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The Sun: A Garden -Variety Star

The Sun: A Garden -Variety Star. The Sun. Biggest object in the solar system diameter 1,392,000 km 109 x Earth’s diameter 10 x Jupiter’s diameter Most Massive 333,000 x Earth’s mass 1,000 x Jupiter’s mass so heavy, everything else orbits around it!

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The Sun: A Garden -Variety Star

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  1. The Sun:A Garden -Variety Star AST 2010: Chapter 14

  2. The Sun • Biggest object in the solar system • diameter 1,392,000 km • 109 x Earth’s diameter • 10 x Jupiter’s diameter • Most Massive • 333,000 x Earth’s mass • 1,000 x Jupiter’s mass • so heavy, everything else orbits around it! • so heavy, it makes its own heat and light • Temperature of 15,000,000 K in its core • nuclear power! AST 2010: Chapter 14

  3. The Sun’s Profile AST 2010: Chapter 14

  4. The Sun’s Composition • The Sun contains the same elements as the Earth, but not in the same proportions • About 73% of the Sun’s mass is comes from hydrogen, and another 25% from helium • Other chemical elements make up the rest 2% • The fact that the Sun are mostly made up of H and He was first shown by Cecilia Payne-Gaposchkin • The 1st woman to get a PhD in astronomy in the U.S. AST 2010: Chapter 14

  5. The parts of the Sun AST 2010: Chapter 14

  6. The Sun's Interior • From inside out: • Core • Radiative zone • Convection zone • Photosphere • Chromosphere • Transition region • Corona AST 2010: Chapter 14

  7. The Sun's Core • The core • is the innermost 10% of the Sun's mass • generates energy from nuclear fusion • has the highest temperature and density • temperature 10 million K • density = 160 x density of water = 20 x density of iron • at this temperature, the core is a gas • no molten interior AST 2010: Chapter 14

  8. How does Heat from the Core Reach Us? • Three ways to transfer heat: • Conduction: direct contact • A spoon in a hot cup of coffee gets warm • Convection: moving currents in a fluid • Hot air rises • Hot current in boiling water • Radiation: electromagnetic waves emitted by a heat source and absorbed by a cooler material • Electric stove • Heat from the Sun reaches us through the EM waves it emits AST 2010: Chapter 14

  9. Radiative Zone • Radiation transfers heat from the interior of the Sun to its "cooler" outer layers • The core & radiation zone make up 85% of the Sun • The temperature drops from 10 million K at the inner side of the radiative zone to 2 million K at its edge • The energy generated in the core is carried by photons that bounce from particle to particle through the radiative zone • The photons are too energetic to be absorbed by atoms • Each photon bounces so many times that it is estimated to take one million years to reach the outer edge of the region AST 2010: Chapter 14

  10. cool hot Convection Zone • Matter at the base of the convection zone is “cool” enough (2 million K) for the atoms to absorb energy and hold on to it • Convection occurs in this region • The hotter material near the top of the radiation zone (the bottom of the convection zone) rises while the cooler material sinks — heated below like a pot of boiling water • It takes a week for the hot material to carry its energy to the top of the convection zone convection zone radiative zone AST 2010: Chapter 14

  11. Photosphere • This is the Sun’s deepest layer that one can see from the outside • Photosphere means “light sphere” • It is the visible “surface” of the Sun • From this layer, photons can finally escape to space • The surface is not something one could land or float on • The photosphere is about 500 km thick • The gas is so dense that you could not see through it • The gas emits a continuous spectrum of light • It features sunspots AST 2010: Chapter 14

  12. Temperature of Photosphere • The photosphere temperature is about 5,800 K • The sunspots appear darker because they are cooler than their surroundings • The center of a typical sunspot has a temperature of 4,000 K • The spectrum and energy output of the radiation emitted from the photosphere obey Wien’s Law and Stefan-Boltzmann law AST 2010: Chapter 14

  13. Features of Photosphere • granules • tops of convection cells • 700 to 1000 km diameter • last 10 minutes • centers ~ 100 K hotter than edges • Sunspots • dark spots, 1500 K, cooler than surroundings • glow by themselves AST 2010: Chapter 14

  14. Sunspots • Discovered by Galileo Galilei • Sun's surface sprinkled with small dark regions - sunspots • Sunspots are darker because they are cooler by 1000 to 1500 K than the rest of the photosphere • Spots can last a few days or as long as a few months  • Galileo used the longer-lasting sunspots to map the rotation patterns of the Sun • Sunspots number varies in a cycle with an average period of 11 years • Cycle starts with minimum and most of them are at around 35° from the solar equator • At solar maximum (number peaked), about 5.5 years later, most of the sunspots are within just 5° of the solar equator AST 2010: Chapter 14

  15. AST 2010: Chapter 14

  16. AST 2010: Chapter 14

  17. Sunspots and Magnetic Field • Sunspots = regions of strong magnetic fields • Found by observation of Zeeman effect AST 2010: Chapter 14

  18. Sun Rotates • Galileo • discovered sunspots • sunspots moved  sun rotates • Rotation – speed depends on latitude • equator once/25 days • 30º N once/26.5 days • 60º N once/30 days • Jupiter also does this AST 2010: Chapter 14

  19. AST 2010: Chapter 14

  20. Chromosphere • Visible during solar eclipses as a thin pink layer at the edge of the dark Moon • Colorful layer – “color sphere” • Color due to hydrogen bright emission line • Also shows yellow emission due to helium – discovered in 1868 – new element previously not seen on Earth • Helium was found on Earth in 1895 • The chromosphere is only 2,000 to 3,000 km thick • Temperature rises outward away from the photosphere – from 4,500 K to 10,000 K AST 2010: Chapter 14

  21. Transition Region • It’s a thin region (about 10 km thick) in the Sun’s atmosphere where temperature changes from 10,000 K to nearly 1,000,000 K AST 2010: Chapter 14

  22. Solar Weather • The Sun has complex and violent weather patterns • Chromosphere contains jet-like spikes of gas – called spicules • Spicules rise vertically through the chromosphere • Last 10 minutes • Consist of gas jets, at 30 km/s • Rise to heights of 5000 to 20000 km • T ~ chromosphere AST 2010: Chapter 14

  23. Corona (1) • The outermost part of the Sun’s atmosphere is called the corona • It is visible during total solar eclipses as a pearly-white glow around the dark Moon  • The corona has a very high temperature of ~1-2 million K • It is known to be very hot because it contains multiply ionized atoms • At very high temperatures, atoms like iron can have 9 to 13 electrons ejected (the atoms become ionized) • 9-times ionized iron is only produced at a temperature of 1.3 million K • 13-times ionized iron means the temperature gets up to 2.3 million K!  Total solar eclipse in 1973 AST 2010: Chapter 14

  24. Corona (2) • Most of the corona is trapped close to Sun by loops of magnetic field lines • In X-rays, those regions appear bright • Some magnetic field lines do not loop back to the Sun and will appear dark in X-rays • These are called coronal holes • More details visible at short wavelengths • A solar eclipse photographed in the extreme ultraviolet taken by the SOHO spacecraft  AST 2010: Chapter 14

  25. X-rays from the Corona AST 2010: Chapter 14

  26. Prominences • Bright clouds of gas forming above the sunspots • Quiet prominences • 40,000 km above surface • Last days to several weeks • Eruptive prominences • 700 km/s • Rare • Surge prominences • Last up to a few hours • Shoot gas up to 300,000 km • Gas speed ~1300 km/s AST 2010: Chapter 14

  27. Prominences follow magnetic-field loops AST 2010: Chapter 14

  28. AST 2010: Chapter 14

  29. AST 2010: Chapter 14

  30. Solar Flares • Solar flares are eruptions more powerful than surge prominences • Flares last from a few minutes to a few hours • A lot of ionized material is ejected in a flare • Unlike the material in prominences, the solar-flare material moves with enough energy to escape the Sun's gravity • When such a burst of ions reaches the Earth, it interferes with radio communication • Sometimes a solar flare will cause voltage pulses or surges in power and telephone lines • Brownouts or blackouts may result • Humans traveling outside the protection of the Earth's magnetic field will need to have shielding from the powerful ions in a flare AST 2010: Chapter 14

  31. AST 2010: Chapter 14

  32. Solar Wind • Fast-moving charged particles (mostly protons and electrons) can escape the Sun's gravitational attraction • The stream of particles is called the solar wind • They move outward at a speed of about 400 km/s • They can reach the farthest reaches of the solar system • Solar-wind particles passing close to a planet with a magnetic field are deflected around the planet • Some are deflected to the planet's magnetic poles • As the particles hit the planet's atmosphere, they cause the molecules in the atmosphere to produce beautiful curtains of light called the auroras • Aurora borealis in the northern hemisphere • Aurora australis in the southern hemisphere AST 2010: Chapter 14

  33. Is the Sun a Variable Star? • What is more certain than that the Sun will rise tomorrow? • We’ve already seen that sunspots follow an 11-year cycle • On longer time scales, the Sun undergoes changes in overall activity • Changes are only about 0.1%! • Yet this is enough to affect our climate • In the mid 1600’s the Sun’s output was particularly low  the “Little Ice Age” • Other stars are seen to vary by 0.3%, up to 1% AST 2010: Chapter 14

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