1. 24.3 The Sun

2. Structure of the Sun  Earth’s primary source of energy  Divide the sun into 4 parts  Solar interior  The visible surface (photosphere)  2 atmospheric layers (chromosphere & corona)

3. Structure of the Sun  Photosphere (light ball) (Sun’s surface)  Radiates most of the sunlight we see  Layer of gas  Grainy texture  Granules that are surrounded by narrow dark regions (size of TX)  Each granule survives 10-20 mins  Up and down movement is called boiling (convection)  90 % H 110 % Helium  Absorption spectrum

4. Continued…  Chromosphere (above photosphere)  Thin layer of hot gases  Observable only a few moments during a solar eclipse (or by a special instrument that blocks out light from the photosphere)  Hot incandescent gases under LP = emission spectrum

5. Continued…  Corona (crown)  Outermost portion of the solar atmosphere  Visible only when the photosphere is covered  Solar wind  Magnetic field prevents solar wind from reaching our surface  Radiates less energy bc of its very low density

6. The Active Sun  Sunspots (dark regions on the surface of the photosphere)  Appear darker bc of their temp. which is about 1500 K less than that of the surrounding solar surface  Prominences (huge cloudlike structures consisting of chromospheric gases  Look like gaint arches  Ionized gases trapped by magnetic fields that extend from regions of intense solar activity

7. Continued…  Solar Flares (brief outbursts that normally last about an hr & appear as a sudden brightening of the region above a sunspot  During their existence they release enormous amounts of energy (UV, Radio, & X-ray radiation)  Auroras (northern lights & southern lights)

8. The Solar Interior  Nuclear fusion (converts 4 H nuclei into the nucleus of a helium atom)  Lots of energy is released  Energy is released bc some matter is actually converted to energy  Energy is in the form of high-energy photons that work their way toward the solar surface  The photons are absorbed and reemitted many times until they reach a layer just below the photosphere

9. REVIEW  What is the structure of the sun?  Which layer of the sun can be thought of as its surface?  Are the same number of sunspots always present on the sun? Why or why not?  How much longer will the sun likely exist in its present state?  How does the sun produce energy?