Astronomy 114 - University of Massachusetts Amherstweinberg/a114/lectures/... · 2007. 3. 5. ·...
Transcript of Astronomy 114 - University of Massachusetts Amherstweinberg/a114/lectures/... · 2007. 3. 5. ·...
Astronomy 114
Lecture 13: Energy generation, magnetic fields
Martin D. Weinberg
UMass/Astronomy Department
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—1/17
Announcements
PS #4 will be posted on Wednesday or Friday, duebefore Spring Break (Friday 16 March)
Quizzes returned (and discussed) on Wednesday
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—2/17
Announcements
PS #4 will be posted on Wednesday or Friday, duebefore Spring Break (Friday 16 March)
Quizzes returned (and discussed) on Wednesday
Today:
Energy generation & magnetic fields
Our Star, the Sun, Chap. 18
Properties of Stars
The Nature of Stars, Chap. 19
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—2/17
Mass, energy and fusion (1/2)
Mass deficit: 0.03035 u
E = 0.03035 u × 931.494 MeV/u = 28.27 MeV
Or: 7.07 MeV per nucleon
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—3/17
Mass, energy and fusion (1/2)
Mass deficit: 0.03035 u
E = 0.03035 u × 931.494 MeV/u = 28.27 MeV
Or: 7.07 MeV per nucleon
How many H atoms in one gram?
Avogadro’s number: N = 6.02 × 1023
For each MeV, we get: N × 1.6 × 10−16
= 3.1 × 107 J
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—3/17
Mass, energy and fusion (1/2)
Mass deficit: 0.03035 u
E = 0.03035 u × 931.494 MeV/u = 28.27 MeV
Or: 7.07 MeV per nucleon
How many H atoms in one gram?
Avogadro’s number: N = 6.02 × 1023
For each MeV, we get: N × 1.6 × 10−16
= 3.1 × 107 J
Fusing 1 g of hydrogen (H) into helium (He) persecond generates 681 mega Watts!
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—3/17
Mass, energy and fusion (2/2)
Elements belowiron (Fe) can fromby fusion
Elements belowiron (Fe) cannot(radioactive decay)
Most elements heavier than helium are made instars!
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—4/17
P-P fusion reaction
3 steps in a fusion reaction
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—5/17
P-P fusion reaction
3 steps in a fusion reaction
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—5/17
P-P fusion reaction
3 steps in a fusion reaction
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—5/17
Solar model (1/2)
Fusion: radii < 0.25R⊙
Radiative diffusion:0.25R⊙ < radii < 0.71R⊙
Convection:0.71R⊙ < radii < 1.00R⊙
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—6/17
Solar model (2/2)
Theoretical computer models
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—7/17
Solar model (2/2)
Theoretical computer models
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—7/17
Testing the theory
Neutrinos
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—8/17
Testing the theory
Neutrinos
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—8/17
Testing the theory
Neutrinos
Helioseismology
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—8/17
Surface of the Sun
Three regions:
Photosphere— most of Sun’s luminosity
Chromosphere— Above the photosphere
Corona— Superheated region above theChromosphere
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—9/17
Surface of the Sun
Three regions:
Photosphere— most of Sun’s luminosityAbove: photons stream without interacting
Below: photons interact with solar material
Chromosphere— Above the photosphere
Corona— Superheated region above theChromosphere
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—9/17
Surface of the Sun
Three regions:
Photosphere— most of Sun’s luminosityAbove: photons stream without interacting
Below: photons interact with solar material
Chromosphere— Above the photosphereLower density, tenuous “atmosphere”. Slightlycooler.
Corona— Superheated region above theChromosphere
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—9/17
Surface of the Sun
Three regions:
Photosphere— most of Sun’s luminosityAbove: photons stream without interacting
Below: photons interact with solar material
Chromosphere— Above the photosphereLower density, tenuous “atmosphere”. Slightlycooler.
Corona— Superheated region above theChromosphereOrigin of the solar wind, protons that have escaped theSun.
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—9/17
Limb darkening
Photosphere–Sun appears darker around the edge
Photons from limb from greater height in atmosphere
Upper photosphere/lower chromosphere is cool
(F = σT4)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—10/17
Limb darkening
Photosphere–Sun appears darker around the edge
Photons from limb from greater height in atmosphere
Upper photosphere/lower chromosphere is cool
(F = σT4)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—10/17
Corona
Image of Sun during total eclipse
Material streams away from Sun
Narrow transition between chromosphere and corona
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—11/17
Sunspots (1/2)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—12/17
Sunspots (1/2)
[movie]
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—12/17
Sunspots (2/2)
Sunspots are regions of high magnetic field
Zeeman splitting
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—13/17
Consequences: magnetic fields!
Generated by moving charges: electric currents
Continuous loops of lines of force that have bothtension and pressure (like rubber bands)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—14/17
Consequences: magnetic fields!
Generated by moving charges: electric currents
Continuous loops of lines of force that have bothtension and pressure (like rubber bands)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—14/17
Consequences: magnetic fields!
Generated by moving charges: electric currents
Continuous loops of lines of force that have bothtension and pressure (like rubber bands)
Can be strengthened by stretching them, twistingthem, and folding them back on themselves.
This stretching, twisting, and folding is done by thefluid flows within the Sun!
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—14/17
Solar dynamo (1/2)
Magnetic field is trapped in ionized gas (plasma)
Rotating Sun winds up the field lines
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—15/17
Solar dynamo (1/2)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—16/17
Solar dynamo (1/2)
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—16/17
Solar dynamo (2/2)
TRACE solar
mission
(NASA)
UV image
A114: Lecture 13—05 Mar 2007 Read: Ch. 19 Astronomy 114—17/17