3/26/2018. The Sun. Phys1403 Introductory Astronomy. Topics in Chapter 8 that we will cover. Topics in Chapter 8 that we will cover.

Transcription

1 Foundations of Astronomy 13e Seeds Phys1403 Introductory Astronomy Instructor: Dr. Goderya Chapter 8 The Sun Topics in Chapter 8 that we will cover General Properties Solar Atmosphere and Surface Temperature variation Solar Interior Energy Flow Methods of Energy Flow Density Pressure Topics in Chapter 8 that we will cover Energy Productions Nuclear Fission Nuclear Fusion Comparing Fusion with Burning Coal Hydrostatic Equilibrium Gravity Gas Pressure The Sun s Future (Briefly) The remaining topics: Read it on your own. The Sun Is Just a Normal Star Observing the Sun Warning! Never look directly at the sun through a telescope or binoculars! Use a projection technique or a special sun viewing filter A Giant Ball of Gas on Fire 1

2 General Properties Average star Spectral type G2 Only appears so bright because it is so close. Absolute visual magnitude = 4.83 (magnitude if it were at a distance of 32.6 light years) 109 times Earth s diameter 333,000 times Earth s mass Consists entirely of gas (av. density = 1.4 g/cm 3 ) Central temperature = 15 million 0 K Surface temperature = K ClassAction: Cengage Astronomy Learning 2016 Education at the University of Nebraska-Lincoln Web Site ( Solar Interior: Core and Envelope Gravity Pulls Matter Inward Core Envelope This where almost all the energy is generated What Keeps the Sun from Collapsing on itself? KCVS Gas Pressure Pushes Outwards Density Matters in the Sun Density =Mass/Volume Where Does Pressure Come From? Indiana.edu 2

3 Gas Pressure: Ideal Gas Law Pressure = (density)(temperature)(constant) Gas Pressure is the force of the gas particles colliding with the walls of its container Density and Temperature control the amount of pressure Energy in the Sun Where does the Sun gets its energy from? Coal? Chemical Burning? Nuclear Fission? Or Nuclear Fusion? Comparing Oil, Coal and Fusion Nuclear Fusion is more Efficient Comparing The Sun with a Nuclear Bomb Total Output Power 4 x watts 100 billion 1 megaton nuclear bombs per second 4 trillion-trillion 100W light bulbs World War II Fusionforenergy.com Fission or Fusion Fusion vs. Fission What kind of fuel can give such high temperatures and Pressure? 3

4 Proton-Proton (P-P) reaction Conditions for Fusion to Occur High Temperature (High Velocity) High Pressure High Density Density and Temperature in the Sun Gravity and Sun Hydrostatic Equilibrium A State When Gravity Compression = Gas Pressure Three Ways of Heat Transfer Sun Interior and Flow of Energy in the Sun Near the center, nuclear fusion reactions sustain high temperatures. Energy flows outward through the radiative zone as photons that gradually make their way to the surface as they are randomly deflected over and over by collisions with electrons. In cooler, more opaque outer layers the energy is carried by rising convection currents of hot gas (red arrows) and sinking currents of cooler gas (blue arrows 4

5 Life Time of the Sun What will happen when the Sun runs out of nuclear fuel? So How Long will the Sun Live with its Nuclear Fuel? T Life = /M sun 2 If M sun = 1, then T Life = years Common Misconception Acknowledgment Nuclear fusion in the Sun is tremendously powerful Truth: Only a tiny fraction of the hydrogen atoms are fusing into helium and are spread through a large volume in its core Truth: Gram for gram, you are a much more efficient heat producer than the Sun The Sun produces a lot of energy because it contains many grams of matter in its core The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. 5