The Cosmic Landscape
What is Out There?
God taking the measure
of the Universe
Have you comprehended
the expanse of the Earth?
Where is the way to the
dwelling of light,
And where is the place of
darkness…?
-The Book of Job
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The Earth, Our Home
• A sphere
– Fact known to ancient Greeks
– Radius 6400 km (4000 miles)
• Rotates — causes nights and days
• Has an atmosphere — held by Earth’s gravity
• Has a magnetic field — deflects compass needles
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The Earth
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The Moon
• Orbits Earth — held in orbit by Earth’s gravity
• Distance = 384,000 km (240,000 miles)
• A sphere
– Radius
1/4 of Earth’s radius
• Mass much smaller than Earth’s
– Consequently, has much weaker gravity
• No atmosphere because of the weak gravity
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The Moon
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The Inner Planets
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Mercury — barren, Sun-scorched
Venus — dense clouds of sulfuric acid
Earth — water
Mars — deserts and huge canyons
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The Outer Planets
• Jupiter
– immense mass, lightning storms
– powerful, long-lasting storms
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Saturn — ring system (trillions of ice fragments)
Uranus — tilted axis
Neptune — methane clouds
Pluto — Is it a planet?
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1. Mercury
3. Earth
5. Jupiter
7. Uranus
6. Saturn
2. Venus
8. Neptune
4. Mars
9. Pluto
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Portraits of the planets
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The Solar System
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Flattened shape
Held together by gravity
Nine planets
Asteroids (Minor Planets)
Comets
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The Sun
• Gaseous, roughly 3 parts Hydrogen & 1 part Helium
• Gravity
– Holds itself together by its own gravity
– Holds Earth and other planets in orbits
• Magnetic field — sunspots
• Hot — heated by nuclear reactions
– Surface Temp
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6000 K;
Core Temp
15 million K
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Sun viewed through a filter
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Scales of Distance
• Earth radius for planetary sizes
– Venus
– Jupiter
0.95
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• Astronomical Unit (AU)
– 1 AU
– 1 AU
150 million km
1.5×1011 m
• Light Year
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93 million miles
9.5×1015 m (6 trillion miles)
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Artist’s view of the Solar System
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The Milky Way Galaxy
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Our Home Galaxy
100 billion stars
80,000 ly across
Spiral arm structure
Sun orbits once every 240 million years
Possible black hole at the core
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Artist’s view of the Milky Way
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Interstellar clouds in the Milky Way
© Anglo -Australian Observatory. Photograph by David Malin.
(http://WWW.AAO.GOV.AU/images.html)
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© Anglo -Australian Telescope Board (http://WWW.AAO.GOV.AU/images.html)
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Galaxy Clusters and the Universe
• Milky Way belongs to the Local Group
– about 30 galaxies
• Local Supercluster
• The Great Attractor
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Milky Way and local Supercluster
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How the Earth fits
into the Universe
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An atom
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