The Sun

ROBOTSSummer 2008

Solar Structure• Core - the center of the Sun where nuclear fusion releases a large amount of heat energy and converts hydrogen to helium. The density of the core is 150 times the density of water on Earth.

Convection

Solar Structure• Fusion - when atomic particles join together to create heavier atoms. Large amounts of energy are either released or absorbed in the process. In the sun, fusion combines hydrogen to made helium.

Solar Structure• Radiative zone - the layer of the Sun just outside the core and makes up most of the Sun. Thermal radiation carries the heat created in the core out to the outer layers of the Sun.

• Convective Zone - In this layer the Sun is not hot or dense enough for radiation so thermal columns carry hot material to the surface (photosphere) of the Sun. When it cools, it drops back down to get more heat from the radiative zone.

Convection

Solar Structure• Photosphere - the visible surface of the Sun where light and heat energy leave the Sun.

• Granules - the top of the thermal columns that carry hot matter from inside the Sun to the surface. The hottest material is in the center and cooler materials are near the edges falling back down.

Convection

Sun Spots• Sunspot - areas on the photosphere where strong magnetic fields stop convection making cool spots on the surface of the Sun that appear dark.

Medium size spots are about the same diameter as the Earth!

• Central region is called the umbra

• Lighter region is called the penumbra

• Granules appear all over the Sun

Earth

Sunspots

Sun Spots

• Solar cycle - an 11-year cycle of activity on the Sun. At solar minimum there are few sunspots and solar flares. Right now we are leaving solar minimum and beginning to see an increase in solar activity.

Sunspots Cycle

Solar Structure• Chromosphere - the part of the Sun's atmosphere closest to the surface. It has a distinctive red color because of the red spectral line from hydrogen. Scientists still don't understand why the chromosphere is hotter then the photosphere.

• Corona - the last layer of the Sun's atmosphere that extends millions of miles into space. It is visible during a total solar eclipse. The outer edges of the corona are constantly carried away by solar winds.

Convection

X-ray View

Solar Activity

• Solar flare - a violent plasma explosion in the Sun's corona and chromosphere. Solar flares usually occur near sunspots.

• Coronal mass ejection (CME) - large amounts of plasma thrown out of the Sun's corona. When a CME reaches the Earth it can disrupt power, satellite communications and cause aurora.

Aurora

• Aurora - colored lights produced over the Earth's poles and caused by interactions between CMEs from the Sun and the Earth's magnetic field.

Solar Activity• Solar wind - a stream of plasma (high energy electrons and protons) from the corona of the Sun.

• Geomagnetic storm - disturbance in the Earth's magnet field caused by space weather such as solar winds, CME and solar flares. These storms can disrupt power, satellite communications and cause aurora.