Transcript 23sun4s
The Sun Astronomy 311 Professor Lee Carkner Lecture 23 Helios -- The God of the Sun The Sun was often worshiped by ancient people WARNING ! NEVER LOOK DIRECTLY AT THE SUN NEVER LOOK AT THE SUN WITH BINOCULARS OR A TELESCOPE PERMANENT EYE DAMAGE CAN RESULT Observing the Sun The solar surface is nearly featureless Much of our information about the Sun comes from multiwavelength observations, indirect measurements, and modeling The Sun From the Inside Out The solar interior is the source of solar energy which is transported to the surface Nuclear fusion and magnetic fields play key roles in the energetics and structure of the Sun Why Does the Sun Shine? From radioisotope dating we know that the solar system is 4.5 billion years old Chemical energy (burning) -Kelvin-Helmholtz contraction (gravitational energy) -Nuclear Fusion Reactions -- The Core At the core of the Sun the temperature and pressure are very high due to the weight of the outer layers At these conditions the hydrogen atoms are moving so fast and are packed together so tightly that they can fuse together to make helium: Hydrogen Fusion How Does the Energy at the Core Get Out? Energy in the Sun is transported in two ways: Radiation -Like a heat lamp Gas in this area is very hot and ionized and so doesn’t absorb the radiation very well Convection -- Like baseboard heating Cooler outer layers are less ionized and so absorb the radiation and heat up and rise The Inner Structure of the Sun The Photosphere It takes about 170,000 years for the energy to reach the surface of the Sun The visible surface of the Sun is called the photosphere The photosphere is the top of the convection zone Each about 1000 km across Granules Sunspots in the Photosphere The photosphere sometimes has small dark regions called sunspots Sunspots are regions where the Sun’s magnetic field inhibits the flow of warmer material Sunspots Sunspot Cycles Sunspots exist for a maximum of a few months There is a sunspot cycle of 11 years Just after sunspot minimum the spots appear at about 30 degrees north or south Sunspot Maximum and Minimum The Sunspot Cycle Sunspot Cycles and Differential Rotation The Sun rotates differentially The magnetic field gets “wrapped-up” around the equator Eventually the magnetic field is squeezed so tight it reconnects and cancels itself out The magnetic field prevents warmer material from flowing into the sunspots, so the sunspots are cooler than the rest of the photosphere The Twisted Magnetic Field of the Sun The Sun’s Magnetic Field It is twisted and tangled producing loops of magnetic force The Sun’s magnetic field is responsible for the structure and heating of the outer layers of the atmosphere The Solar Wind The magnetic fields in the outer layers of the Sun can accelerate material outward Interacts with the Earth’s magnetic field Very strong solar wind bursts can cause power and communication failures The Chromosphere The chromosphere is a diffuse layer of the solar atmosphere extending from the photosphere to about 2000 km It has a temperature of about 20000 K It is too thin for the atoms to collide and lose energy The Corona The corona is the outer layer of the Sun’s atmosphere It is thinner and hotter than the chromosphere This plasma emits strongly at ultraviolet and X-ray wavelengths Flares and Magnetic Activity The material in the corona is constantly changing They are both examples of magnetic activity During the Maunder Minimum in sunspot activity (1645-1715) it was very cold in Europe (The Little Ice Age) Core Radiative Zone Convective Zone Photosphere Chromosphere Corona Structure of the Sun Summary: Structure of the Sun Core fusion converts H to He and power the Sun Radiative Layer transports energy from the core Convective Layer transports energy to the photosphere Photosphere visible surface of the Sun Chromosphere hot middle atmospheric layer Corona very hot outer layer Summary: Solar Energetics Thermonuclear Fusion Energy is produced at the core of the Sun by converting hydrogen to helium Energy Transport Energy is transported via radiation where the opacity is low and via convection where the opacity is high Magnetic Fields The outer layers of the Sun are composed of hot plasma in magnetic loops