The Solar System

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The Solar System
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Ch. 20.1 Observing the Solar System

• Objective
• Explain how the heliocentric and geocentric
  models of the solar system differ.
• Explain how the observations and view of
  scientists such as Kepler and Copernicus
  contributed to the current understanding of the
  solar system.
• Identify and explain the two factors that keep
  planets in their orbits.

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Engage and Explore

• Where was the sun when this picture was taken?

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Wandering Stars

• The ancient Greeks noticed that five points of
  light seemed to wander among the stars.
• The Greeks called these planets from the word
  meaning wandering star.

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Greek Idea Earth at the Center

• Aristotle, a Greek scientist, believed that the
  universe is perfect and finite and that Earth is
  stationary at its center.

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Greek Ideas Earth at the Center

• Aristotle believed that the Earth was the center
  of the universe. This was called geocentric.

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• Ptolemy thought that Earth is at the center of
  the system of planets, also.
• He thought that the planets move in little
  circles that move in bigger circles.
• This would help explain why the planets seem to
  move at different speeds, and even backwards.

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Copernicuss Idea Sun at the Center

• In the 1500s, the Polish astronomer Nicolaus
  Copernicus thought that the sun is at the center
  of the system of planets. His sun-centere system
  is called a heliocentric system. Helios is Greek
  for sun.

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Galileo Observations

• Galileo Galilei first scientist to use a
  telescope to look at objects in the sky. He
  supported the heliocentric model. He saw four
  moons revolving around Jupiter and this made him
  think that not everything revolves around Earth.

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Galileos Observations

• Galileo discovered that Venus goes through phases
  similar to those of Earths moon.

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Galileos Observations

• Today, people talk about the solar system
  rather than the Earth system.

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Brahe and Kepler

• Tycho Brahe, a Danish astronomer, observed the
  positions of the planets for 20 years.

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Brahe and Kepler

• Johannes Kelpler, a German mathematician,
  discovered that the orbit of each planet is an
  ellipse instead of circles.
• An ellipse is an elongated circle, or oval shape.
  

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Inertia and Gravity

• Sir Isaac Newton, an English scientist, studied
  why the planets stayed in the orbit.
• He concluded that two factors-inertia and
  gravity-combine to keep the planets in orbit.

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Inertia and Gravity

• Newton discovered that an object in motion will
  remain in motion unless some force acts to stop
  its motion. This is called inertia.
• Newton also hypothesized that the same force that
  pulls an apple to the ground also pulls the moon
  toward Earth. This is gravity.

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More to Discover

• Since Newton, our knowledge about the solar
  system has increased dramatically.
• Now astronomers know of three more planets -
  Uranus, Neptune, and Pluto.
• Astronomers have also identified comets and
  asteroids.
• We still use telescopes but we also use space
  probes to make observations of planets.

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20.3 Inner Planets
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Engage/Explore

• Name the planets in order.
• Pictures of the planets.

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Introduction

• Earth and the other three inner planets--Mercury,
  Venus, and Mars.
• The four inner planets are small and have rocky
  surfaces.
• These are called the terrestrial planets.

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Earth

• Earth has an atmosphere.
• Most of Earth, 70, is covered with water.
• Earth has three main layers.
• Earth has one moon called Luna.

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Mercury

• Closest to the sun.
• Not much larger than the Earths moon.
• Has no moons.
• The interior is made of iron and nickel.
• Mariner 10 photographed Mercury in 1974.

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Mercury

• It has a extremely thin atmosphere.
• It is so close to the sun that during the day,
  the side facing the sun reaches temperatures of
  430 degrees Celsius.
• Because Mercury has almost no atmosphere, at
  night all the heat escapes into spae and the
  temperature drops to -170 degrees Celsius.
• It has the greatest range of temperatures.

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Venus

• When you see a bright star during a sunset, it is
  probably Venus.
• It is similar to Earths size, sometimes called
  Earths twin.
• Takes about 7.5 Earth months to revolve around
  the sun.
• Venus has no moons.

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Venus

• It takes about 8 months to rotate on its axis.
• Its day is longer than its year.
• It rotates from east to west, which is opposite
  than most planets and moons. This is called
  retrograde rotation.

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Venus

• Its atmosphere is very thick. Venus never has
  sunny days.
• Venus pressure is 90 times greater than Earths
  atmosphere. So, you would be crushed. Also, the
  atmosphere is carbon dioxide and sulfuric acid.

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Venus

• Venuss surface gets hot because of the carbon
  dioxide, up to 460 degrees Celsius--hot enough to
  melt lead.
• This trapping of heat is called the greenhouse
  effect.

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Venus

• Venera 7 landed and sent back information on
  Venus. The Magellan probe also has collected
  lots of data on Venus.
• Venus has many rocky areas, volcanos, craters,
  and strange domes.

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Mars

• Called the red planet.
• Atmosphere is mostly carbon dioxide and has only
  1 the pressure of Earths atmosphere.
• You would have to wear an airtight suit and carry
  your own air to walk on Mars.
• The clouds are very thin.

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Mars

• In 1877, Giovanni Schiaparelli, an Italian
  astronomer, announced that he had seen long,
  straight lines on Mars. He called them channels.
  

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Mars

• Percival Lowell, an American astronomer,
  convinced many people that these lines were
  canals that had been built by intelligent
  Martians to carry water. Astronomers now know
  that Lowell was mistaken because there are no
  canals on Mars.

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Mars

• Ice remains on Mars at its north pole. At the
  south pole, it has an ice cap made mostly of
  frozen carbon dioxide.

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Mars

• Tilted axis so it has seasons. Mars has several
  wind storms and blows the dust around.
• Mars has giant volcanoes.
• Rocks look red because they are covered with a
  rusty dust.

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Mars

• Water flowed on Mars millions of years ago.
• Mars has two very small moons (Phobos, Deimos)

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The Outer Planets
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Structure of the Gas Giants

• The first four outer planets--Jupiter, Saturn,
  Uranus, and Neptune--are much larger than Earth,
  and do not have solid surfaces.
• They are called the gas giants.
• Jupiter is 11 times the size of Earth.
• Much stronger gravitational force
• Their atmospheres are similar to the suns
  atmosphere.
• Do not have a well-defined surface. You would be
  crushed due to the pressure.

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Structure of the Gas Giants

• Astronomers think that the outer planets have a
  solid core made of rock, ice, frozen carbon
  dioxide, and other compounds.

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Jupiter

• Most massive planet. It is 300 times as massive
  as Earth.
• Thick atmosphere made up of hydrogen and helium.
  
• Great Red Spot, a giant area of swirling clouds
  which appears to be an ongoing storm similar to a
  hurricane on Earth.

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Jupiter

• Galileo discovered four moons of Jupiter. They
  are Io, Europa, Ganymede, and Callisto.
  Astronomers has discovered a total of 17 moons
  around Jupiter.

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Jupiters moons

• Io is covered with volcanoes.
• From space, Io looks like a giant pizza.
• Europa has an icy crust that may have liquid
  water underneath.

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Jupiters moons

• Ganymede is the largest moon. Its surface is icy
  and partly covered with craters. It also shows
  giant grooves in the ice.
• Callisto has an icy surface and lots of craters.
  

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Saturn

• Second largest planet
• Thick atmosphere made of hydrogen and helium.
  Also contains clouds and storms.
• Saturn is less dense than water (1.0).

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Saturns Rings

• Saturns rings are made of chunks of ice and
  rock.
• Saturn has hundreds of rings.

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Saturns Moons

• Has 19 moons.
• Titan is Saturns largest moon. Titan has a very
  thick atmosphere.
• The other moons are Tethys, lapetus, Dione, and
  Rhea.

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Uranus

• Four times bigger than Earth.
• Twice as far from the Sun as Saturn.
• Very cold planet
• Looks blue due to traces of methane in the
  atmosphere.

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Uranus

• William Hershel, astronomer, discovered Uranus.

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Uranus

• Uranus axis is tilted at an angle of about 90
  degrees from the vertical.
• Uranus rotates top to bottom instead of from side
  to side.
• Uranus has 18 moons.

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Neptune

• Neptune contains visible clouds.
• Neptune has a Great Dark Spot. Probably a giant
  storm.
• Neptune has eight moons. Its largest moon is
  Triton.

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Pluto

• Solid surface
• Revolves around the sun once every 248 Earth
  years.
• Has one moon -Charon
• No longer called a planet.

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21.5 Comets, Asteroids, and Meteors

• Objective
• Identify the characteristics of comets and
  asteroids.
• Describe the formation of meteoroids.

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Comets

• Comet Hale Bopp was clearly visible in April
  1997.
• Comets are dirty snowballs about the size of an
  Earth mountain. Comets are chunks of ice and
  dust whose orbits are usually very long, narrow
  ellipses.

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Comets

• When at comet gets close to the sun, the energy
  in the sunlight turns the ice into gas, releasing
  dust.
• The outer layer of the gas and dust is called a
  coma.
• The inner layer is called the nucleus.
• Gas and dust form the comets tail.

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Comets

• Comets tail can be hundreds of millions of
  kilometers long. The material is stretched out
  very thinly so there isnt much mass in a comet
  tail.

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Comets

• In 1705, Edmond Halley, an English astronomer,
  realized that several comets seemed to have the
  same orbit and suggested that they were actually
  the same comet.
• He calculated that this comet appeared about
  every 76 years and that it would appear in 1758.
  The prediction came true, the comet was named
  Halleys comet.
• It last appeared in 1986.

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Asteroids

• Asteroids are small and too numerous to be
  considered fell-fledge planets.
• Most asteroids revolve around the sun between the
  orbits of Mars and Jupiter. This is known as the
  asteroid belt.
• Astronomers named four of them Ceres, Pallas,
  Juno, and Vesta between 1801-1807.

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Asteroids

• Asteroids could hit Earth.
• 65 million years ago, a large asteroid hit Earth
  making a crater 200 km in diameter near the
  Yucatan Peninsula of Mexico.
• Trillions of tons of dust went into the
  atmosphere blocking the sun for months. Started
  huge fires and destroyed the dinosaurs,
  scientists hypothesize.

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Meteors

• Have you ever seen shooting stars?
• What you saw was meteoroids.
• A meteoroid is a chunk or rock or dust in space.
  They usually come from comets or asteroids.

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Meteors

• When a meteoroid enters our atmosphere, it burns
  up and produces the streak of light--this is a
  meteor.
• Meteoroids that pass through the atmosphere and
  hit Earths surface are called meteorites.
  Meteorites cause craters on the moon and on
  Earth.
• This is Meteor Crater in Arizona.

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Meteors

• Meteorites fall all over Earth.
• Most look like stones.
• A few meteorites are entirely made of iron and
  nickel and are heavy.