Announcements

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Announcements

• Turn in Homework 14 (5 questions)
• Today is the deadline for the Monty Python
  challenge!
• Observatory session tonight, weather permitting
• Review session on Friday
• Final Exam next Monday or Tuesday 2 hours, 100
  points, comprehensive, with an emphasis on
  galaxies and cosmology

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Book Recommendation
365 Starry Nights, by Chet Raymo My favorite
guide to the constellations hand-drawn, grouped
by season, with a miniature lesson on mythology
or astronomy for each night of the year.
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Course Outline

• Naked-eye astronomy
• Crash course in physics
• Our solar system
• The stars
• Structure and history of the  universe

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The Observable Universe
Galaxy
Dark era
Quasar
Background radiation (3000-degree ionized gas)
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We can use redshifts to map the universe
You are here!
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Virgo Cluster
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M83
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Inside the Milky Way
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The Outer Solar System
Neptune
On this scale 1 A.U. 7 pixels Orbital
radii Jupiter 5.2 A.U. Saturn 9.5
A.U. Uranus 19 A.U. Neptune 30 A.U.
Uranus
Saturn
Jupiter
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The Inner Solar System
Mars
Earth
On this scale 1 A.U. 120 pixels Diam. of Sun
1 pixel Diam. of moons orbit 1/2 pixel Diam.
of earth 1/100 pixel
Venus
Mercury
Sun
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Earth and Moon to scale
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Home!
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Life in the Universe

• 6 December 2006

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Today

• History of life on earth
• Search for life in the solar system
• Life in other solar systems? How to tell?
• Why arent they here (or are they)?

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Earth Life
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History of Life on Earth

• Bacteria (simple cells) 3 billion years ago
• Complex cells about 1 billion years ago
• Multicellular life 700 million years ago
• Humans
• Agriculture 10,000 years ago
• Radio communication 100 years ago
• Space travel 45 years ago

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The planets, to scale
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The Terrestrial Worlds
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Life on Mars?

• Past robotic visits found no clear sign of life
• Allen Hills meteorite inconclusive
• Robotic exploration has discovered pretty good
  evidence for past surface water

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Europa Water beneath ice
Water is probably kept warm by tidal friction.
Could this be a place to look for life?
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Titan (Saturns largest moon)
Opaque atmosphere of nitrogen, methane, smog.
Surface (cold!) could have liquid methane, other
hydrocarbons. Huygens probe landed in Jan. 2005.
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What about other solar systems?

• Planets seem to be common around other stars
• Hot, massive stars probably dont live long
  enough for life (as we know it) to develop
• Cool, low-mass stars are unlikely to have
  earth-like planets with liquid water
• Best bet sun-like stars, which are still fairly
  common (perhaps 1010 in our galaxy).
• But we cant go there (in the foreseeable
  future), so how can we learn if theres life?

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3 ways to look for life in other solar systems

• Look for clues in spectra. For example, an
  atmosphere with abundant oxygen would probably
  indicate the presence of life, and may be
  detectable with future instruments
• Look/listen for artificial signals from
  extraterrestrial civilizations
• Speculate

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Search for Extraterrestrial Intelligence
Jodi Foster in Contact (heard a message from an
alien civilization and got to go for a visit!)
Dr. Jill Tarter, SETI Institute (hasnt heard
any messages yet!)
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Speculations are easy

• Simple life may be relatively common in the
  universe
• Multicellular life is probably much less common,
  since it may require rather rare conditions
  (stable environment for billions of years)
• Intelligent life is probably still less common
• Technological civilizations comparable to ours
  would be rarer still, but may develop far
  superior technologies in a cosmic nanosecond
• What are the chances that we would discover such
  a civilization, or that they would discover us?

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Or have they?
(And if you believe everything you see on Fox)
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Seriously, why arent they here?

• Maybe they arent there!
• Or maybe interstellar travel is just too
  difficult
• Or maybe they just arent interested.

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The bottom line?
We really have no idea whether life exists
elsewhere, let alone intelligent life or advanced
civilizations. Everyone seems to have an
opinion, but by and large, these opinions are
based upon personal wishes, not facts. Part of
being scientific is setting personal wishes
aside and admitting when you just dont know.