CH9 - Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson & McMillan, Astronomy Chapter 9 The Sun The Sun The The Sun is an average star The The Sun is the closest star – most of our detailed most understanding of stars comes from the sun comes The Sun: Comparisons (chap 10) The The Sun vs. Earth The Sun Radius 100 Mass 300,000 Density 1.4 g/ml Rotation 24.9-29.8 days Surface Temperature 5500 C (5780 K) Earth 1 1 5.5 g/ml 1 day 17 C (290 K) The Sun: Close-up study The We can make out surface details on the Sun Sun Visible Appearance: Visible Yellow Yellow Sharp-edge (Why?) Sharp Dark Spots Dark Visible Light Image Structure of the Sun Structure Entirely hot gas No solid surface No Apparent surface is a thin layer called the Photosphere Photosphere The photosphere is where the visible light comes from – thin edge Structure of the Sun Structure Key Inner Zones: Key Core Core Radiation Zone Radiation Convection Zone Convection Key Outer Zones: Key Photosphere Photosphere Chromosphere Chromosphere Corona Corona Luminosity of the Sun Luminosity The Solar Luminosity is the total The light output from the Sun light Solar Constant (at 1 AU): F = 1400 Watts per m2 1400 Spread over the 1 A.U. sphere: sphere: Total Solar Luminosity: Total L = 4x1026 Watts 4x10 L F= 2 4π r The Luminosity of the Sun The Why does the Sun shine? The heat leaving the Sun’s surface is the The surface same as the heat generated in the centre same The heat in the centre is generated by nuclear fusion reactions (more later…) nuclear Solar Interior Solar How do we know what How the Sun is like inside? the Helioseismology Helioseismology Mathematical Models Mathematical Solar Interior Solar Helioseismology: Study of vibration of the surface of the Sun (using the Doppler effect) Sun Like Earth based seismology – waves waves travelling through the Sun indicate interior structure interior Solar Interior Solar Mathematical models: 1. The Sun must hold itself up against gravity: itself High Pressure in the High centre centre Solar Interior Solar Mathematical models: 2. The Sun must be hot enough to allow nuclear reactions at the centre: reactions 15 Million K temperature in 15 the core core Solar Interior Solar Mathematical models: 3. There must be mechanisms to move heat from the core to the surface heat Radiation: Light directed outwards Convection: Moving hot gas around Convection: Solar Interior Solar The Standard Model There is a widely accepted mathematical model that fits the observations well observations This model gives the standard picture of solar structure of Energy Transport: Energy Radiation vs. Convection Where gas is very hot it is transparent Where and radiation carries heat effectively and Where gas is more opaque, light cannot Where travel far without being absorbed travel Energy Transport: Energy Radiation vs. Convection When radiation can’t travel heat builds until travel the gas moves (like a boiling pot) the Gas motions carrying heat is Convection Gas Convection Solar Convection Solar Fine detail due to Fine convection is visible on the Sun’s surface: the surface: Granulation Granulation Hotter newly risen gas bubbles are brighter bubbles Colder falling gas bubbles are darker bubbles The Solar The Atmosphere The Sun is almost like a black-body radiating at black body 5800 K 5800 We see an absorption spectrum – the lines tells the us what elements are present present Absorption Spectrum Of the Sun The Solar Composition The The Sun is mostly Hydrogen 71 % The Helium 27 % Helium Oxygen, Carbon, Nitrogen, Silicon, Iron, etc… 2% etc Fusion reactions in the core are very very slowly changing Hydrogen into Helium Chromosphere Chromosphere The Chromosphere iis a faint layer of Chromosphere s gas on top of the photosphere gas It is only visible when the brighter photosphere is blocked photosphere The Corona The Beyond the chromosphere chromosphere the solar atmosphere is the very thin and very hot: very The Corona The Corona is at 1 Million K and emits X-rays and Corona to Solar Wind Corona The Corona is so hot the gas can escape the Sun’s gravity escape This gas flows away as the Solar Wind This Only 0.1 % of the Sun mass has been lost as Solar Wind in 5 Billion years lost The Active Sun Active The Sun in X-rays The Corona and Solar Wind are not steady not Magnetic activity on the surface of the Sun dramatically changes the structure of the Corona and the intensity of the Solar Wind Solar The Active Sun: Sunspots The Sunspots Sunspots Sunspots are colder places where magnetic fields stop convection magnetic They occur in pairs at the N and S end of magnetic field bundles end Solar Magnetism Solar The Sun has a very strong Magnetic field field Solar dynamo: Strong convection and rotation produce the magnetic field the This is not a static situation – the the magnetic field is continually changed magnetic Solar Magnetism Solar Sunspots and Sunspots Magnetism When the Solar Magnetic field is strong it pushes out of the solar surface: of Sunspots Sunspots only occur when the field is strong the The Solar Cycle The The Sun’s Magnetic Field gets The Magnetic strongest every 11 years strongest The N/S Magnetic poles then flip The The total Solar Cycle is 22 years The The Solar Cycle: Sunspot Numbers Sunspot Solar Activity Solar When the field is strong prominences (loops) and Solar flares occur Solar Bursts of Solar Wind associated with flares can take out satellites take Mid term Mid 7-8 pm today Building T29 (near stadium) Building Family Name: A-J room 101 K-Z room 105 The Sun’s Core: Heat source The The Sun’s core is hot enough to allow core nuclear fusion nuclear Atomic nuclei are positively charged Atomic Positive charges repel You need very fast moving nuclei to get close enough for fusion close Nuclear Fusion Nuclear Very close atomic nuclei attract! Very Light nuclei release energy when they fuse to make heavier ones fuse The new heavier nuclei weigh less! The E=mc2 The difference is available as heat and gamma rays gamma Fusion is more fuel efficient than anything on Earth on Aside: Aside: Fusion on Earth? Scientist have been trying to achieve fusion on Earth fusion Super hot gas is contained with strong magnetic fields fields Still marginal The Proton-Proton Chain The Fusion in the Sun Fusion The Sun predominantly uses the proton-proton chain of fusion reactions proton The net effect: The 4 Hydrogens convert to 1 Helium (lighter) Hydrogens Lots of energy is released Lots 2 Neutrinos are released Neutrinos Solar Neutrinos Solar Neutrinos are particles that interact with almost nothing! almost They leave the sun immediately after they are formed they They get to Earth in around 8 minutes – traveling close to the speed of light Only 1/3 the expected number are seen! seen! The Solar Neutrino Problem The 1/3 The expected solar neutrinos are seen 1/3 The light/heat associated with the reactions gets out much later reactions Explanations: 1. The Sun is suddenly burning at 1/3 the The normal rate -OR2. Neutrinos are funkier than we suspected SNO: The Sudbury Neutrino Observatory Neutrino In Sudbury, Canada in a deep mine there is an experiment to detect neutrinos neutrinos There are 3 experiments globally globally The latest results from SNO indicate solar neutrinos are spread among 3 types spread ...
View Full Document

This note was uploaded on 04/10/2011 for the course ASTRONOMY 1f03 taught by Professor Wadsley during the Spring '11 term at McMaster University.

Ask a homework question - tutors are online