Planetary Motion

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Planetary Motion
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Planetary Motion
A Revolution in Astronomy

• Each planet spins on its axis. The spinning of
  a body, such as a planet, on its axis is called
  rotation.
• The orbit is the path that a body follows as it
  travels around another body in space.
• A revolution is one complete trip along an
  orbit.

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Planetary Motion
A Revolution in Astronomy

• When Earth completes one FULL rotation around
  its axis, what have we experienced? How long
  does this take?
• What Earth completes one FULL revolution around
  the sun, what have we experienced? How long does
  this take?

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Earths Rotation and Revolution
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Planetary Motion
A Revolution in Astronomy, continued

• Johannes Kepler made careful observations of the
  planets that led to important discoveries about
  planetary motion in the early 1600s.
• Keplers First Law of Motion Kepler discovered
  that the planets move around the sun in
  elliptical orbits.
• What type of model is this???
• Heliocentric model

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Planetary Motion
A Revolution in Astronomy, continued

• Keplers Second Law of Motion Kepler noted that
  the planets seemed to move faster when they are
  close to the sun and slower when they are farther
  away.
• Keplers Third Law of Motion Kepler observed
  that planets more distant from the sun, such as
  Saturn, take longer to orbit the sun.

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Planetary Motion
Newton to the Rescue!

• Kepler did not understand what causes the
  planets farther from the sun to move slower than
  the closer planets.
• Sir Isaac Newtons description of gravity
  provides an answer.

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Planetary Motion
Newton to the Rescue! continued

• The Law of Universal Gravitation Newtons law
  of universal gravitation states that the force of
  gravity depends on the product of the masses of
  the objects divided by the square of the distance
  between the objects.
• According to this law, if two objects are moved
  farther apart, there will be less gravitational
  attraction between them.

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Our Solar System
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Our Solar System
Our Solar System

• Our solar system includes the sun, the planets,
  and many smaller objects.

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Our Solar System
Measuring and Interplanetary Distances
Scientists use the astronomical unit to measure
distances in space. One astronomical unit is the
average distance between the sun and Earth, or
approximately 150,000,000 km (or 93,205,678.8
miles)
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Our Solar System
The Inner and Outer Solar Systems

• The Inner Planets The planets closest to the sun
  include Mercury, Venus, Earth, and Mars.
• The Outer Planets The outer planets include
  Jupiter, Saturn, Uranus, and Neptune.

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• The Inner Planets The planets closest to the sun
  include Mercury, Venus, Earth, and Mars.

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• The Outer Planets The outer planets include
  Jupiter, Saturn, Uranus, and Neptune.

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The Inner Planets
Mercury Closest to the Sun

• Mercury is a very hot, small planet. It only
  takes Mercury 88 days to revolve around the sun.

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The Inner Planets
Venus Earths Twin?

• The Atmosphere of Venus Of all the inner
  planets, Venus has the densest atmosphere.
• Mapping Venuss Surface The Magellan spacecraft
  mapped the surface of Venus by using radar waves.

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The Inner Planets
Earth An Oasis in Space

• Water on Earth Earth is warm enough to keep most
  of its water from freezing and cool enough to
  keep its water from boiling away. Liquid water is
  important to life on Earth.
• The Earth from SpaceSatellites are used
  tostudy the Earth fromspace in order to
  betterunderstand global systems.

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The Inner Planets
Mars Our Intriguing Neighbor

• The Atmosphere of Mars Mars has a thin
  atmosphere with low air pressure.
• Water on Mars Liquid water cannot exist on
  Marss surface today, but most likely it was
  there in the past.

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The Inner Planets
Mars Our Intriguing Neighbor, continued

• Where Is the Water Now? Mars has two polar
  icecaps made of frozen water and carbon dioxide.
  Many scientists think that there is more frozen
  water beneath the Martian soil
• Martian Volcanoes Mars has two large volcanic
  systems, one of which includes the largest
  mountain in the solar system.

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The Inner Planets
Mars Our Intriguing Neighbor, continued

• Missions to Mars Several recent missions to Mars
  were launched to gain a better understanding of
  the planet.

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The Outer Planets
Jupiter A Giant Among Giants

• Jumbo Sized Jupiter is the largest planet in our
  solar system.
• NASA Missions to Jupiter NASA has sent five
  missions to Jupiter to study Jupiters atmosphere
  and moons.

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The Outer Planets
Saturn Still Forming

• The Rings of Jupiter Saturns rings are the
  largest of all of the gas giants rings.
• NASA Exploration of Saturn Launched in 1997, the
  Cassini spacecraft is designed to study Saturns
  rings, moon, and atmosphere.

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The Outer Planets
Uranus A Small Giant

• Uranuss Atmosphere The atmosphere of Uranus is
  mainly hydrogen and methane, which makes the
  planet appear to be blue-green in color.

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The Outer Planets
Uranus A Small Giant, continued

• A Tilted Planet Unlike most other planets,
  Uranus is tipped over on its axis. So its axis of
  rotation is tilted by almost 90 and lies almost
  in the plane of its orbit.

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The Outer Planets
Neptune The Blue World

• Discovery of Neptune Neptune was not discovered
  until 1846.
• The Atmosphere of Neptune The composition of
  Neptunes atmosphere is similar to that of
  Uranuss atmosphere, but Neptune has belts of
  clouds that are much more visible.

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The Outer Planets
Pluto A Dwarf Planet

• A Small World Pluto is less than half the size
  of Mercury.
• Reclassified Since its
  discovery in 1930, Pluto
  has been called the ninth
  planet. However, in
  2006, it
  was reclassified as a
  dwarf planet.
• A dwarf planet is any object that orbits the sun,
  is round because of its own gravity, but has not
  cleared its orbital path.

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• "Hasn't cleared its orbital path" means that in
  Pluto's orbital space there are other objects
  still there.
• Planets have cleared their orbital path of debris
  and small objects, but Pluto orbits within the
  Kuiper Belt, a region filled with millions of
  small objects.