The Sun

Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html

The Sun

• Is a star

• Made of gases

• Is our primary source of energy

70% hydrogen and 28% helium

Light (radiation)

Image at http://science.nasa.gov/headlines/y2007/images/chromosphere/LimbFlareJan12_strip2.jpg

How Big is the Sun?

About 110 times wider than Earth

Or

1.3 million times bigger than Earth

Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html

How does our Sun compare to other Stars?

• Active stars range in size from supergiants to dwarfs

• Stars range from very bright (supergiants) to very dim (dwarfs)

• Stars range from very hot blue on the outside (O class) to cool red on the outside (M class)

Our Sun is in-between--yellow

Our Sun is a dwarf—medium mass

Our Sun is a medium-bright dwarf

Rotation

At the equator, the Sun rotates once every 25.4 days

Near its poles, the Sun rotates once every 36 days

Known as “differential rotation”

Energy from the Sun

• Nuclear chain reaction (hydrogen forming helium)

• Releases radiation (gamma rays)

• The gamma ray loses energy as it bounces around inside the Sun

• It is finally released at the photosphere, primarily as visible light

Image at http://solarscience.msfc.nasa.gov/interior.shtml

Inside the Sun

• Core

• Radiative Zone

• Convection zone

Image at http://solarscience.msfc.nasa.gov/interior.shtml

The Sun’s Atmosphere

• Photosphere

• Chromosphere

• CoronaPhotosphere image: http://science.msfc.nasa.gov/ssl/pad/solar/surface.htm Chromosphere image: http://science.msfc.nasa.gov/ssl/pad/solar/chromos.htm Corona image: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=191

The Photosphere

• Photosphere: The ‘Surface’ of the Sun, and the layer from which light is given off

• Sunspots: areas of the sun that look dark due to being cooler

Chromosphere & Corona

• Chromosphere: middle layer of the Sun’s atmosphere

• Corona: Largest layer of the Sun’s atmosphere

Solar Wind• Blows charged particles and magnetic fields away from the

Sun• Charged particles captured by Earth’s magnetic field• Create Auroras or Northern and Southern Lights

Image at http://solarscience.msfc.nasa.gov/the_key.shtml

Coronal Mass EjectionCMEs: large amount of electrically-charged gas are ejected suddenly from the Sun’s corona

CMEs can damage satellites and interfere with radio and power distribution equipment

Prominences and Flares• Prominences- huge arching columns of gas• Flares: when gases near a sunspot brighten

shooting outward

Radiation• Our Sun (and all active stars) emits radiation

– Radio, infrared, visible, ultraviolet, x-ray and even some gamma rays

– Most of the sunlight is yellow-green visible light or close to it

The Sun at X-ray wavelengths

Image and info at http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html and

http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/sun.html

.

Sun as a Source of Energy• Light from the Sun is absorbed by the Earth,

unevenly to:– drive wind bands – which drive surface currents– drive deep ocean currents– drive water cycle – drive weather

NASA image at http://visibleearth.nasa.gov/view_rec.php?id=107 Credit: NASA GSFC Water and Energy Cycle http://www.nasa.gov/centers/jpl/news/grace-20061212.html

Our Sun is a Regular/ Small Star

Image at http://www.gsfc.nasa.gov/topstory/20011210insidesun.html

Stars begin as a cloud of gas

and dust called

nebula

Image at http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/

Main Sequence

Image at http://hubblesite.org/newscenter/archive/releases/1997/26/image/a/

Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star

• After billions of years a Main sequence star will turn into a Red Giant

By 5 billion years… White Dwarf:This happens when all that is left is the hot

dense core

Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/

Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2000/28/image/a/format/web_print/results/50/

Supergiant's and SupernovasSupergiant's: Extremely large (and unstable red giants

Supernovas: The explosion that occurs when the supergiant’s core collapses

Black Hole• If the remaining dense core from a supernova

collapses to a point• The gravity from this point is so strong that

nothing can escape from it not even light.– If you were to shine a light into a black hole

the light would simply disappear

Life of a Star