition energies are absorbed from the continuous spectrum.
The Spectra of Stars
The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum.
The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at specific frequencies.
The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at specific frequencies. => Spectra of stars are absorption spectra.
Emission and Absorption lines are produced when interact with. a) protons, electrons b) neutrons, protons c) neutrons, photons d) electrons, photons 7
An incandescent bulb, fluorescent light, and the Sun emit,, and spectra, respectively. a) b) c) d) e) Continuous, emission, absorption Continuous, absorption, emission Continuous, continuous, continuous Absorption, emission, continuous Absorption, emission, absoprtion 8
1 2 3 4 Which transitions were responsible for each of these absorption lines? a) A: 1-2 B: 2-4 C: 1-4 b) A: 1-4 B: 2-4 C: 1-2 c) A: 4-1 B: 4-2 C: 2-1 23
The Doppler Effect 10
Two stars orbiting one another. The diagram shows the orbital motion of one of the stars, and four different positions are marked (A, B, C, D). At which position is the light from the star redshifted? blueshifted? not shifted at all? D a) A, C, B/D b) C, A, B/D c) B, D, A/C d) D, B, A/C A C B 11
The Sun as a Star (Chp. 8) 12
The Sun produces its energy from a) Electric currents generated in its core b) Chemical reactions (oxidation reactions) producing flames c) Fusion of hydrogen into helium d) Disintegration of helium into hydrogen 13
A Garden Variety Star Distance: 1.5 10 11 meters Mass: 2 10 30 kg Size: 7 10 8 meters Surface Temperature: 5800 K Gaseous! Made of: 92% Hydrogen 7.8% Helium 0.2% other Radar Measurements Laws of Gravity Angular Size Wien s Law Pressure/Temperature Spectroscopy 14
Photosphere: where most of the photons escape the Sun. Approximately 500 km thick (small compared to radius!) 15
The Sun at different wavelengths Unfiltered light; optical; sunspots; photosphere 16
Filtered optical (hydrogen emission); plages; chromosphere 17
Ultra-violet emission; coronal holes, prominences; corona 18
X-Ray emission; coronal holes, prominences; corona 19
Sun Spots Cooler regions of the photosphere (T 4240 K) Only appear dark against the bright sun; would still be brighter than the full moon when placed on the night sky!
Zeeman Effect 21
Zeeman Effect 21
The Magnetic Field of the Sun Current loop Bar Magnet Rotating Plasma 22
Zeeman effect reveals magnetic nature of active regions. Observations reveal switching polarity 23
Active Regions Visible Ultraviolet
Magnetic fields loop through the surface of the Sun like fibers in a carpet. Charged particles are accelerated by the magnetic force 25
Close-up view of sunspot taken by TRACE satellite. 26
Sunspots at base of prominence 27