Starry%20Monday%20at%20Otterbein

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Starry Monday at Otterbein
Welcome to

• Astronomy Lecture Series
• -every first Monday of the month-
• April 3, 2006
• Dr. Uwe Trittmann

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Todays Topics

• Introduction to Cosmology
• The Night Sky in April

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On the Web

• To learn more about astronomy and physics at
  Otterbein, please visit
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Observatory)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

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Cosmology

• The part of astronomy (and astrophysics) that
  deals with the greatest structures in the
  universe and the evolution of the universe
  itself!
• The start of the universe, a primordial
  fireball
• ? the early universe was very hot and dense
• ? intimate connection between cosmology and
  nuclear/particle physics
• ? To understand the very big we have to
  understand the very small

Big Bang
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Questions, Questions, Questions

• Scientists want to know, so they ask questions
• What is in the universe?
• How do these things interact?
• How does the universe change in time?
• Is there a beginning?
• Is there an end?

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Whats in the Universe?

• Answers come from observations
• ? Lets observe

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The Earth
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Planets
Mercury
Venus
Mars
Jupiter
Saturn
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The Sun (a typical star)
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Stars
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Galaxies
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Clusters of Galaxies
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Whats in the Universe?
Big ..small
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Whats in the Universe?

• A lot of stuff !!!
• Scientific term Mass

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Observation II It is dark at night!

• Big deal!
• Indeed it has cosmological consequences!
• Lets find out why!

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Night sky No sun just stars
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Look closer and find more dimmer stars
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If the Universe is infinite
Theres more and more
dimmer and dimmer stars
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Until finally
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the view fills up completely
and its as bright as the day!
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So, why is the night sky dark?(Olbers Paradox)

• Conclusion either
• Universe is not infinite or
• Universe changes in time

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Observation III Everything is moving away from
us!

• Measure spectrum of galaxies and compare to
  laboratory measurement
• lines are shifted towards red
• This is the Doppler effect Red-shifted objects
  are moving away from us

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The Universe expands!

• Where was the origin of the expansion?
• ?Everywhere!
• Every galaxy sees the others receding from it
  there is no center

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Conclusions from our Observations

• The Universe has a finite age, so light from very
  distant galaxies has not had time to reach us,
  therefore the night sky is dark.
• The universe expands now, so looking back in time
  it actually shrinks until?
• ?Big Bang model The universe is born out of a
  hot dense medium
• 13.7 billion years ago.

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How does the expansion work?

• Like an explosion (hot, dense matter in the
  beginning), but space itself expands!
• Slowed down by gravitational attraction
• Attraction is the stronger, the more mass there
  is in the universe
• Scientifically described by Einsteins
• General theory of Relativity (1915)

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General Relativity ?! Thats easy!

Rµ? -1/2 gµ? R 8pG/c4 Tµ?
OK, fine, but what does that mean?

• (Actually, it took Prof. Einstein 10 years to
  come up with that!)

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The Idea behind General Relativity

• In modern physics, we view space and time as a
  whole, we call it four-dimensional space-time.
• Space-time is warped by the presence of masses
  like the sun, so Mass tells space how to bend
• Objects (like planets) travel in straight lines
  through this curved space (we see this as
  orbits), so
• Space tells matter how to move

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Still too complicated?

• Here is a picture Sun
• Planets orbit

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Effects of General Relativity

• Bending of starlight by the Sun's gravitational
  field (and other gravitational lensing effects)

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What General Relativity tells us

• The more mass there is in the universe, the more
  braking of expansion there is
• So the game is
• Mass vs. Expansion
• And we can even calculate who wins!

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The Fate of the Universe determined by a single
number!

• Critical density is the density required to just
  barely stop the expansion
• Well use ?0 actual density/critical density
• ?0 1 means its a tie
• ?0 gt 1 means the universe will recollapse (Big
  Crunch) ? Mass wins!
• ?0 lt 1 means gravity not strong enough to halt
  the expansion ? Expansion wins!
• And the number is ?0 1

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The Shape of the Universe

• In the basic scenario there is a simple relation
  between the density and the shape of space-time
• Density Curvature 2-D example Universe
  Time Space
• ?0gt1 positive sphere closed,
  bound finite
• ?01 zero (flat) plane open, marginal
  infinite
• ?0lt1 negative saddle open, unbound
  infinite

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The size of the Universe depends on time!
Expansion wins!
Its a tie!
Mass wins!
Time
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So, how much mass is in the Universe?

• Can count all stars, galaxies etc.
• ? this gives the mass of all bright objects
• But there is also DARK MATTER

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Bright Matter

• All normal or bright matter can be seen in
  some way
• Stars emit light, or other forms of
  electromagnetic radiation
• All macroscopic matter emits EM radiation
  characteristic for its temperature
• Microscopic matter (particles) interact via the
  Standard Model forces and can be detected this way

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First evidence for dark matter The missing mass
problem

• Showed up when measuring rotation curves of
  galaxies

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Is Dark Matter real?

• It is real in the sense that it has specific
  properties
• The universe as a whole and its parts behave
  differently when different amounts of the dark
  stuff is in it
• Good news it still behaves like mass, so
  Einsteins cosmology still works!

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Properties of Dark Matter

• Dark Matter is dark at all wavelengths, not just
  visible light
• We cant see it (cant detect it)
• Only effect is has it acts gravitationally like
  an additional mass
• Found in galaxies, galaxies clusters, large scale
  structure of the universe
• Necessary to explain structure formation in the
  universe at large scales

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What is Dark Matter?

• More precise What does Dark matter consist of?
• Brown dwarfs?
• Black dwarfs?
• Black holes?
• Neutrinos?
• Other exotic subatomic particles?

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Back to Expansion of the Universe

• Either it grows forever
• Or it comes to a standstill
• Or it falls back and collapses (Big crunch)
• In any case Expansion slows down!

Surprise of the year 1998 (Birthday of Dark
Energy) All wrong! It accelerates!
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Enter The Cosmological Constant

• Usually denoted ?0, it represents a uniform
  pressure which either helps or retards the
  expansion (depending on its sign)

• Physical origin of ?0 is unclear
• Einsteins biggest blunder or not !
• Appears to be small but not quite zero!
• Particle Physics biggest failure

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Effects of the Cosmological Constant

• Introduced by Einstein, not necessary
• Repulsive ? accelerates expansion of universe

Hard to distinguish today
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Triple evidence for Dark Energy

• Supernova data
• Large scale structure of the cosmos
• Microwave background

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Microwave Background Signal from the Big Bang

• Heat from the Big Bang should still be around,
  although red-shifted by the subsequent expansion
• Predicted to be a blackbody spectrum with a
  characteristic temperature of 2.725 Kelvin by
  George Gamow (1948)
• ? Cosmic Microwave Background Radiation (CMB)

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Discovery of Cosmic Microwave Background
Radiation (CMB)

• Penzias and Wilson (1964)
• Tried to debug their horn antenna
• Couldnt get rid of background noise
• ? Signal from Big Bang
• Very, very isotropic (1 part in 100,000)

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CMB Heres how it looks like!
Peak as expected from 3 Kelvin warm object
Shape as expected from black body
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Maybe pigeons?

• Proposed error pigeon crap in antenna
• Real reason a signal from the Big Bang

Pigeon trap
? Horn antenna
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Latest Results WMAP(Wilkinson Microwave
Anisotropy Probe)

• Measure fluctuations in microwave background
• Expect typical size of fluctuation of one degree
  if universe is flat
• Result
• Universe is flat !

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Experiment and Theory
Expect accoustic peak at l200 ? There it is!
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Supernova Data

• Type Ia Supernovae are
• standard candles
• Can calculate distance
• from brightness
• Can measure redshift
• General relativity gives us distance as a
• function of redshift for a given universe
• Supernovae are further away than
• expected for any decelerating (standard)
• universe

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Supernova Data
magnitude
redshift
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Pie in the Sky Content of the Universe
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Dark Energy Dark Matter SM Matter
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• ?We know almost everything about almost nothing!

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Properties of Dark Energy

• Should be able to explain acceleration of cosmic
  expansion ? acts like a negative pressure
• Must not mess up structure formation or
  nucleosynthesis
• Should not dilute as the universe expands ? will
  be different of content of universe as time
  goes by

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Threefold Evidence

• Three independent measurements agree
• Universe is flat
• 30 Matter
• 70 dark energy

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Measuring Dark Energy
Dark energy acts like negative pressure, and is
characterized by its equation of state, w
p/? ? We can measure w!
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Conclusion

• Cosmology is one of the most exciting subfields
  of physics these days
• The is an intimate connection between cosmology
  and particle physics
• We live in a golden age of cosmology lots of
  data available and being measured
• Todays era is that of precision cosmology
• There is lots we dont know ? interesting for
  young scientists!

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The Night Sky in April

• Nights still long, but EDT gt later observing!
• Spring constellations are up Cancer, Leo, Big
  Dipper
• Saturn dominates the evening, Jupiter early
  morning.

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Moon Phases

• Today Waxing Crescent 34
• 4/5 (First quarter Moon)
• 3/ 13 (Full Moon)
• 3 / 20 (Last Quarter Moon)
• 3 / 27 (New Moon)

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Today at Noon

• Sun at meridian, i.e. exactly south

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10 PM

• Typical observing hour, early March
• Jupiter
• Saturn

Mars Moon
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Zenith

• Big Dipper points to the north pole

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West

• Perseus and
• Auriga
• with Plejades and the Double Cluster

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West

• The Winter Constellations
• Orion
• Taurus
• Canis Major
• Gemini
• Canis Minor

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South-West

• Saturn near Praesepe, an open star cluster

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South

• Spring constellations
• Leo
• Hydra

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East

• Canes Venatici
• M51
• Coma-Virgo Cluster
• Globular Star Clusters
• M3, M5

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East

• Virgo and
• Coma
• with the Virgo-Coma galaxy cluster

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Virgo-Coma Cluster

• Lots of galaxies within a few degrees

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M87, M88 and M91
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East

• Hercules
• Corona
• Borealis
• Bootes

• Globular Star
• Clusters
• M 3
• M 13
• M 92

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M13 Globular Cluster
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Mark your Calendars!

• Next Starry Monday May 1, 2005, 8 (!!!) pm
• (this is a Monday
  )
• Observing at Prairie Oaks Metro Park
• Friday, May 5, 900 pm
• Web pages
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Obs.)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

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Mark your Calendars II

• Physics Coffee is every Wednesday, 330 pm
• Open to the public, everyone welcome!
• Location across the hall, Science 256
• Free coffee, cookies, etc.