The Sun

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The Sun

• On-line Lesson

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On-line Lessons The Sun

• What is the Sun ?

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On-line Lessons The Sun

• Another planet ?
• A star ?
• Or a galaxy ?

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On-line Lessons The Sun

• Well, the Sun is a Star and it is the largest
• object in our Solar System Sun 9 planets
• (see The Nine Planets in the Links)
• Sun

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On-line Lessons The Sun

• A list of the mass distribution within our
• Solar System
• Sun 99.85 of all the matter in the Solar
  System
• Planets 0.135 condensed out of the same disk of
  
• material that
  formed the Sun
• Comets 0.01 ?
• Satellites 0.00005
• Minor Planets 0.0000002 ?
• Meteoroids 0.0000001 ?
• Interplanetary Medium 0.0000001 ?

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On-line Lessons The Sun

• The Sun's outer visible layer is called the
• photosphere and has a temperature of 6,000C
• (11,000F). This layer has a mottled appearance
• due to the turbulent
• eruptions of energy
• at the surface.
• (see Views of Solar System
• in the Links)

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On-line Lessons The Sun

• What is the age of the Sun ?
• Well, the Sun has been active for 4.6 billion
  years and has
• enough fuel to go on for another five billion
  years or so.
• What will happen then ?
• The Sun will start to fuse helium into heavier
  elements and
• begin to swell up, ultimately growing so large
  that it will
• swallow the Earth. After a billion years as a
  Red Giant,
• it will suddenly collapse into a White Dwarf --
  the final end
• product of a star like ours.
• It may take a trillion years to cool off
  completely.

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On-line Lessons The Sun

• How heavy is the Sun ?
• The Sun is 332,830 times heavier than the Earth
  !!!
• What does this mean in kilos ?
• The mass of the Sun is
• 1,98 x
• This is a really huge number !!!!!!!!!

10000000000000000000000000000000 kg
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On-line Lessons The Sun

• Is the Sun the only such object around ?
• Not really, it is one of about 100 billion
  similar objects in the
• Milky Way (see The Virtual Amateur Astronomer,
  VI section, in the Links)

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On-line Lessons The Sun

• The Earth rotates around its axis and the Sun.
  Does the Sun rotate, too ?
• The Sun like the planets rotates around its axis
  in an anti-clockwise direction when viewed
  looking down from above its North Pole. For an
  observer at Earth the rotation is from left to
  right, i.e., features move from the Eastern limb
  towards the Western.
• (see Windows to the Universe in the Links)
  

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On-line Lessons The Sun

• How can we observe the Suns Rotation ?
• On the surface of the Sun there are dark spots,
  some as large as 50,000 miles in diameter, moving
  across the surface, contracting and expanding as
  they go. These strange and powerful phenomena are
  known as sunspots.

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On-line Lessons The Sun

• The Sunspots above all other features give us the
  opportunity to study the Suns Rotation

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On-line Lessons The Sun

• The spots are carried along with the rotation of
  the Sun and therefore by measuring their motion
  it is possible to measure the rotation period of
  the Sun. (see On-Line lessons in the
  EUDOXOS website)

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On-line Lessons The Sun

• At this point we need to notice that while the
  Earth rotates around the Sun at the same time the
  Sun rotates around its axis, so the period we
  observe from Earth is slightly larger than the
  true period, which we would observe if we were
  viewing the Sun from a distant star.
• In addition, the Sun is not a solid body like the
  Earth, and unlike the Earth its made up of hot
  gas, and therefore it exhibits differential
  rotation. That means that the rotation period can
  vary with latitude and depth.In the photosphere,
  it varies from 25 days on the equator to more
  than 30 days at 60 degrees latitude.