Transcript The Sun

The Sun
On-line Lesson
On-line Lessons: The Sun
 What is the Sun ?
On-line Lessons: The Sun
• Another planet ?
• A star ?
• Or a galaxy ?
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
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% ?
On-line Lessons: The Sun
The Sun's outer visible layer is called the
photosphere and has a temperature of 6,000°C
(11,000°F). This layer has a mottled appearance
due to the turbulent
eruptions of energy
at the surface.
(see “Views of Solar System”
in the Links)
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.
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 !!!!!!!!!
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)
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)
On-line Lessons: The Sun
How can we observe the Sun’s 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.
On-line Lessons: The Sun
 The Sunspots above all other features give us
the opportunity to study the Sun’s Rotation
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)
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 it’s 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.