Announcements

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Announcements

• Bachelor of Fine Arts with Emphasis in Art
  Education Program (BFAAE)
• Deadline for application is March 1
• Dave Snyder, math tutor (email dsnyde)
• Wed 1100 200 MI B1-05
• Thurs 200-500 MI B1-05

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Summary of Last Class Science

• Science is a process
• Observations
• Theories to unify/explain observations
• Tests of theories against observations...
• Etc
• Testing theories is the only way to weed out
  falsehoods!
• All theories that survive so far are current best
  explanations, backed by evidence
• But any theory could be disproven with the next
  observation

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Summary of Last Class Life

• Life is complex compared to not-life
• Reproduces
• Adapts
• Stays alive
• BEHAVES
• Nothing is ruled out, but life we can interact
  with likely requires
• Carbon (but carbon's everywhere!)
• Liquid solvent like water (Narrow temperature
  range!)

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Feedback

• Most unclear item from last week's readings?

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Feedback

• How much time was spent on readings?
• How much time was spent on homework?

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Projects/Presentations

• Only a few interested in presentations good
• If interested in Mar 12 presentation, sign up now
  (can change mind later)
• Presentation, Report, Art project, same goal
• Demonstrate an understanding of some significant
  amount of course-related material.
• Topics need to be checked with me
• (jdursi _at_ artic.edu)

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Possible Topics

• NASA Terrestrial Planet Finder
• Sattelite intended to go up in next decade to
  search for Earth-like planets
• The Formation of Stars
• The Formation of Planets
• History of thought on extraterrestrial life
• Extremophiles
• Earth organisms that live in extreme conditions
• Life on gas giants how?
• ....

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What we're going to cover today

• What's in the Universe and where it is The
  Distance Ladder
• Objects
• The distance scale from the moon to distant
  galaxies
• The Drake Equation
• Estimating the number of civilizations in the
  Galaxy

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The Universe and How Big it isThe Contents

• At end of this lecture/reading, should be able
  to
• Explain what major sorts of objects are seen (by
  eye!) in night sky, and how to distinguish them
• Stars
• Planets
• Galaxies
• Clusters
• Nebulae

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The Night Sky
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Objects

• Point objects
• Stars
• Big point' objects
• Overexposed stars
• Extended objects
• Some fuzzy, some not
• ??

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Other Objects

• Planets
• Like stars fairly bright, move around on paths
• Transient events
• Comets
• Meteors
• Novae' (rare)

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Nature of fuzzy objects unclear for centuries

• 1610 Orion nebula discovered with new
  telescope' by de Peiresc
• 1656 Huygens examined more carefully
• 1700s astronomers looking for comets these
  nebulous' objects were irritating distractions
• Messier catlogued 103 so that comet hunters
  wouldn't confuse them for comets.

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Nature of fuzzy objects unclear for centuries

• Herschels composed more detailed catalogue (NGC)
  until 1802
• 2500 objects
• Suplemented by Index Catalogues (IC) up to 1905
• 5,386 additional objects
• Astrophotography couldn't take decent pictures
  until 1883
• Long exposures much better images

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Large numbers of types

• Some were clearly nearby gas clouds lit up by
  central star
• Others were fairly clearly more distant clusters
  of stars
• Spiral nebulae remained a mystery.

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What are they?

• 1920 Shapley-Curtis Debate
• Shapley
• Spiral Nebulae' were just near by gas clouds
  the universe consisted of only one galaxy
• Curtis
• Spiral Nebulae are very very far away
• To be seen at this distance, must be huge --- as
  big as our own galaxy
• We live in just one of many galaxies!!

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Importance of Distance

• Nature and scale of the universe hinged on
  argument of how distant things are
• Determines their size
• Astronomers can't see' distances!

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The Universe and How Big it isThe Distance
Ladder

• At end of this lecture/reading, should be able
  to
• Describe relative scales of
• stars/planets
• Stellar systems
• Interstellar distances
• Galactic Distances
• Intergalactic Distances
• And explain how those distances are measured

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The Distance Ladder

• Need to measure nearby distances
• Use those to measure distance to more remote
  objects
• Build our way up from solar system to entire
  observable universe
• Excellent website
• http//heasarc.gsfc.nasa.gov/docs/cosmic/

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Begin with most nearby object
http//www.rathergood.com/moon_song
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Lessons from Educational Video

• Some confusion about distance to moon
• Difficulty comparing it with other distances
• Zeppelin
• Dirigible
• Light bulbs
• Puffins

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Relative Size of Earth, Moon

• Aristarchus of Samos (310-230 BC)
• Lunar Eclipse Moon in Earths Shadow
• 1.25 hour

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Relative Size of Earth, Moon

• Takes moon about 28 days to circle the earth
• 360 degrees
• Travels a bit over a degree an hour
• Moon size is 0.5 degrees
• Travels a bit over 2 of its own sizes an hour
• Travels about 3 of its sizes during an eclipse
• Earth's shadow size 3 moon sizes
• Earth 3x size of moon

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Another eclipse way to measure relative size
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Another eclipse way to measure relative size
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Can also determine Distance to moon relative to
Distance to sun

• Very tricky to measure!
• Moon has to be exactly at full moon angle to sun
  is very nearly 90 degrees (89.85)

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Radius of Earth

• Eratosthenes (276-196 BC)
• Difference in angles cast by shadows from the
  distant sun
• Found an earth radius of 40,000 miles within a
  few percent of accepted value today.

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Suddenly

• Know actual size of moon
• Since know its size and how big it seems, know
  distance to moon
• Know distance to sun
• Today, can verify/improve these distances
• Radar
• Space probes
• Orbit modeling
• Get us accurate measurements of entire solar
  system

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New length unit Astronomical Unit (AU)

• Earth-Sun distance so handy for measuring solar
  system distances that new unit created
• 1 AU mean distance between Earth and Sun
• 1 AU 92,955,807 miles

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Distances to stars

• Activity building a constellation

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Paralax

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  01234

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Paralaxes can be observed in stars
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Paralaxes can be observed in stars
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What Is Science Not Good At?
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(No Transcript)
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The displacement is measured as an angle on the
sky

• 0.5 degree about your thumb at arms length
• 1 arc minute 1/60th of a degree
• 1 arc second 1/60th of an arc minute
• A distance at which the parallax (from Jan to
  June) is 1 arc second is a parsec (PARallax
  SECond)
• Can find it from 1 AU with some trig
• 1 pc 206265 AU

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Concept Test

• Would a parmin'' (PARallax MINute) be a LARGER
  unit of distance, or a SMALLER unit of distance
  than a parsec?

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Concept Test

• Would a parmin'' (PARallax MINute) be a LARGER
  unit of distance, or a SMALLER unit of distance
  than a parsec?
• Smaller.
• An arc minute is a BIGGER displacement
• CLOSER stars would have bigger displacements
  something that had a paralax of an arc minute
  would be closer.
• (60 times closer!)

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Distances to nearby clusters of stars

• Many techniques
• Simplest is Spectroscopic parallax (not really a
  parallax measure)
• Cluster will contain lots of stars like ones
  nearby
• Know their distance, brightness well
• Can calibrate distance to cluster by inferring
  distance to individual stars

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Distances to nearby clusters of stars

• Other techniques
• Globular clusters tend to have similar sizes can
  infer distance from apparent size
• Use motions of stars within cluster as yardstick

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Distances to distant clusters of stars

• Clusters also contain stars such as RR Lyrae or
  Cephieds
• Variable stars
• Pulse over days
• Pulsation period tells you their brightness
• Bright enough to be seen in quite distant clusters

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Distances to nearby galaxies

• Cepheids can even be seen in our galactic
  neighbors, so can measure distances to galaxies
  directly!

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Stringing together a Universe

• Activity putting relative distances in
  perspective

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Stringing together a Universe

• 1 tic 1 AU (earth-sun distance)

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Stringing together a Universe

• 10 tic 1 pc (typical inter-stellar distance)
• (1 tic 1/10 pc 20,600 AU)

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Stringing together a Universe

• 4 tic 1 kpc (typical inter-stellar distance)
• (1 tic 1/4 kpc 250 pc 51 million AU)

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The Drake Equation

• Drake Equation will structure the rest of our
  class
• Astronomy
• Number of stars in galaxy
• Number of suitable stars
• Number of stars that form planets
• Geophysics
• Number of planets suitable for life
• Biology
• Where and low life forms on those planets