next quiz: monday, october 24 chp. 6 (nothing on ... next quiz: monday, october 24 chp. 6 (nothing...

1

Next quiz: Monday, October 24Chp. 6 (nothing on telescopes)Chp. 7a few problems from previous material

cough, cough, gravity, cough, cough....

Monday, October 24, 2011

Atoms and StarlightChapter 7


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 StarsThe inner, dense layers of a star produce a continuous

(blackbody) spectrum.




Cooler surface layers absorb light at specific frequencies.




Cooler surface layers absorb light at specific frequencies.

=> Spectra of stars are absorption spectra.


7

Emission and Absorption lines are produced when _____ interact with _____. a) protons, electrons b) neutrons, protons c) neutrons, photons d) electrons, photons


8

An incandescent bulb, fluorescent light, and the Sun emit ________, ________, and _________ spectra, respectively.

a) Continuous, emission, absorptionb) Continuous, absorption, emissionc) Continuous, continuous, continuousd) Absorption, emission, continuouse) Absorption, emission, absoprtion


23

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


10

The Doppler Effect


11

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? a) A, C, B/D b) C, A, B/D c) B, D, A/C d) D, B, A/C

B

D

CA


12

The Sun as a Star (Chp. 8)


13

The Sun produces its energy froma) Electric currents generated in its coreb) Chemical reactions (oxidation reactions)

producing flamesc) Fusion of hydrogen into heliumd) Disintegration of helium into hydrogen


14

A Garden Variety Star• Distance: 1.5 × 1011 meters

• Mass: 2 × 1030 kg

• Size: 7 × 108 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


15

Photosphere: where most of the photons escape the Sun.

Approximately 500 km thick (small compared to radius!)


16

Unfiltered light; optical; sunspots; photosphere

The Sun at different wavelengths


17

Filtered optical (hydrogen emission); plages; chromosphere


18

Ultra-violet emission; coronal holes, prominences; corona


19

X-Ray emission; coronal holes, prominences; corona


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!


21

Zeeman Effect


22

The Magnetic Field of the Sun

Current loopBar Magnet

Rotating PlasmaMonday, October 24, 2011

23

Observations reveal switching polarity

Zeeman effect reveals magnetic nature of active regions.


Active Regions

Visible

Ultraviolet


25

Magnetic fields loop through the surface of the Sun like fibers in a carpet.

Charged particles are accelerated by the magnetic force.


26

Close-up view of sunspot taken by TRACE satellite.


27Sunspots at base of prominence


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