11.2 The Sun and the Planets

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11.2 The Sun and the Planets
See pages 382 - 383

• Our Sun, an average star in the universe, is the
  center of our solar system.
• Our solar system is full of planets, moons,
  asteroids and comets, all of which revolve around
  the Sun at the center.
• When a star forms from a nebula, gravity pulls
  most of the material into the new star, but some
  may also clump together to form objects in a
  solar system.
• A planet is a celestial body that orbits one or
  more stars.
• Each planet may also spin on its axis (rotates)
  while it orbits the Sun (revolves).
• Our solar system formed approximately 4.5 billion
  years ago.
• The four inner (rocky) planets formed in the
  first 100 million years on the Suns existence,
  while the outer (gas) planets formed later from
  the remnants of the Suns original nebula.

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The Sun
See pages 383 - 384

• contains 99 of all the mass found in our solar
  system.
• has a diameter equal to 110 Earths.
• made up mostly of hydrogen.
• has no solid surface
• has distinctive features such as sun spots,
  flares, and prominences.

The hydrogen molecules -are forced to join
together through massive gravity -form new helium
molecules, then -release huge quantities of
energy as light and heat through the process of
thermonuclear fusion.
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Solar Winds
See page 385

• Sometimes, gases from the Suns corona erupt
  outwards like a bursting soap bubble.

1. The resulting solar wind is full of high-energy
   particles that would kill any life on Earth they
   struck.
2. Luckily, our magnetic field deflects this solar
   wind. We can see these particles being deflected
   when we see the Northern Lights.
3. Large outbursts of solar winds can wreak havoc
   with satellites as well as Earth-bound energy
   supplies such as power plants.

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The Planets
See pages 385 - 387

• 1)To be considered a planet, a body must
• orbit one or more stars,
• be large enough that its own gravity holds it in
  a spherical shape, and
• be the only body occupying the orbital path.
• 2) Distances between planets in the solar system
  are measured in astronomical units (AU).
• -One AU the average distance from the Sun to
  the Earth.
• The inner planets are relatively close to the
  center of the solar system
• Mars is 1.52 AU from the Sun.
• The next planet, Jupiter, an outer planet, is
  5.27 AU from the Sun.
• The most distant planet, Neptune, is 30.06 AU
  from the Sun.

Inner, rocky planets Inner, rocky planets Outer, gaseous planets Outer, gaseous planets
Mercury Smallest planet Jupiter Largest planet
Venus Earths sister Saturn Rings many moons
Earth Only life in universe Uranus Methane gas planet
Mars The red planet Neptune Outermost planet
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Other Solar System Bodies
See pages 388 - 389

• There are also numerous celestial bodies
  smaller than planets in our solar system. Moons
  are found around all planets except Mercury and
  Venus.

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Asteroids are found mostly between Mars and
Jupiter in the asteroid belt. It is thought these
are leftovers from the formation of the solar
system.
This picture of the rocky asteroid 951 Gaspra was
taken by NASA's Galileo spacecraft. Image
Credit NASA
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The Kuiper Belt is a disk-shaped region past the
orbit of Neptune, roughly 4,400,000,000 to
14,900,000,000 km (30 to 100 AU) from the Sun,
that consists mainly of small bodies which are
the remnants from the Solar System's formation.
It also contains at least one dwarf planet -
Pluto. Pluto is indeed now considered to be a
member of the Kuiper Belt - the largest object
belonging to it, in fact! Like other members of
the Belt, it is composed primarily of rock and
ice and is relatively small.. The Kuiper Belt is
also believed to be the source for short-period
comets (ie, those that take less than 200 years
or orbit).
http//heasarc.gsfc.nasa.gov/docs/cosmic/solar_sys
tem_info.html
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Comets (sometimes called dirty snowballs) are
actually rocky travelers, following huge
orbits far outside the planets in the Oort Cloud.
Trans-neptunian objects refer to objects
outside Neptunes orbit, including ex-planet
Pluto (now referred to as a dwarf planet). These
objects orbit the Sun in a large area known as
the Kuiper Belt.
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The Oort Cloud In 1950, astronomer Jan Oort
proposed that long-period comets reside in a vast
spherical cloud residing 50,000 to 50,000 AU
from the Sun, at the outer reaches of the Solar
System. This major reservoir of comets has come
to be known as the Oort Cloud.
The Kuiper belt can be described as disc or
doughnut-shaped, but the Oort cloud is more like
a very thick "bubble" that surrounds the entire
solar system, reaching about half-way from the
Sun to the next nearest star. Statistics imply
that it may contain as many as a trillion (1012)
comets. Unfortunately, since the individual
comets are so small and at such large distances,
we have no direct evidence for the Oort Cloud.
The Oort Cloud is, however the best theory to
explain how long-period comets exist.
http//heasarc.gsfc.nasa.gov/docs/cosmic/solar_sys
tem_info.html
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The Oort Cloud is at the farthest reaches of the
Suns gravitational pull, almost 25 of the way
to the next nearest star, Proxima Centauri.
https//www.youtube.com/watch?vZDaFQsdNNgU
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http//herschel.jpl.nasa.gov/solarSystem.shtml
Artists rendering of the Kuiper Belt and Oort
Cloud.
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