The Sun’s Surface and Activity

The Sun’s Structure... Core: where nuclear fusion occurs 15 000 000 K H composition changes from about 35% at the centre to 65% at the edge Radiative Zone: 75% H, 23% He radiation is continually absorbed and re-emitted causes gamma rays to lose energy ( ‘random walk’)

Working our way outward... Once the light reaches the convection zone, it heats up the gases on the bottom, which then rise (since they are now more dense). They then give off the heat, so they cool and sink back down to the bottom of the zone. This process is called convection.

In the convection zone... The hot gases rising to the surface create hot and cool zones. The hot zones give of more light than the cool zones. As a result, the sun looks “grainy”. This is called granulation Convection Zone Radiative Zone

Granulation (sun spot in the centre)

Sun’s Surface... The photosphere is the deepest visible layer of the sun. The chromosphere is the pink layer 500 km -1000 km thick above the photosphere. The corona is a large area of increasing temperature (up to 3 million K) outside the sun.

Sun’s Surface... Sunspots are areas of high magnetic field. They are cooler that the rest of the surface, so they appear darker. The amount of sunspots at any given time is related to an 11 year cycle of solar activity (magnetic fluxuations). When the sun is “quiet”, the few sunspots occur at about 35o of latitude.

Solar Activity Some atoms get caught in strong magnetic loops on the surface and become prominences. These are much larger than sunspots. During especially high activity, an abundance of charged gases can escape from the surface in solar flares. These high energy particles will then travel to Earth. They often interfere with electronics on Earth.

These highly energized charged particles that are released from the solar surface become what is known as solar wind (< 300 km/s) These particles ‘clear out’ an area around the sun of most other gases. This is called the heliosphere and extends to at least 120 A.U. around the sun. This is one theoretical boundaries of the solar system. (The other being the edge of the Sun’s gravitational influence at the edge of the Oort Cloud)