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Welcome! Sun and Seasons Photo from 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. What are we going to cover

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Sun and Seasons

Photo from

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.

what are we going to cover
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

the sun
The Sun
  • Is a star
  • Made of gases
  • Is our primary source of energy

70% hydrogen and 28% helium

Light (radiation)

Image at

how big is the sun
How Big is the Sun?

Activity: Let’s measure the Sun

how big is the sun5
How Big is the Sun?

About 110 times wider than Earth


1.3 million times bigger than Earth

Photo from

how does our sun compare to other stars
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

so is our sun an average star
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


High cadence solar rotation, EIT 195Š(Dec. 10-24, 1999) Movie at

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”

sun s magnetic field
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

inside the sun
Inside the Sun
  • Core
  • Radiative Zone
  • Convection zone

Image at

the sun s atmosphere
The Sun’s Atmosphere
  • Photosphere
  • Chromosphere
  • Corona

Photosphere image:

Chromosphere image:

Corona image:

energy from the sun
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

features in the photosphere
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

more on sunspots
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 and

solar events
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)

solar wind
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

  • 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

coronal mass ejection
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

cme s effects on earth
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.

  • Let’s go observe the Sun
  • Sunspot graphing
influences on earth
Influences on Earth
  • Gravity
  • Light (Radiation)
  • Solar Wind (already discussed)
  • Orbits
    • The Sun’s powerful gravity keeps the planets in orbit
  • 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 and


activities on sunlight
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
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


sunlight is absorbed by earth
Sunlight is absorbed by Earth

Let’s test what happens to the light.

Activity Time!!

sunlight is absorbed by earth27
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
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

sun as a source of energy29
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 and

young stars form in nebulae from small magellanic cloud
Young stars form in nebulaefrom Small Magellanic Cloud

Image at


Star-forming region in the Large Magellanic Cloud:


Orion image at

our sun is a regular small star
Our Sun is a Regular/ Small Star

Image at

in a few billion years red giant
In a few Billion years… Red Giant

Image at

our sun s habitable zone
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

by 5 billion years white dwarf
By 5 billion years… White Dwarf

Image at


Image at


Image at

massive stars are different
Massive Stars are different

Image from


Image from

supernova massive star explodes
Supernova—Massive Star Explodes

Images at

done with the sun
Done with the Sun
  • Time for Seasons!