ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies � NNOUNCEMENTS FIRST MIDTERM NEXT THURSDAY FIRST MIDTERM NEXT THURSDAY � irst homework on mas � ring as � onom � due � day by 5p � � econd homework on mas � ring as � onom � available � om � day 11am, and due on TUESDAY, 09/22, by 5pm.
On to Our Nearest Star Chap 14 Chap 14 On to Our Nearest Star
De-Mystifying science De-Mystifying science The case of the Sun The case of the Sun • Ancient philosophers/scientists thought that the sun was some kind of fire. • What things would we want to ask about the Sun in this course?
1. How far is the Sun? 2. What is the Sun made of? 3. How does the Sun produce its energy? 4. How old is the Sun? 5. Why is the Sun stable? 6. What’s inside the Sun? 7. What will be the end of the Sun? 8. How massive is the Sun?
1. How far is the Sun? 1. How far is the Sun? • How can we determine the distance of the Sun? 1. Find the distance to an inner planet in Astronomical Astronomical Units (AU). Units (AU). 2. Find distance to distance to Sun at position of Sun at position of greatest elongation greatest elongation � � a � =152 � i � ion k � - � � i � =146 � i � ion k �
2. What is the Sun made of? 2. What is the Sun made of? • How can we determine the composition of the Sun?
Absorption Line Spectra Absorption Line Spectra
3. How does the Sun produce 3. How does the Sun produce its energy? its energy? 4. How old is the Sun? 4. How old is the Sun?
Could it be chemical burning? Could it be chemical burning? 1. Energy released by burning oil ~10 7 joules/kg 2. Solar energy output (Luminosity) = 3 x 10 26 joules/sec (mostly in visible light.) 3. Need (3 x 10 26 joules/sec) / (10 7 joules/kg) = 3 x 10 19 kg of burning oil per second 4. How long will the Sun last? � M Sun /(amount burning per second) = (2 x 10 30 kg)/ 3 x 10 19 kg/s = 6.6 x 10 10 seconds = 2,000 2,000 years!! years!!
Maybe it’ ’s gravitational s gravitational Maybe it contraction? contraction? • Gravitational contraction (Kelvin-Helmholtz contraction) can give ~10,000 times more energy than chemical burning. How old can the Sun be if its source of energy is gravitational contraction? ~25,000,000 years. ~25,000,000 years. But geological record showed age > 150,000,000 years!
Energy generated by FUSION! FUSION! Energy generated by � =mc 2 Proton-Proton chain � =mc 2
Fusion NOT NOT fission fission as as energy source energy source Fusion Fission Fission Fusion Fusion Big nucleus splits into Small nuclei stick together smaller pieces to make a bigger one (Nuclear power plants) (Sun, stars)
Sun’ ’s energy budget s energy budget Sun • Helium has atomic mass 3.97 times that of Helium has atomic mass 3.97 times that of • hydrogen, NOT exactly 4 times hydrogen, NOT exactly 4 times • Tiny amount of the protons Tiny amount of the protons’ ’ mass is lost to mass is lost to • energy energy 2 (a little mass makes a lot of energy!) E = mc 2 • E = mc (a little mass makes a lot of energy!) • • 600 million tons of H every second is converted 600 million tons of H every second is converted • to 596 million tons of He… …4 million tons of mass 4 million tons of mass to 596 million tons of He are converted into energy each second! are converted into energy each second!
Need high temperatures to make Need high temperatures to make fusion happen fusion happen High temperature High temperature gives high speeds gives high speeds
Clicker Question Clicker Question The Sun is made up of (mostly) The Sun is made up of (mostly) hydrogen. Yet the P-P chain starts P-P chain starts hydrogen. Yet the with two protons. Why are they not with two protons. Why are they not with their electrons? with their electrons? A. The material is a plasma so the nuclei and electrons are all free. B. The electrons have all moved to the outer layers of the Sun. C. The Sun is electrically positive (thus the magnetic fields) so all that exists are hydrogen ions. D. Neutral hydrogen only consists of one proton and one neutron in the first place. E. The electrons have been all annihilated with positrons.
Clicker Question Clicker Question The Sun is made up of (mostly) The Sun is made up of (mostly) hydrogen. Yet the P-P chain starts P-P chain starts hydrogen. Yet the with two protons. Why are they not with two protons. Why are they not with their electrons? with their electrons? A. The material is a plasma so the nuclei and electrons are all free. B. The electrons have all moved to the outer layers of the Sun. C. The Sun is electrically positive (thus the magnetic fields) so all that exists are hydrogen ions. D. Neutral hydrogen only consists of one proton and one neutron in the first place. E. The electrons have been all annihilated with positrons.
Do we have direct evidence for Do we have direct evidence for fusion in the Sun? fusion in the Sun? • YES! Neutrinos
Those Mysterious Neutrinos Those Mysterious Neutrinos MADE BY HYDROGEN FUSION IN CORE HYDROGEN FUSION IN CORE MADE BY • Mass-less or (likely) with very small Mass-less or (likely) with very small • masses, travel close to speed of light travel close to speed of light masses, • Don Don’ ’t interact (almost) with other matter: t interact (almost) with other matter: • requires lead wall 1 light year thick to stop requires lead wall 1 light year thick to stop a neutrino! a neutrino! 38 neutrinos/sec from the 10 38 • Lots of them: Lots of them: 10 neutrinos/sec from the • 15 coming through YOU each sec Sun, 10 15 coming through YOU each sec ! ! Sun, 10 • But we can still catch some, using massive But we can still catch some, using massive • underground “ “detectors detectors” ”: : BIG PUZZLE BIG PUZZLE underground
Big Puzzle: First Neutrino Detector Big Puzzle: First Neutrino Detector • Located deep underground, • Located deep underground, ground blocked other ground blocked other particles particles • Huge underground vat of • Huge underground vat of dry-cleaning fluid (chlorine) dry-cleaning fluid (chlorine) – Chlorine captures neutrino, Chlorine captures neutrino, – becomes radioactive argon becomes radioactive argon • Only collects 1 neutrino • Only collects 1 neutrino about every 3 days -- even -- even about every 3 days with 100,000 gallons with 100,000 gallons • Solar theory predicted • Solar theory predicted THREE TIMES more! more! THREE TIMES • Big hunt started, called • Big hunt started, called SOLAR NEUTRINO SOLAR NEUTRINO PROBLEM PROBLEM Homestake Gold Mine, South Dakota Homestake Gold Mine, South Dakota
Sudbury Neutrino Observatory (SNO) Sudbury Neutrino Observatory (SNO) • Uses Uses “ “heavy water heavy water” ” -- -- • some H in H 2 0 replaced some H in H 2 0 replaced by its stable isotope by its stable isotope deuterium (P+N) deuterium (P+N) • SNO captures SNO captures all three all three • types of neutrinos types of neutrinos (electron, muon muon, , tao tao) ) (electron, – Detects the Detects the RIGHT RIGHT – numbers!! numbers!! • “ “Solar neutrino problem Solar neutrino problem” ” • leads to big physics leads to big physics advance (2002 Nobel Prize; advance (2002 Nobel Prize; Davis & Koshiba Koshiba) ) Davis &
Clicker Question Clicker Question Could the neutrinos flowing through Could the neutrinos flowing through our bodies be a cause of cancer or our bodies be a cause of cancer or other cellular damage? other cellular damage? A. YES YES, because there are so many and , because there are so many and A. they carry a lot of energy they carry a lot of energy B. NO NO, because they don , because they don’ ’t interact with t interact with B. anything and just flow through anything and just flow through C. MAYBE MAYBE, it depends on if they are , it depends on if they are C. electron, muon muon or or tau tau neutrinos. neutrinos. electron,
Clicker Question Clicker Question Could the neutrinos flowing through Could the neutrinos flowing through our bodies be a cause of cancer or our bodies be a cause of cancer or other cellular damage? other cellular damage? A. YES YES, because there are so many and , because there are so many and A. they carry a lot of energy they carry a lot of energy B. NO NO, because they don , because they don’ ’t interact with t interact with B. anything and just flow through anything and just flow through C. MAYBE MAYBE, it depends on if they are , it depends on if they are C. electron, muon muon or or tau tau neutrinos. neutrinos. electron,
Clicker Question Clicker Question How does the number of neutrinos How does the number of neutrinos passing through your body at night passing through your body at night compare with the number passing compare with the number passing through during the day? through during the day? A. About the same. About the same. A. B. Much smaller during the night. Much smaller during the night. B. C. Much larger during the night. Much larger during the night. C. D. Neutrinos don Neutrinos don’ ’t pass through our t pass through our body. body. D.
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