ASTR 101 Lecture 10 Outline of Last Lecture I. TelescopesA. Basic Telescope DesignB. Why Put Telescopes Into SpaceII. InterferometryIII. The SunOutline of Current Lecture I. The Suna. Physics of the sunb. Age of the sunII. Fission and FusionIII. Sun-Earth ConnectionsCurrent LectureThe Sun- Class M solar flares - normal- Class X solar flares - really, really dangerous, it rains down X-rays on the earth and messes with the magnetic field.- it takes approximately 8 minutes for the light from the sun to get to the Earth; it takes 205 days or the particles radiating from the sun to get to earth.- it is useless to go to Mars right now because there is so much radiation there that peoplewho go would come back with cancerPhysics of the Sun- We are going through major sunspot cycles so the temperature of the Earth is increasing. A few hundred years ago, the Sun because very quiet and the temperature on Earth dropped into a Mini-Ice Age.Minimum Age of the Sun- How long can the Sun burn by using its gravitational energy?- t = total energy / energy per second = the energy luminosity of the Sun = 18 million yearsKelvin Helmholtz Time- Known in the 1890s- Shows that the Universe cannot be 6000 years old- by 1920, Arthur Eddington knew that the Universe was older than 1 billion years and thought that stars burned H --> He- in 1939, Hans Bethe showed precisely how; he won the Nobel Prize for showing how theSun produces its energy.- The Sun is going to last approximately 10 billion years and it is roughly halfway through its lifeHow does the Energy Get Out of the Sun?- It takes a million years for the photon to "walk" outside the Sun. So if the Sun went out tomorrow, went out as in all reaction stopped, we'd still have a million years of the light locked inside.- Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons.Fission: Big nucleus splits into smaller pieces (nuclear power plants)Fusion: Small nuclei stick together to make a bigger one (Sun, stars)Hydrogen Fission by the Proton-Proton ChainStep 1: Two protons fuse to make a deuterium nucleus (1 proton and 1 neutron). This step occurs twice in the overall reactionStep 2: The deuterium nucleus and a proton fuse to make a nucleus of helium-3 (2 protons, 1 neutron). this step also occurs twice in the overall reactionStep 3: Two helium-3 nuclei fuse to form helium-4 (2 protons, 2 neutrons), releasing two excess protons in the process.Proton-proton chain is how hydrogen fuses into helium in the Sun.Solar Thermostat- Decline in core temperature causes fusion rate to drop, so core contracts and heats up.- Rise in core temperature causes fusion rate to ruse, so core expands and cools down.Internal Rotation- False color image showing a theoretical model of relatively hotter and colder regions in the solar interior- The red layer may be a shear region between the radiative and convective zones, powering a dynamo that gives rise to the sun's magnetic field.How does Energy get out from the core? ConvectionHow do we know what is happening on the inside of the Sun?- By studying the frequencies of the vibrations of the Sun we can tell what it's made of- Patterns of vibrations on the surface tell us about what the Sun is like on the inside- Stellar oscillations: acoustic, gravity, surface gravity- Data on solar vibrations agree with mathematical models of the solar interiorNeutrinos- Are ghost-like particles that don't act on matter except by the weak force-Travel almost at the speed of light-Come out of the Sun almost as if the Sun is transparent-Have some mass so they aren't like neutrons-They have tons of energy, but no way to deposit it anywhere- Created during fusion fly directly through the Sun- Observations of these solar neutrinos can tell us what's happening in the coreSolar neutrino problem: Early searches for solar neutrinos failed to find the predicted number.More recent observations find the right number of neutrinos, but some have changed form.10.3 The Sun-Earth ConnectionSolar activity is like "weather" on Earth.Sun's Magnetic Field- The sun's corona is threaded with a complex network of magnetic fields. Solar storms of flares result from changes in the structure and connections of these fields.- Loops of bright gas often connect sunspot pairs.- Charged particles spiral around magnetic field lines.- Charged particles streaming from the Sun can disrupt electrical power grids and disable communications satellitesSunspots- Are cooler than other parts of the Sun's surface (4000 K)- Are regions with strong magnetic fields- Always come in pairs (have to have two
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