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Sun and Seasons
Created by the Lunar and Planetary InstituteFor Educational Use Only
LPI is not responsible for the ways in which this powerpoint may be used or altered.
Photo from http://sohowww.nascom.nasa.gov/bestofsoho/bestofsoho.html
What are we going to cover
• Properties of the Sun• Influence on Earth:
– Gravity– Light– Solar wind
• Life cycle of the Sun• Seasons
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
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
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”
High cadence solar rotation, EIT 195Š(Dec. 10-24, 1999) Movie at http://sohowww.nascom.nasa.gov/bestofsoho/Movies/EITdec99/EITdec99sm.mpg
Sun’s Magnetic Field• Winds up due to differential rotation• Eventually forms loops and becomes tangled
Animation of how the Sun's magnetic field winds up and loops out. Movie at http://sohowww.nascom.nasa.gov/bestofsoho/Movies/dynamo/dynamosm.mpg
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
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
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 negativeImage 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/question17.html
and http://solarscience.msfc.nasa.gov/SunspotCycle.shtml
Solar Events
• Flares (Explosions of energy on the surface of the Sun)
• Prominences• Coronal Mass Ejections (massive clouds of
plasma ejected from the Sun)
Movie: Six months with EIT 171 (Aug. 12, 2003 - Feb. 9, 2004) http://sohowww.nascom.nasa.gov/bestofsoho/Movies/171/EIT171sm.mpg
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
Animation of solar wind impacting the magnetosphere and creating aurora http://sohowww.nascom.nasa.gov/bestofsoho/Movies/animation/Solarwind.mpg
Coronal Mass Ejection
The eruption of a huge bubble of hot gas from the Sun
This series of images of coronal mass ejections taken with LASCO C3 (May 1-31, 1997) at http://sohowww.nascom.nasa.gov/bestofsoho/Movies/C3May97/C3May97sm.mpg
CME’s effects on Earth• Can damage satellites• Very dangerous to astronauts• Power problems
Animation of a CME leaving the Sun, slamming into our magnetosphere. http://sohowww.nascom.nasa.gov/bestofsoho/Movies/recon/reconsm.mpg
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
.
Activities on Sunlight
• UV Man (or woman, or dog, bug, etc.)• Observations of infrared light using filters and
cell phones
Sun’s Radiation at Earth
• The Earth’s atmosphere filters out some frequencies– Ozone layer protects us from some ultra-violet, and
most x-rays 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
.
Sunlight is absorbed by Earth
• The Sun does NOT send “heat rays” into space. Some of its light is infrared, but that is not the same thing as heat.
• The Sun’s light is absorbed by Earth (clouds, plants, oceans, rock…)
• By absorbing the light, we are transforming it into heat energy
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
Sun as a Source of Energy
• Plants need light for photosynthesis• Without its heat, the only inhabitable areas on
Earth would be near volcanic vents
Images from http://nasadaacs.eos.nasa.gov/articles/2005/2005_rainforest.html and http://planetquest.jpl.nasa.gov/TPF/tpf_book/gallery/4-2a.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
In a few Billion years… Red Giant
Image at http://hubblesite.org/newscenter/archive/releases/1997/26/image/a/
Our Sun’s Habitable Zone
Billions of years ago, things may have been different– The Sun was cooler (by up to
30%!)– Earth’s atmosphere was
different (thicker, carbon dioxide)
• Conditions will be different in the future– By many accounts, increases
in the Sun’s temperature will make Earth uninhabitable in 1 billion years or less
– These changes will also affect other planets… Mars?
Animation at http://www.nasa.gov/97994main_BHabitableZone.MPG
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/