Chapter 20.2

The Sun:

Our Very Own Star

Structure of the Sun

• The sun is basically a large ball of gas– Made mostly of Hydrogen and Helium – Held together by Gravity

• May appear to have a solid surface– No– Visible surface starts where gases are so

thick, you can’t see through it.

Layers of the Sun

Structure of the Sun

Energy Production

Scientists believed:

• Sun burned fuel to generate energy– (would only last for 10,000 years)

• Gravity was causing sun to shrink and gravity would release energy to heat sun– (would only last for 45 million years)

• Sun has been shining for 4.6 billion years

Nuclear Fusion• Albert Einstein showed that matter and

energy are interchangeable- E=mc² – (E-energy, m-mass, c- speed of light)

• Since c is such a large number, tiny amounts of matter can produce a huge amount of energy.

• Nuclear fusion= process by which two or more low-mass nuclei fuse to form one larger nucleus

• 4 H → 1 He = Energy (Sun’s energy)

Nuclear Fusion

Fusion in the Sun• Core

– Where energy is produced (nuclear fusion)

• Radiative Zone– Very dense, energy passes through here

• Convective Zone– Hot gases circulate here when energy passes

• Photosphere– Visible portion where energy leaves sun as light– Takes 8.3 minutes to reach Earth

Solar Activity

• Convection of hot gases + sun’s rotation=

Magnetic Fields

• Solar wind– Constant flow of magnetic fields from sun– Can cause interference with the Earth’s

magnetic field disrupting TV signals and damaging satellites

Solar Wind

Sunspots

• The sun’s magnetic fields tend to slow down activity in the Convective zone.

• When activity slows down, some areas of the Photosphere become cooler.

• These cooler areas show up as Sunspots.

• These cooler, darker spots cycle every 11 years and have been linked to low temperatures on Earth’s surface.

Sunspots

Solar Flares

• Magnetic fields can also cause regions of extremely high temps and brightness that develop on the sun’s surface.

• When solar flares erupt, it sends huge streams of electrically charged particles into the solar system.

• Solar flares can interrupt radio communications on the Earth and in orbit.

Solar Features