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The_Sun.ppt
- 1. Visible Image ofthe Sun The Sun •Our sole source of light and heat in the solar system •A very common star: a glowing ball of gas held together by its own gravity and powered by nuclear fusion at its center.
- 2. Pressure (from heat causedby nuclear reactions) balances the gravitational pull toward the Sun’s center. Called “Hydrostatic Equilibrium. This balance leads to a spherical ball of gas, called the Sun. What would happen if the nuclear reactions (“burning”) stopped?
- 3. Main Regions ofthe Sun
- 4. Radius = 696,000km (100 times Earth) Mass = 2 x 1030 kg (300,000 times Earth) Av. Density = 1410 kg/m3 Rotation Period = 24.9 days (equator) 29.8 days (poles) Surface temp = 5780 K Solar Properties The Moon’s orbit around the Earth would easily fit within the Sun!
- 5. Luminosity of theSun = LSUN Solar constant: LSUN / 4R2 (energy/second/area at the radius of Earth’s orbit) (Total light energy emitted per second) ~ 4 x 1026 W 100 billion one- megaton nuclear bombs every second!
- 6. The Solar Interior “Helioseismology” •Inthe 1960s, it was discovered that the surface of the Sun vibrates like a bell •Internal pressure waves reflect off the photosphere •Analysis of the surface patterns of these waves tell us about the inside of the Sun How do we know the interior structure of the Sun?
- 7. The Standard SolarModel
- 8. Energy Transport withinthe Sun • Extremely hot core - ionized gas • No electrons left on atoms to capture photons - core/interior is transparent to light (radiation zone) • Temperature falls further from core - more and more non-ionized atoms capture the photons - gas becomes opaque to light in the convection zone • The low density in the photosphere makes it transparent to light - radiation takes over again
- 9. Convection Convection takesover when the gas is too opaque for radiative energy transport. Hot gas is less dense and rises (or “floats,” like a hot air balloon or a beach ball in a pool). Cool gas is more dense and sinks
- 10. Solar Granulation Evidence for Convection Solar Granules are the tops of convection cells. Bright regions are where hot material is upwelling (1000 km across). Dark regions are where cooler material is sinking. Material rises/sinks @ ~1 km/sec (2200 mph; Doppler).
- 11. The solarspectrum has thousands of absorption lines More than 67 different elements are present! Hydrogen is the most abundant element followed by Helium (1st discovered in the Sun!) The Solar Atmosphere Spectral lines only tell us about the part of the Sun that forms them (photosphere and chromosphere) but these elements are also thought to be representative of the entire Sun.
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- 13. Chromosphere (seen duringfull Solar eclipse) Chromosphere emits very little light because it is of low density Reddish hue due to 32 (656.3 nm) line emission from Hydrogen
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- 15. Chromospheric Spicules: warm jetsof matter shooting out at ~100 km/s last only minutes Spicules are thought to the result of magnetic disturbances H light
- 16. Transition Zone andCorona
- 17. Transition Zone & Corona Why does the Temperature rise further from the hot light source? We see emission lines from highly ionized elements (Fe+5 – Fe+13 ) which indicates that the temperature here is very HOT Very low density, T ~ 106 K magnetic “activity” -spicules and other more energetic phenomena (more about this later…)
- 18. Corona (seen duringfull Solar eclipse) Hot coronal gas escapes the Sun Solar wind
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- 20. Solar Wind Coronalgas has enough heat (kinetic) energy to escape the Sun’s gravity. The Sun is evaporating via this “wind”. Solar wind travels at ~500 km/s, reaching Earth in ~3 days The Sun loses about 1 million tons of matter each second! However, over the Sun’s lifetime, it has lost only ~0.1% of its total mass.
- 21. Hot coronal gas(~1,000,000 K) emits mostly in X-rays. Coronal holes are sources of the solar wind (lower density regions) Coronal holes are related to the Sun’s magnetic field
- 22. Most of theSolarluminosity is continuous photosphere emission. But, there is an irregular component (contributing little to the Sun’s total luminosity). The Active Sun UV light
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- 24. Sunspots • Typically about10000 km across • At any time, the sun may have hundreds or none • Dark color because they are cooler than photospheric gas (4500K in darkest parts) • Each spot can last from a few days to a few months • Galileo observed these spots and realized the sun is rotating differentially (faster at the poles, slower at the equator)
- 25. Sunspots & Magnetic Fields •Themagnetic field in a sunspot is 1000x greater than the surrounding area •Sunspots are almost always in pairs at the same latitude with each member having opposite polarity •All sunspots in the same hemisphere have the same magnetic configuration
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- 28. The Sun’s differentialrotation distorts the magnetic field lines The twisted and tangled field lines occasionally get kinked, causing the field strength to increase “tube” of lines bursts through atmosphere creating sunspot pair
- 29. Sunspot Cycle Solar Cycleis 22 years long – direction of magnetic field polarity flips every 11 years (back to original orientation every 22 years) Solar maximum is reached every ~11 years
- 32. Charged particles(mostly protons and electrons) are accelerated along magnetic field “lines” above sunspots. This type of activity, not light energy, heats the corona. Heating of the Corona
- 33. Charged particles followmagnetic fields between sunspots: Solar Prominences Sunspots are cool, but the gas above them is hot!
- 34. Earth Solar Prominence Typical sizeis 100,000 km May persist for days or weeks
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- 36. Very large solarprominence (1/2 million km across base, i.e. 39 Earth diameters) taken from Skylab in UV light.
- 37. Solar Flare andResulting Prominence
- 38. Solar Plages andFilaments
- 39. Solar Flare, Prominenceand Filament
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- 41. SOLAR-TERRESTRIAL RELATIONSHIPS • AURORAE •SOLAR WIND • MAGNETIC STORMS • RADIO FADEOUTS • COSMIC RAYS • WEATHER (?)
- 42. The Proton-Proton Chain: 4 H He Whatmakes the Sun shine? Nuclear Fusion
- 43. E = mc 2 (c = speed of light) But where does the Energy come from? c2 is a very large number! A little mass equals a LOT of energy. Example: 1 gram of matter 1014 Joules (J) of energy. Enough to power a 100 Watt light bulb for ~32,000 years!
- 44. Mass “lost” isconverted to Energy: Mass of 4 H Atoms = 6.693 10-27 kg Mass of 1 He Atom = 6.645 10-27 kg Difference = 0.048 10-27 kg (Binding Energy, ordinarily expressed in MeV) (% m converted to E) = (0.7%) E = m c 2 (c = speed of light) But where does the Energy come from!? The total mass decreases during a fusion reaction. The sun has enough mass to fuel its current energy output for another 5 billion years
- 45. Nuclear fusionrequires temperatures of at least 107 K – why? Atomic nuclei are positively charged they repel via the electromagnetic force. Merging nuclei (protons in Hydrogen) require high speeds. (Higher temperature – faster motion) At very close range, the strong nuclear force takes over, binding protons and neutrons together (FUSION). Neutrinos are one byproduct.
- 46. Neutrinos are almost non-interactingwith matter… So they stream out freely. Neutrinos provide important tests of nuclear energy generation. The energy output from the core of the sun is in the form of gammy rays. These are transformed into visible and IR light by the time they reach the surface (after interactions with particles in the Sun).
- 47. Solar Neutrino Problem:There are fewer observed neutrinos than theory predicts (!) A discrepancy between theory and experiments could mean we have the Sun’s core temperature wrong. But probably means we have more to learn about neutrinos! (Neutrinos might “oscillate” into something else, a little like radioactive decays…) Detecting Solar Neutrinos – these light detectors measure photons emitted by rare chlorine-neutrino reactions in the fluid.