24.3 The Sun
� There are 100 billion stars in the Milky Way
� The Sun is Earth’s primary source of energy
� Compared to other stars, the Sun is an “average” star.
Structure of the Sun
� The sun can be divided up as
follows:
� Interior
�Surface (Photosphere)
�Atmosphere
�Chromosphere
�Corona
The Interior� Deep inside the interior, the sun
produces energy by nuclear fusion
� Four hydrogen nuclei are converted into the nucleus of a helium atom
� Tremendous energy is released
� Some matter is actually converted to energy
The Interior� Know E = mc2
� As hydrogen is consumed, the product of this reaction—helium—forms the solar core, which continually grows in size.
� The sun has enough fuel to last another 100 billion years.
The Surface (Photosphere)
� The photosphere radiates most of the sunlight we see and can be thought of as the visible “surface” of the sun
� Has granules
� 90% of the surface atoms are hydrogen
The Atmosphere—Part 1--Chromosphere
� Appears as a red rim around the sun
� Thin layer
� Observable for a few moments during a solar eclipse
The Atmosphere—Part 2--Corona
� Outermost part of the atmosphere
� Also visible only during an eclipse—produces a glow
� Produces the solar wind
The Active Sun--Sunspots� Dark regions on the surface of the
photosphere are called sunspots
� They appear dark because they are cooler than the surrounding surface
The Active Sun--Prominences
� Prominences are huge cloudlike structures consisting of gasses
� They often appear as great arches that extend well into the corona
� Prominences are ionized gases trapped by magnetic fields that extend from regions of intense solar activity.
The Active Sun—Solar Flares� Solar flares are brief outbursts that
appear above a sunspot cluster
� They release a large amount of energy
� They are relatively rare
� They produce auroras
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