THE SUN: AWESOME AND ACTIVE

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THE SUN AWESOME AND ACTIVE

• Boston University PHOTON
• Outreach Presentation

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The Sun

• An average-size yellow star, just like billions
  of others in the universe
• Center of the solar system, Earth orbits around
  it
• Formed about 4.6 billion years ago
• The sun has a mass of 2x1030 kg or 330,000
  Earths, thats 99.8 of the mass in the solar
  system.

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The Suns Energy Earth

• The Sun is the source of all of the energy on
  Earth.
• The amount of energy that reaches Earth from the
  Sun in one second is enough energy to meet
  Massachusetts current energy needs for
  32,655,294 years!!!
• About half the energy that hits the Earth is
  absorbed and used to heat the planet.
• You can feel this energy in the form of heat on
  your skin on a sunny day.

figure based on data from California Energy
Commision http//www.energy.ca.gov/electricity/us
_percapita_electricity_2003.html
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Where does the Suns Energy Come From?

• Energy is produced in the Suns core through a
  process known as nuclear fusion.
• Nuclear fusion is when nuclei of one kind of
  element combine to make a new nucleus in that
  requires less energy to hold it together. This
  difference in energy is spit out as a result of
  the reaction.
• The Suns nuclear fusion occurs when four
  hydrogen nuclei combine to make helium and
  release energy.
• This type of reaction cant happen just
  anywhere, it can only happen at incredibly high
  temperatures and pressures like those found in
  stars, somewhere around 23 million degrees!!

Energy
1 Helium nucleus
4 Hydrogen nuclei
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How much energy does the Sun make?

• We know how much energy the Sun emits by
  measuring the amount of energy that reaches
  Earth.
• The Sun consumes 660 million tons of hydrogen
  releasing 100 billion megatons of energy per
  second! Thats the same energy as 20 billion
  Hydrogen bombs every second!
• Based on the amount of hydrogen the Sun consumes
  per second and the mass of the Sun, we estimate
  its lifetime to be 50 billion years.

Nuclear Fusion Hydrogen Bomb50 megatons
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Whats inside the sun?
Layers of the Sun 1. Core the core of the sun
alone is the size of 13 Earths! 2. Radiative
Zone energy from the core radiates through this
part of the Sun 3. Convective Layer convection
cells move energy through this part of the
Sun 4. Photosphere This is the part of the sun we
see 5. Chromosphere a part of the Suns
atmosphere 6. Corona This is a bright halo
around the Sun
Diameter of the Sun Diameter of 56 Earths!
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Energy Escapes the Sun

• Fusion occurs in the Suns core, the hottest
  part.
• The energy released by the fusion in the Suns
  core is in the form of light.
• It only takes 8 minutes for light from the
  surface of the Sun to reach Earth
• But it takes 170,000 for the light energy from
  the core to reach the Suns surface because it
  doesnt go in a straight line

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The Changing Sun

• The surface of the Sun is constantly changing
• The Sun is shooting particles off it all the time
  called the Solar Wind
• There is an 11-year Solar Cycle when the Sun
  goes from being very active (solar maximum) to
  not not very active (solar minimum

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How is the Sun active?

• The solar cycle is characterized by the rising
  and falling of solar activity
• The solar maximum is the period of greatest solar
  activity
• During solar maximum the Sun is more active
  meaning there are more sunspots and solar flares

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Sunspots

• What?
• Dark spots on the Sun's surface that are cooler
  than the surrounding areas
• Temperature of
• Sunspot 3800 K
• Surrounding area 5800 K
• Why?
• The strong magnetic field in that area stops the
  area from being able to transfer energy so the
  temperature isnt as high

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More about Sunspots

• Sunspots can be about the size of Earth or even
  bigger!!!
• They come in pairs
• They are still really hot, just not as hot as the
  rest of the Suns surface
• Sunspots move across Suns surface as it rotates

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Magnetic Activity on the Sun

• Sunspots are caused by strong magnetic fields
• Magnetic ropes break through the Suns surface
• At each end of the rope is a sunspot
• It is the Suns magnetic activity that causes
  solar storms and solar flares

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How do we know all of this about the Sun?

• Telescopes
• You can look at the Sun through a telescope with
  special filters.
• You can also use a solar telescope that projects
  the image of the Sun onto a piece of paper
  instead of into your eye.
• Satellites
• There are also several spacecraft that
• are observing the Sun SOHO, TRACE, STEREO
• These satellites look at the Sun in all
• different kinds of light (ultraviolet, visible,
• infrared, X-ray) to see everything that is
• going on
• Many cameras on telescopes need to use
• a caronagraph, where a disk is used to block
• out the Suns surface so we can see all the dim
• stuff that the Suns brightness would drown out