Astronomy 114 Lecture 13: Energy generation, magnetic fields Martin D. Weinberg weinberg@astro.umass.edu 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, due before 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, due before Spring Break (Friday 16 March) Quizzes returned (and discussed) on Wednesday Today: Energy generation& magnetic fields OurStar,theSun,Chap.18 Properties of Stars TheNatureofStars,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 10 23 For each MeV, we get: N 1.6 10 16 = 3.1 10 7 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 10 23 For each MeV, we get: N 1.6 10 16 = 3.1 10 7 J Fusing 1 g of hydrogen (H) into helium (He) per second generates 681 mega Watts! A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 3/17
Mass, energy and fusion (2/2) Elements below iron (Fe) can from by fusion Elements below iron (Fe) cannot (radioactive decay) Most elements heavier than helium are made in stars! 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 the Chromosphere A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 9/17
Surface of the Sun Three regions: Photosphere most of Sun s luminosity Above: photons stream without interacting Below: photons interact with solar material Chromosphere Above the photosphere Corona Superheated region above the Chromosphere A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 9/17
Surface of the Sun Three regions: Photosphere most of Sun s luminosity Above: photons stream without interacting Below: photons interact with solar material Chromosphere Above the photosphere Lower density, tenuous atmosphere. Slightly cooler. Corona Superheated region above the Chromosphere A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 9/17
Surface of the Sun Three regions: Photosphere most of Sun s luminosity Above: photons stream without interacting Below: photons interact with solar material Chromosphere Above the photosphere Lower density, tenuous atmosphere. Slightly cooler. Corona Superheated region above the Chromosphere Origin of the solar wind, protons that have escaped the Sun. A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 9/17
Limb darkening Photosphere Sun appears darker around the edge Photons fromlimb from greater height in atmosphere Upper photosphere/lower chromosphere is cool (F = σt 4 ) A114: Lecture 13 05 Mar 2007 Read: Ch. 19 Astronomy 114 10/17
Limb darkening Photosphere Sun appears darker around the edge Photons fromlimb from greater height in atmosphere Upper photosphere/lower chromosphere is cool (F = σt 4 ) 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 both tension and pressure (likerubberbands) 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 both tension and pressure (likerubberbands) 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 both tension and pressure (likerubberbands) Can be strengthened by stretching them, twisting them, and folding them back on themselves. This stretching, twisting, and folding is done by the fluid 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