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Sun and Seasons

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

Created by the Lunar and Planetary Institute

For Educational Use Only

LPI is not responsible for the ways in which this powerpoint may be used or altered.

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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

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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

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How Big is the Sun?

Activity: Let’s measure the Sun

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How Big is the Sun?

About 110 times wider than Earth


1.3 million times bigger than Earth

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

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How does our Sun compare to other Stars?

Our Sun is a dwarf—medium mass

  • 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 medium-bright dwarf

Our Sun is in-between--yellow

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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

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High cadence solar rotation, EIT 195Š(Dec. 10-24, 1999) Movie at http://sohowww.nascom.nasa.gov/bestofsoho/Movies/EITdec99/EITdec99sm.mpg

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”

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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

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Inside the Sun

  • Core

  • Radiative Zone

  • Convection zone

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

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The Sun’s Atmosphere

  • Photosphere

  • Chromosphere

  • Corona

Photosphere 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

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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

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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

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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 andhttp://solarscience.msfc.nasa.gov/SunspotCycle.shtml

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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

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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

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  • 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 aurorahttp://sohowww.nascom.nasa.gov/bestofsoho/Movies/animation/Solarwind.mpg

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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

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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.


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  • Let’s go observe the Sun

  • Sunspot graphing

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Influences on Earth

  • Gravity

  • Light (Radiation)

  • Solar Wind (already discussed)

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  • Orbits

    • The Sun’s powerful gravity keeps the planets in orbit

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  • 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



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Activities on Sunlight

  • UV Man (or woman, or dog, bug, etc.)

  • Observations of infrared light using filters and cell phones

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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



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Sunlight is absorbed by Earth

Let’s test what happens to the light.

Activity Time!!

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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

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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

Credit: NASA GSFC Water and Energy Cycle


NASA image at http://visibleearth.nasa.gov/view_rec.php?id=107

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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

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Young stars form in nebulaefrom Small Magellanic Cloud

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

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Star-forming region in the Large Magellanic Cloud: http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/

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Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/

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Our Sun is a Regular/ Small Star

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

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In a few Billion years… Red Giant

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

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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

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    By 5 billion years… White Dwarf

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

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

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    Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2004/27/image/a/format/large_web/results/50/

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    Massive Stars are different

    Image from http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/

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    Image from http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/

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    Supernova—Massive Star Explodes

    Images at



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    Done with the Sun

    • Time for Seasons!