Download The Sun - Sophia

Part 6:The Sun
Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html
The Sun
• Is a star
• Made of gases
70% hydrogen and 28% helium
• Is our primary
source of energy
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
•Even a mediumsized sunspot is
as big as the
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 a dwarf—medium
mass
Our Sun is a medium-bright
dwarf
Our Sun is in-between--yellow
So is our Sun an average star?
• No—most stars are smaller and cooler than our Sun
BUT
• Most of the bright stars we see are bigger and hotter
The Sun rotates at different speeds…
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”
Click for movie
Sun’s Magnetic Field
• Winds up due to differential rotation
• Eventually forms loops and becomes tangled
Inside the Sun
• Core
• Radiative Zone
• Convection zone
Image at http://solarscience.msfc.nasa.gov/interior.shtml
The Sun’s Atmosphere
• Photosphere
– Most of the sunlight we see
is from here. The sun’s
surface
• Chromosphere
– Just above the photosphere
– It is a thin layer that
appears red in color
• Corona
– The Sun’s atmosphere
Energy from the Sun
•
Nuclear fusion reaction (hydrogen fusing
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
Features in the Photosphere
• Sunspots
– Dark and small (but brighter than Full Moon and big
as Earth)
– Cool-- temperatures only 6,200 F (Sun’s surface is
10,000 F)
– Associated with magnetic fields: one set of spots is
positive, other is negative
Image at http://sohowww.nascom.nasa.gov/gallery/top10/top10_results.html
More on Sunspots
• Our Sun has an activity cycle of
11 years
• Sunspots appear at specific
latitudes on Sun
– Bands of latitude move towards
equator during cycle
Images at
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/q
uestion17.html and
http://solarscience.msfc.nasa.gov/SunspotCycle.shtml
Solar Events
• Flares (Explosions of energy on the
surface of the Sun)
• Prominences: cloudlike gases looping
above the sun
• Coronal Mass Ejections (massive clouds
of plasma ejected from the Sun)
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
Auroras
• Electrons from solar wind are captured by the Earth’s magnetic field
• Interact with atoms in our atmosphere: oxygen and nitrogen make red
and green; nitrogen can also make violet
• Northern lights are Aurora Borealis, while southern are Aurora Australis
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’s Radiation at Earth
• The Earth’s atmosphere filters out some frequencies
– Ozone layer protects us from some ultra-violet, and most xrays and gamma rays
– Water and oxygen absorb some radio waves
– Water vapor, carbon dioxide, and ozone absorbs some
infrared
Electromagnetic spectrum
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/what_is_ir.html
.
Young
stars form
in nebulae
from Small
Magellanic Cloud
Image at
http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/
Star-forming region in the Large Magellanic Cloud:
http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
Our Sun is a Regular/ Small Star
Image at http://www.gsfc.nasa.gov/topstory/20011210insidesun.html
By 5 billion years… White Dwarf
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/
Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2004/27/image/a/format/large_web/results/50/
Massive
Stars are
different
Image from
http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/
Betelgeuse
Image from http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/
Supernova—Massive Star Explodes
Images at
http://hubblesite.org/newscenter/archive/releases/star/supernova/2004/09/results/50/
http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/
http://chandra.harvard.edu/photo/2009/casa/