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Sun and Seasons

Created by the Lunar and Planetary InstituteFor Educational Use OnlyLPI 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?

Activity: Let’s measure the Sun

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 daysNear its poles, the Sun rotates once every 36 daysKnown 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 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/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

Activities• Let’s go observe the Sun• Sunspot graphing

Influences on Earth

• Gravity• Light (Radiation)• Solar Wind (already

discussed)

Gravity

• Orbits– The Sun’s powerful gravity

keeps the planets in orbit

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 andhttp://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 EarthLet’s test what happens to the light.

Activity Time!!

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 nebulaefrom 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 ZoneBillions 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/

Done with the Sun• Time for Seasons!