Astronomy 100 Tuesday, Thursday 2:30 3:45 pm Tom Burbine tburbinemtholyoke'edu www'xanga'comastronom

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Astronomy 100Tuesday, Thursday 230 - 345
pmTom Burbinetburbine_at_mtholyoke.eduwww.xanga.
com/astronomy100
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PRS and HW grades

• 100 PRS and 100 HW scores will bring up a
  persons total exam score by 4-6 points

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• A 92.50 - 100
• A- 89.50 92.49
• B 87.50 89.49
• B 82.50 87.49
• B- 79.50 82.49
• C 77.50 79.49
• C 72.50 77.49
• C- 69.50 72.49
• D 67.50 69.49
• D 62.50 67.49
• D- 59.50 62.49
• F below 59.49

If the class average is 80 or higher, the grade
distribution will be something like this
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Schedule

• May 3 (Does Life Exist Elsewhere in the Universe)
• May 5 (Review)
• May 10 (Exam 4)
• May 12 (Exam 5) (optional)
• May 20 (Final) (optional)

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Exam 4

• Know the class notes
• Know all the definitions on the website
• Know the Summary of Key Concepts at the end of
  every chapter

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Exam 5 and Final

• Know the class notes
• Know how to do every question on the 1st 4 exams
• Know the Summary of Key Concepts at the end of
  every chapter

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Homework Assignment(Due Today)

• Make up a test question for next test
• Multiple Choice
• A-E possible answers
• 1 point for handing it in
• 1 point for me using it on test
• The question needs to be on material that will be
  on the 4th exam

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Homework Assignment(Due Thursday)

• I have placed 40 terms on the website
• You get 0.1 of a HW point for each of these you
  define and hand in to me
• Definitions need to be hand-written or hand-typed
• A lot of these definitions will be on next test

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• Drake Equation
• Dark Energy
• Tully-Fisher Relation
• ALH84001
• Cepheid Variable
• White Dwarf
• Jocelyn Bell
• Viking Mission
• Hubbles Law
• SETI
• Big Bang
• COBE
• Standard Candle
• Quasar
• Planck Time
• Inflation in the Early Universe
• Olbers Paradox
• Cosmic Microwave Background
• Isotope

• Percival Lowell
• Redshift
• Dark Matter
• MACHO
• Critical Density
• Radio Galaxy
• Main Sequence Fitting
• Cosmological Horizon
• White Dwarf Supernova
• Interstellar Medium
• Supercluster
• WIMP
• Pulsar
• Habitable Zone
• Maunder Minimum
• Convection Zone
• Radiation Zone
• Hubbles Constant
• Starburst Galaxy

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Astronomy Help Desk

• There is an Astronomy Help Desk in Hasbrouck 205.
  
• It is open Monday through Thursday from 7-9 pm.

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Dark Energy

• The universe appears to be accelerating
  (expanding faster)
• Dark Energy is proposed as the cause
• Pushing galaxies apart

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Basic Definition of Life

• Growth
• Metabolism
• Motion
• Reproduction
• Stimulus response

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Percival Lowell (1855-1916)

• Lowell produced intricate drawings of the Red
  Planet
• Finding hundreds of straight lines (termed
  "canals")

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He thought

• Lowell concluded that the bright areas were
  deserts and the dark were patches of vegetation
• Lowell thought the canals were constructed by
  intelligent beings who once flourished on Mars.

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For years

• People thought life could exist on Mars and
  Venus, the closest planets to Earth

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However,

• Venus is extremely hot (700-800 K)
• Atmospheric pressure is 90 times that of Earth

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Mars

• The average recorded temperature on Mars is
  -63 C with a maximum temperature of 20 C and a
  minimum of -140 C
• Atmospheric pressure is 1/100 of Earths

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In the past

• Mars appeared to be warmer and wetter

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ALH84001

• Allan Hills 84001
• Martian meteorite found in Antarctica
• Thought to have evidence for life

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Evidence

• organic molecules
• Magnetite that looks like it formed from biologic
  activity
• nanofossil-like structures

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Key to Life

• All life on Earth depends on water
• So if you find water, you may find life

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Habitable Zone

• The region around a star in which planets could
  potentially have surface temperatures which
  liquid water could exist

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Viking Missions

• Missions to Mars in 1976 to look for Life
• Two Missions to Mars to look for Life

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Experiments

• Three of the four experiments to look for life
  produced positive results
• But results could all be explained through
  non-biologic chemistry

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Pyrolytic-Release (PR) experiment

• A mixture of radioactive CO2 and CO was
  introduced into a vessel containing a soil sample
• Sample was irradiated with light
• Then gases flushed out
• Heated
• Detector measured radioactive carbon compound
  given off from heating
• Probably due to non-biologic reactions in soils
  and not life

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SETI

• Search for Extraterrestrial Intelligence
• Search for signals from other civilizations

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Drake Equation

• Calculates how many civilizations are out there
  in our galaxy now

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Version of Formula

• Number of civilizations that exist today
• the number of habitable planets in the galaxy
  times
• the fraction of planets that have life in the
  galaxy times
• the fraction of the life-bearing planets in
  the galaxy upon which a civilization capable of
  interstellar communication has at some time
  arisen times
• the fraction of all civilizations that have
  existed in the galaxy that exist now

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Number of habitable planets

• 100 billion?

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Fraction of Planets that have life in the Galaxy

• ?

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Fraction of the Life-Bearing Planets in the
Galaxy upon which a Civilization capable of
interstellar communication has at some time
arisen

• ?

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Intelligent Life

• Intelligent life that we can detect is usually
  defined as life that can build a radio telescope

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Radio

• Transmitting information over radio waves is very
  cheap
• uses equipment that is easy to build
• has the information-carrying capacity necessary
  for the task
• The information also travels at the speed of
  light.

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Fraction of all civilizations that have existed
in the galaxy that exist now

• ?

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Fermis Paradox

• Where are they?

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Fermis Paradox

• Why have we not observed alien civilizations even
  though simple arguments would suggest that some
  of these civilizations ought to have spread
  throughout the galaxy by now?

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Reason for question

• Straightforward calculations show that a
  technological race capable of interstellar travel
  at (a modest) one tenth the speed of light ought
  to be able to colonize the entire Galaxy within a
  period of one to 10 million years.

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Explanation

• Interested in us but do not want us (yet) to be
  aware of their presence (sentinel hypothesis or
  zoo hypothesis)

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Explanation

• Not interested in us because they are by nature
  xenophobic or not curious

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Explanation

• Not interested in us because they are so much
  further ahead of us

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Explanation

• Prone to annihilation before they achieve a
  significant level of interstellar colonization,
  because     (a) they self-destruct     (b) are
  destroyed by external effects, such as
          (i) the collision of an asteroid or
  comet with their home world         (ii) a
  galaxy-wide sterilization phenomenon (e.g. a
  gamma-ray burster       (iii) cultural or
  technological stagnation

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Explanation

• Capable of only interplanetary or limited
  interstellar travel because of fundamental
  physical, biological, or economic restraints

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Questions