Chapter 20, Section 2The Sun

Anne Marie Scrudato’s notes

borrowed by Rusty Sturken

Fusion• The sun’s gravity is by far the most powerful

force in the solar system • The sun’s energy comes from nuclear fusion. • In the process of nuclear fusion, inside the

sun, hydrogen atoms are combined to make helium.

• When two hydrogen atoms become one helium atom through fusion some mass is lost. The helium atom has less mass than the two hydrogen atoms. This mass is converted directly to energy E=mc²

Fusion

http://entergy.apogee.net/kids/graphics/lnh2.jpg

The Sun’s Core• The sun’s core or center is very hot.

Temperatures can reach about 15 million degrees Celsius, high enough for nuclear fusion to occur.

• There is also tremendous pressure at the core.

• Nuclear fusion only occurs under conditions of extremely high temperature and pressure.

Layers of the Sun

Layers of the Sun• The sun’s atmosphere has three layers:

the photosphere, the chromosphere, and the corona.

• The photosphere is the inner layer. Photo means “light”, so photosphere means the sphere that makes light

• The chromosphere is the middle layer. Chrom means “color”, so the chromosphere is the “color sphere”

The Corona• The outer layer that looks like a white

halo around the sun is called the corona. Corona means “crown”. This is only visible during eclipses or from special telescopes.

• The corona sends out a stream of electrically charged particles called solar wind. This is what causes the auroras at the poles of the Earth.

During a SolarEclipse, the corona is visible

Photo by Luc Viatour

Aurora Borealis or “Northern Lights”

http://onemansblog.com/wp-content/uploads/2007/03/AuroraBorealis.jpg

• From space, the aurora is a crown of light that circles each of Earth’s poles. The IMAGE satellite captured this view of the aurora australis (southern lights) on September 11, 2005, four days after a record-setting solar flare sent plasma—an ionized gas of protons and electrons—flying towards the Earth. The ring of light that the solar storm generated over Antarctica glows green in the ultraviolet part of the spectrum,

Layers of the Sun

Surface of the Sun• Features on or above the sun’s surface

include sunspots, prominences, and solar flares.

• Sunspots are areas of gas on the sun that are cooler than the gases around them. Cooler gases don’t give off as much light as hotter gases, which is why sunspots look darker than the rest of the photosphere.

Surface of the Sun• Sunspots usually occur in pairs or

groups.

• Reddish loops of gas called prominences link different parts of sunspot regions.

• Prominences are about the same temperature as the chromosphere, about 10,000 degrees Celsius

Solar Prominence

http://www.uwmc.uwc.edu/astronomy/images/equinoxprom_eit.jpg

Surface of the Sun• When the loops in sunspot regions

suddenly connect they release large amounts of energy. This creates explosions called solar flares.

• Solar flares can increase solar wind from the corona and this can result in particles affecting the upper atmosphere of Earth causing magnetic storms.

Solar Flare

http://www.daviddarling.info/images/solar_flare.jpg

Surface of the Sun• Magnetic storms can disrupt radio,

telephone and television signals.

http://wpcontent.answers.com/wikipedia/commons/thumb/f/f3/Magnetosphere_rendition.jpg/400px-Magnetosphere_rendition.jpg

Aurora Borealis

Image from http://farm1.static.flickr.com/186/415105440_bd3975ca0f.jpg?v=0

Credits• Top right cover image

http://images.google.com/imgres?imgurl=http://www.swpc.noaa.gov/primer/primer_graphics/Sun.png&imgrefurl=http://www.sec.noaa.gov/primer/primer.html&usg=__Qc6ejh8rvAQnzmHBiKWyodETH48=&h=564&w=634&sz=224&hl=en&start=4&sig2=WtRUngAf8FEql8twLupd9g&tbnid=t_MlFPDborvBhM:&tbnh=122&tbnw=137&prev=/images%3Fq%3Dsun%26gbv%3D2%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DG&ei=Ch7zSe6jK6PDtgfBy8yyDw

• Top left cover image http://tbn2.google.com/images?q=tbn:PhuKcXZ3aSSqOM:http://z.about.com/d/space/1/5/Y/Q/sun_tour.jpg

• Sun’s Layers diagram http://www.ifa.hawaii.edu/%7Ebarnes/ast110_06/tsaas/1003b.jpg

• Aurora Australis on South Pole http: //www.ufoarea.com/pictures/aurora_australis.jpg

• Aurora Australis info http://www.ufoarea.com/universe_nasa_australis.html• Solar Eclipse photo by Luc Viatour found at

http://i181.photobucket.com/albums/x176/weirdscience_photos/SolarEclipse1999.jpg