1. Our Solar System
Who is Stan Hatfield and Ken Pinzke

2. Early Astronomy Ancient Greeks  Geocentric Model  Heliocentric Model
• In the ancient Greeks’ geocentric model, the moon, sun, and the known planets—Mercury, Venus, Mars, and Jupiter—orbit Earth.
 Heliocentric Model
• In the heliocentric model, Earth and the other planets orbit the sun.

3. Geocentric and Heliocentric Models
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4. Early Astronomy Ancient Greeks  Ptolemaic System
• Ptolemy created a model of the universe that accounted for the movement of the planets.
• Retrograde motion is the apparent westward motion of the planets with respect to the stars.

5. Retrograde Motion
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6. Early Astronomy The Birth of Modern Astronomy  Johannes Kepler
• Kepler discovered three laws of planetary motion:
1. Orbits of the planets are elliptical.
2. Planets revolve around the sun at varying speed.
3. There is a proportional relationship between a planet’s orbital period and its distance to the sun.

7. Early Astronomy The Birth of Modern Astronomy  Johannes Kepler
• An ellipse is an oval-shaped path.
• An astronomical unit (AU) is the average distance between Earth and the sun; it is about 150 million kilometers.

8. Early Astronomy The Birth of Modern Astronomy  Galileo Galilei
• Galileo’s most important contributions were his descriptions of the behavior of moving objects.
• He developed his own telescope and made important discoveries:
1. Four satellites, or moons, orbit Jupiter.
2. Planets are circular disks, not just points of light.
3. Venus has phases just like the moon.
4. The moon’s surface is not smooth.
5. The sun has sunspots, or dark regions.

9. The Earth–Moon–Sun System
Motions of Earth
The Earth–Moon–Sun System
 **Rotation
• Rotation: turning/spinning, of a body on its axis.
• Two measurements for rotation:
1. **Mean solar day is the time interval from one noon to the next, about 24 hours.
2. **Sidereal day is the time it takes for Earth to make one complete rotation (360º) with respect to a star other than the sun—23 hours, 56 minutes, 4 seconds.

10. Sidereal Day
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11. The Earth–Moon–Sun System
Motions of Earth
The Earth–Moon–Sun System
 Revolution
• **Revolution: motion of a body, such as a planet or moon, along a path around some point in space.
• Perihelion: in January when Earth is closest to the sun.
• Aphelion: in July when Earth is farthest from the sun.

12. The Earth–Moon–Sun System
Motions of Earth
The Earth–Moon–Sun System
 Earth’s Axis and Seasons
• The plane of the ecliptic is an imaginary plane that connects Earth’s orbit with the celestial sphere.
• *Because of the inclination of Earth’s axis to the plane of the ecliptic, Earth has its yearly cycle of seasons.

13. The Solar System The Planets: An Overview
 terrestrial planets: planets that are small and rocky—Mercury, Venus, Earth, and Mars.
 Jovian planets: are the huge gas giants—Jupiter, Saturn, Uranus, and Neptune.
 Pluto does not fit into either the Jovian or the terrestrial category.

14. Orbits of the Planets
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15. The Solar System The Planets: An Overview
 Size is the most obvious difference between the terrestrial and Jovian planets.
 Density, chemical makeup, and rate of rotation are other ways in which the two groups of planets differ.

16. Planetary Data
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17. The Solar System The Planets: An Overview
 The Interiors of the Planets
• The substances that make up the planets are divided into three groups: gases, rocks, and ices.
 The Atmosphere of the Planets
• The Jovian planets have very thick atmospheres of hydrogen, helium, methane, and ammonia.
• By contrast, the terrestrial planets, including Earth, have meager atmospheres at best.

18. Scale of the Planets
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19. The Solar System Formation of the Solar System  Nebular Theory
• nebula: cloud of gas and/or dust in space.
sun and planets formed from a rotating disk of dust and gases.

20. The Solar System Formation of the Solar System  Planetesimals
• Planetesimals: small, irregularly shaped bodies formed by colliding matter.

21. Formation of the Universe
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22. Planetary Composition, Distance from the Sun, and Melting Point
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23. The Terrestrial Planets
Mercury: The Innermost Planet
The Terrestrial Planets
 Mercury: innermost and 2nd smallest planet; it is hardly larger than Earth’s moon.
 Surface Features
• Mercury has cratered highlands, much like the moon, and vast smooth terrains that resemble maria.
 Surface Temperatures
• Mercury has the greatest temperature extremes of any planet.

24. Mercury’s Surface
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25. The Terrestrial Planets
Venus: The Veiled Planet
The Terrestrial Planets
 Surface Temperatures
• The surface temperature of Venus reaches 475oC, and its atmosphere is 97% carbon dioxide.

26. The Terrestrial Planets
Venus: The Veiled Planet
The Terrestrial Planets
 Venus - similar to Earth in size, density, mass, and location in the solar system. Thus, it has been referred to as “Earth’s twin.”
 Surface Features
• Venus is covered in thick clouds that visible light cannot penetrate.
• About 80 percent of Venus’s surface consists of plains covered by volcanic flow.

27. Venus
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28. The Terrestrial Planets
Mars: The Red Planet
The Terrestrial Planets
 The Martian Atmosphere
• The Martian atmosphere has only 1 percent of the density of Earth’s.
• Although the atmosphere of Mars is very thin, extensive dust storms occur and may cause the color changes observed from Earth.
 Surface Features
• Most Martian surface features are old by Earth standards. The highly cratered southern hemisphere is probably 3.5 billion to 4.5 billion years old.

29. Mars
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30. The Terrestrial Planets
Mars: The Red Planet
The Terrestrial Planets
 Water on Mars
• Some areas of Mars exhibit drainage patterns similar to those created by streams on Earth.
• Images from the Mars Global Surveyor indicate that groundwater has recently migrated to the surface.

31. Water on Mars
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32. The Outer Planets

33. The Outer Planets Jupiter: Giant Among Planets
 Jupiter: a mass that is 2 1/2 times greater than the mass of all the other planets and moons combined.
 Structure of Jupiter
• Jupiter’s hydrogen-helium atmosphere also contains small amounts of methane, ammonia, water, and sulfur compounds.

34. Jupiter and the Great Red Spot
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35. The Outer Planets Jupiter: Giant Among Planets  Jupiter’s Moons
• Jupiter’s satellite system, including the 69 moons discovered so far, resembles a miniature solar system.
 Jupiter’s Rings
• Jupiter’s ring system was one of the most unexpected discoveries made by Voyager 1.

36. Jupiter’s Largest Moons
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37. The Outer Planets Saturn: The Elegant Planet
 The most prominent feature of Saturn is its system of rings.
 Features of Saturn
• Saturn’s atmosphere is very active, with winds roaring at up to 1500 kilometers per hour.
• Large cyclonic “storms” similar to Jupiter’s Great Red Spot, although smaller, occur in Saturn’s atmosphere.

38. Cassini Approaching Saturn
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39. The Outer Planets Saturn: The Elegant Planet  Saturn’s Rings
• Until the discovery that Jupiter, Uranus, and Neptune have ring systems, this phenomenon was thought to be unique to Saturn.
• Most rings fall into one of two categories based on particle density.
 Saturn’s Moons
• Saturn’s satellite system consists of 60+ moons.
• Titan is the largest moon, and it is bigger than Mercury.

40. Saturn’s Rings
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41. The Outer Planets Uranus: The Sideways Planet
 Instead of being generally perpendicular to the plane of its orbit like the other planets, Uranus’s axis of rotation lies nearly parallel with the plane of its orbit.

42. Uranus
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43. The Outer Planets Neptune: The Windy Planet
 Winds exceeding 1000 kilometers per hour encircle Neptune, making it one of the windiest places in the solar system.

44. Neptune
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45. The Outer Planets Pluto: Planet X
 Pluto’s orbit is highly eccentric, causing it to occasionally travel inside the orbit of Neptune, where it resided from 1979 through February 1999.

46. Word Bank Telescope Solar nebula Perihelion Terrestrial planets
Planet Orbital period
Aphelion Solstice
Kuiper belt Equinox
Rotation Galaxy
Gas giant Revolution
Solar system Inertia

47. Minor Members of the Solar System
Asteroids: Microplanets
Minor Members of the Solar System
 asteroid: small, rocky body [dia. = less than a km to 100’s of km]
 Most asteroids lie between Mars and Jupiter. They have orbital periods of three to six years.

48. Irregular Orbits of Asteroids
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49. Minor Members of the Solar System
Comets
Minor Members of the Solar System
 Comets: small bodies made of rocky and metallic pieces held together by frozen gases. Comets generally revolve about the sun in elongated orbits.

50. Minor Members of the Solar System
Comets
Minor Members of the Solar System
 Coma
• coma: fuzzy, gaseous component of a comet’s head.
• A small glowing nucleus with a diameter of only a few kilometers can sometimes be detected within a coma. As comets approach the sun, some, but not all, develop a tail that extends for millions of kilometers.

51. Comet’s Tail Points Away from the Sun
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52. Minor Members of the Solar System
Comets
Minor Members of the Solar System
 Kuiper Belt
• Like the asteroids in the inner solar system, most Kuiper belt comets move in nearly circular orbits that lie roughly in the same plane as the planets.

53. Minor Members of the Solar System
Comets
Minor Members of the Solar System
 Halley’s Comet
• The most famous short-period comet is Halley’s comet. Its orbital period is 76 years.

54. Minor Members of the Solar System
Meteoroids
Minor Members of the Solar System
 meteoroid: small, solid particle that travels through space.
 meteor: when a meteoroid enters Earth’s atmosphere and burns up, popularly called a shooting star.
 meteorite: is any portion of a meteoroid that reaches Earth’s surface.

55. Minor Members of the Solar System
Meteoroids
Minor Members of the Solar System
 Most meteoroids originate from any one of the following three sources: (1) interplanetary debris that was not gravitationally swept up by the planets during the formation of the solar system, (2) material from the asteroid belt, or (3) the solid remains of comets that once traveled near Earth’s orbit.

56. Major Meteor Showers
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