The Sizes and Numbers of Objects in the Universe

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The Sizes and Numbers of Objects in the Universe
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Solar System Inventory 1 Star
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Solar System Inventory9 Planets
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The Terrestrial Planets
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The Jovian Planets
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Solar System Inventory91 moons
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Solar System InventoryCountless numbers of
Asteroids, Comets, Meteors, Dust
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Terrestrial Characteristics

• Metallic core
• Oxygen dominated (silicates)

Material (by mass) Iron 35 Oxygen 30 Silicon
15 Magnesium 13 Nickel 2.4 Sulfur 1.9
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Terrestrial Characteristics

• Thin (or nonexistent) atmospheres
• Few (or no) natural satellites
• Closely spaced orbits

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Jovian Characteristics

• Solid metallic-rocky cores
• Hydrogen dominated

Material (by mass) Hydrogen 74 Helium 24 Wate
r 0.6 Methane 0.4 Ammonia 0.1 Rock Metals 0.3
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Jovian Characteristics

• Thick gaseous atmospheres
• Many natural satellites
• Widely spaced orbits

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Pluto-Like?
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Cosmic Distances

• Astronomical units of distance
• Astronomical Unit The distance between the Sun
  and the Earth
• 93 million miles
• Light year The distance light travels in a year
• Speed of light 186,282 miles/sec
• Light year 5.9 trillion miles

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The Sizes of Stars in our Universe
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The Distribution of Stars in the Universe
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How many stars are in the Milky Way?
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How many stars are in the Milky Way?

• Orbital periodsun 240 million years
• Orbital distancesun 28,000 light years
• Mgal ? 100 billion Msun

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Does this represent the actual number of stars in
our galaxy?

• Our Sun is an average star in mass and
  luminosity.
• The galaxy has many more low mass stars compared
  to high mass stars
• Adjusted estimate of stars in Milky Way 300
  400 billion stars

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How are the galaxies distributed in the Universe?
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