The Sun. Our Sun is an ordinary star. Many stars are much more massive. Many stars are much less massive. What is the name of our Sun? What is the difference between a star and a sun?. Where the Sun came from? How old is the Sun? If the Sun has a surface?
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Our Sun is an ordinary star. Many stars are much more massive. Many stars are much less massive. What is the name of our Sun? What is the difference between a star and a sun?
Where the Sun came from? How old is the Sun? If the Sun has a surface? What are the layers of the Sun’s interior and exterior? The nature of sunspots? The connection between sunspots and the Sun’s magnetic field? What powers the Sun? Do You Know…….
Angular Momentum Cloud Cloud Cloud Collapses Begins Flattens Slowly to Flatten in to disk
Nuclear Fusion E = mc2
Know as the “P – P Chain” Matter is turned into anti-matter and energy
What Keeps the Star From Collapsing? Hydrostatic Equilibrium
The outward pressure force balances the inward gravitational force everywhere inside the Sun.
How Do We Know? Is thermonuclear fusion really taking place? • Detect the subatomic particles – Neutrinos • Nuclear burning produces ~1038 neutrinos/s • ~ 1014 neutrinos pass thru each m2 of Earth/s • ~1012 neutrinos pass thru your body each second • neutrinos have no electric charge • Neutrinos interact very weakly with matter • Rarely, a neutrino hits a neutron converting it into a proton 37Cl + neutrino => 37Ar Isotope reaction Rate of formation of 37Ar is proportional to neutrino flux Found 1 neutrino per day Expected 3 per day
1,000 tons of heavy water 9,600 light detectors
The Solar Interior Three main interior layers • Core • Radiation Zone • Convective Layer
Core • Central region of the Sun • Nuclear fusion occurs (also called hydrogen burning) • Star is born when fusion begins (about 1 million degrees) • Temp of core now about 15 million degrees
Radiative Zone • Section directly above the core • Energy moves by “radiation transport” • Photons travel ~1 cm before being absorbed • Photons take 106 to 108 yrs to reach surface • Random walk
Convective Region • Volume between radiative zone and surface • Energy is transported by convection • Cooler near the surface • Brings heat from interior to the surface • Similar to a pot of boiling water
The Surface of the Sun • Called the Photosphere • Bright visible surface from which light escapes • 300 to 400 km thick • Shell of hot, opaque gas Can’t see through this layer Completely transparent above Completely opaque below • Photosphere pressure ~ 10% of Earth’s sea level • Place where continuous spectrum is produced • Not a solid surface, density gradually increases w/depth
The Sun’s three interior layers. The Sun also has a surface and two atmospheric layers. Can you name them?
Computer Model Showing Solar Oscillations Blue zones moving outward Red zones moving inward Oscillations extend to core Study of Helioseismology Sun vibrates at many frequencies
The Atmosphere of the Sun Chromosphere Corona
Color Sphere, red Caused by bright red emission line Lies immediately above the photosphere Difficult to observe Reddish glow seen during a solar eclipse Coronograph – an occulting disk Source of most of the solar emission lines Composed of hot transparent gases – mostly H About 2,500 km thick Density decreases with altitude Temp increases from about 4,400 K to 25,000 K with altitude 100,000,000 times less dense then out atmosphere Chromosphere
Outer most layer of the Sun Extends millions of km above the photosphere Tenuous gas layer ~109 atoms/cc Earth ~1019 atoms/cc About 1 millionth as bright as the photosphere Temp in access of one million degrees Shape changes from month to month Spherical at sunspot maximum Corona
Pattern of light and dark areas on the photosphere • Are the light or dark areas hotter? • Lifetime about 5 to 10 minutes • Granules typically 700 km to 1000 kn in size • Granules are the tops of the convection currents of rising gas through the photosphere • Rise at about 2 to 3 km/s Granulation
Jets of gas surging upward into the corona Last about 15 minutes Speed ~ 20 km/s Chromosphere
Solar Wind • The Sun’s gravity keeps most gases from escaping • But high coronal temp cause speeds of 106 km/hr • The highest speed gases can escape • Sun ejects 106 tons of mass into the solar wind /s • Solar wind originates from coronal holes
Coronal Hole Movie Clip • Coronal hole is dark – devoid of material
1999 By observing the same group of sunspots, Galileo determined that the Sun rotates about once per week.