chapter01 - Chapter 1 Our Place in the Universe 1.1 A...

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Chapter 1 Our Place in the Universe
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1.1 A Modern View of the Universe What is our place in the universe? How did we come to be? How can we know what the universe was like in the past? Can we see the entire universe? Our goals for learning:
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What is our place in the universe?
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A large, glowing ball of gas that generates heat and light through nuclear fusion Star
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Planet A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition. Mars Neptune
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Moon (or satellite) An object that orbits a planet. Ganymede (orbits Jupiter)
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Asteroid A relatively small and rocky object that orbits a star. Ida
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Comet A relatively small and icy object that orbits a star.
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Solar (Star) System A star and all the material that orbits it, including its planets and moons
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Nebula An interstellar cloud of gas and/or dust
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Galaxy A great island of stars in space, all held together by gravity and orbiting a common center M31, The Great Galaxy in Andromeda
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Universe The sum total of all matter and energy; that is, everything within and between all galaxies
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How did we come to be?
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How can we know what the universe was like in the past? Light travels at a finite speed (300,000 km/s). Thus, we see objects as they were in the past: The farther away we look in distance, the further back we look in time. Destination Light travel time Moon 1 second Sun 8 minutes Sirius 8 years Andromeda Galaxy 2.5 million years
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Example: We see the Orion Nebula as it looked 1,500 years ago. M31, The Great Galaxy in Andromeda
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Example: This photo shows the Andromeda Galaxy as it looked about 2 1/2 million years ago. Question: When will be able to see what it looks like now? M31, The Great Galaxy in Andromeda
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Light-year The distance light can travel in one year. About 10 trillion km (6 trillion miles).
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At great distances, we see objects as they were when the universe was much younger.
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How far is a light-year? 1light-year = (speed of light) × (1 year) =300,000 km s × 365 days 1 yr × 24 hr 1 day × 60 m in 1 hr × 60 s 1 m in
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How far is a light-year? 1light-year = (speed of light) × (1 year) = 300,000 km s × 365 days 1 yr × 24 hr 1 day × 60 min 1 hr × 60 s 1 min =9,460,000,000,000 km
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Can we see the entire universe?
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Because no galaxies exist at such a great distance.
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chapter01 - Chapter 1 Our Place in the Universe 1.1 A...

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