A105 Stars and Galaxies Homework 6 due today Next Week: Rooftop Session on Oct. 11 at 9 PM Reading: 54.4, 55, 56.1, 57.3, 58, 59 Todays APODAPOD READING FOR NEXT WEEK Background material in 54, 56, 57: 54.4: magnitude system 56.1: types of binary stars 57.3: Stefan-Boltzman Law Key topics (read carefully!): 55: Temperatures and Compositions of Stars 58: The H-R Diagram 59: Stellar Evolution Basic Facts radius 7 x 10 5 km about 100 x Earths radius mass = about 300,000 x Earths mass distance 1 AU, 8 light minutes 1.5 x 10 8 km about 100 x Suns diameter Temperature about 6000 Kelvin (10,000 F) at the surface about 15 million Kelvin inside Composition 90% of atoms are hydrogen 10% of atoms are helium The Sun What we covered on Tuesday: Internal structure of the Sun Composition of the Sun Source of the Suns energy The Suns lifetime Balancing pressure, gravity, and temperature Helioseismology What neutrinos tell us about the Sun Today: The Suns Atmosphere Recall the structure of the Sun Corona The Suns Atmosphere: Photosphere, Chromosphere, Corona, Solar Wind Photosphere Umbra Penumbra Sunspots Active regions The Sun Corona Chromosphere three layers of the Suns atmosphere photosphere chromosphere corona Photosphere Limb Convection Supergranules Granulation Limb darkening Umbra Penumbra Sunspots Active regions Prominence Limb darkening: when we look near the Suns limb we do not see as deeply into the photosphere Photosphere The photosphere is opaque to visible light The density is only 1% the density of air Temperature decreases from inside the Sun to a minimum of 4400K just above the photosphere Granulation: convection cells ~ 1000 km (600 mi) The difference in T from center to edge is about 300 K -> hot gas from lower levels rises upward, cools off, and falls back into the Sun Cells form and disappear in few minutes. The Solar Photosphere the layer we see The convection moves at 1400 km/h =900 mi/h Supergranules last about a day Supergranules 35,000 km in diameter Absorption Lines in the Photosphere Photosphere nearly a perfect thermal radiator with T=5800 K *upper part of the photosphere is 4400K (cooler!) Solar Atmosphere Absorption lines from the photosphere and chromosphere 67 different elements in various stages of excitation and ionization The spectrum gives us a picture of the physical conditions in the solar atmosphere Sunspot grouping Umbra Penumbra Blotchy sunspots appear on the Suns surface Note also the granulation resulting from convection under the surface Sunspots are low-temperature regions in the Suns photosphere Sometimes they are isolated but frequently in sunspost groups ~ diameter of Earth (lasting between hours or months) T (umbra) = 4300 K T (penumbra) = 5000 K T (photosphere = 5800 K The brightness depends on the 4 th power of the temperature (energy flux T 4 ) Photosphere The number of sunspots varies in an 11 years cycle Magnetic Carpet Chromosphere Spicules Prominence Above the photosphere, the temperature increases again from 4400 K to 25,000 K at the top of the chromosphere The chromosphere is characterized by spikes of rising gas Above the photosphere, the gas density is much lower (10 -4 less than the photosphere) but gas is much warmer (25,000 K) Red color from the emission line of hot hydrogen (Using Hydrogen filter) Spicules last about 15 minutes they rise at speeds of 20km/s 300,000 spicules cover the Sun at any one time Spicules: jets of rising gas Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules dense jets of gas that shoot up from the chromosphere Solar Wind Coronal Mass Ejection Corona Aurora Coronal Holes The corona, the outermost layer of the solar atmosphere, is made of very high- temperature gases at extremely low density The solar corona blends into the solar wind at great distances from the Sun CORONA The corona extends for millions of kilometers out from the Sun a million times fainter than the photosphere... In the narrow region between the chromosphere and the corona, the temperature rises abruptly to more than a million degrees! (BUT NOT MUCH HEAT!) Activity in the corona includes coronal mass ejections and coronal holes The Sun also produces huge flares that burst into space A solar flare is a brief eruption of hot, ionized gases from a sunspot group A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona The Solar Wind The Sun is evaporating constantly (ONLY 0.1% of its mass since its formation) Interact with objects in the solar system Earth: cause aurorae Comets: produces tails Interacts with edge of solar system: heliopause Radiation reach Earth in 8 min, particles take a few days (v= 500 km/s) Coronal particles (mostly electrons and protons) are thrown with such velocity that they cannot be held by the Suns gravity Photosphere Limb Convection Supergranules Granulation Limb darkening Umbra Penumbra Sunspots Active regions The Sun Magnetic Carpet Solar Wind Coronal Mass Ejection Corona Aurora Coronal Holes Chromosphere Spicules Prominence The X-ray Sun coronal hole What causes all this violent activity on the Sun????? Rotation and Magnetic Fields! mass ejectio n Sunspots show the Sun is rotating (Galileo!) The Sun does not rotate rigidly: the equatorial regions rotate faster (25 days) than the poles (36 days) --- Differential Rotation The Sun rotates at different rates at different solar latitudes P equator =25 days P pole =36 days The Suns differential rotation winds up the Suns magnetic field, storing energy. When the magnetic field suddenly unwinds, that energy is released. The Solar Magnetic Field The differential rotation wraps up the magnetic field of the Sun Sunspots and other solar activity are caused by the twisted magnetic field of the Sun Solar Activity Varies in an Eleven Year Cycle The Suns magnetic field takes 11 years to twist up and then reestablish itself The number of sunspots, as well as the number of violent events depends on the state of the magnetic field Variations in Sunspot Activity Maunder Minimum Stars! Units (parts) Homework 7 Due THURS. HAND IN HOMEWORK!