The Sun

• Distance from Earth: 150 million km OR 93 million miles

• Size: 1.4 million km in diameter

• Age: 4.5 billion years old, halfway through its 10 billion year “lifetime”

Sun Composition

• Plasma, which is a gas in which atoms are ionized from high temperatures. They create and react to magnetic fields.

• Hydrogen = 70%, Helium = 28%, Trace gases (carbon, oxygen, nitrogen, neon) = 2%

Processes inside the Sun

• Nuclear Fusion – called the Sun Fusion Model– Converts 4 Hydrogen nuclei to 1 Helium Nucleus– 400 million tons of Hydrogen are converted to

Helium every second– Produces 1 photon of light (which is why the stars

shine)– Supported Einstein’s Theory E=mc2 (Energy is

equal to mass times the speed of light squared)

Processes inside the Sun

• Stability created by gravitational pull inward and pressure pushing outwards.– Called Gravitational Equilibrium– Pressure must increase with depth causing gases

to be hot and dense allowing nuclear fusion in the core.

Facts about the Sun

• 1 million Earth’s would fit inside the Sun.• Some ancient cultures worshipped the Sun as

a God.• The Sun is necessary for all life on Earth by

providing heat, light and energy.

The Structure of the Sun

• Core – approximately 27 million °F. It is the hottest part of the Sun. The core is a Solar Thermostat.

Increase core temperature

Fusion rate increases.

Core pressure will increase.

Core expands and cools

Restores fusion

Decrease core temperature

Fusion rate decreases.

Core pressure will decrease.

Core contracts and heats up

Restores fusion

The Structure of the Sun

• Radiation Zone – energy moves outward from core in the form of light.

The Structure of the Sun

• Convection Zone – circulates huge streams of bubbling gases.– Hot gas rises, cool gas sinks.

The Structure of the Sun’s Atmosphere

• Photosphere – yellow surface that is visible made of individual cells called granules.– Low Density– About 400 km thick, holds in the heat produced.

The Structure of the Sun’s Atmosphere

• Chromoshpere – above, photosphere, 10,000 km thick and can be seen during an eclipse.

The Structure of the Sun’s Atmosphere

• Coronasphere – known as the “Corona”, above chromosphere and can also be seen during total solar eclipse. Hottest layer of Sun’s atmosphere.

Sunspots• A dark, cooler area on the photosphere. (Only darker because

they are less bright/have less color than surrounding photosphere.

• Occurrences tied to magnetic cycle and are where tightly wound magnetic fields block convection in the area and poke nearly straight out from solar interior. No new hot plasma=less heat=darker.

• Shows evidence that the Sun rotates and can last for a few weeks.

• Average time between may points during sunspot cycle= 11 years (max=15 years, minimum=7 years)

• Solar Cycle is 22 years – takes 2 sunspot cycles for magnetic fields to revert to the way it started.

• First discovered in 5 B.C. by the Chinese

Solar Storms

• Affects humans by disrupting radio communications, disrupts electrical power, damage electronic components in orbiting satellites.

Solar Prominence

• A storm on the dark central core part of the photosphere that is magnetic field related. A physical characteristic that may appear red due to hydrogen in the sun.

Solar Flare

• Explosions that erupt from the surface during the sunspot cycle max point.

Solar Wind

• Streams of ions and electrons that flow outward from the sun in all directions.

• The solar wind helps shape the magnetosphere of planets.

• Blows back the material that forms the plasma tail of comets.

Coronal Mass Ejections

• Highly energetic charged particles from the Corona that reaches Earth in several days.

• Creates a geomagnetic storm in Earth’s magnetosphere forming strong auroras.

Auroras• Called “aurora borealis” or Northern Lights in in the

Northern Hemisphere.• Called “aurora australis” or the Southern Lights in

the Southern Hemisphere.• Caused by particles given off by solar wind and

coronal mass ejections and hit the oxygen and nitrogen gases in the atmosphere causing atoms to give off colored light.

• Are typically only observed from high latitudes and can be seen from space. Lights can look light surf in the upper atmosphere in mostly green and white.

How do we know all this stuff?• Mathematical Models – models that use the laws of physics

to predict internal conditions.• Solar Vibration – from movement of gas within the sun

observed on the Sun’s surface by looking for Doppler Shift.• Solar Neutrinos – subatomic particle produced by nuclear

fusion in the core.• Solar Telescopes/Observatories – projects large images of the

sun and observe changes that occur on the surface of the sun.• Satellites – used to study solar radiation

– 1973 – Sky Lab – took pictures and made observations of the sun– 1980 – Solar Max – studied sunspot activity.

• Other – NASA TRACE mission and SOHO spacecraft mission (2003) – study solar storms.

The End