Patterns in the Sky

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Patterns in the Sky Constellations
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Dont be fooled by what you see!

• The sun and the moon appear to be the same size
  in the sky (0.5 degrees)
• Alpha Centauri appears to be much dimmer than the
  Sun
• Alpha Centauri and Vega appear to be equally
  bright
• Are you upside down?

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Think!

• The moon and the sun COULD be at different
  distances
• Alpha Centauri and Vega COULD be different types
  of stars
• YOU could be upside down!
• The apple COULD attract the Earth with the same
  force
• ? Expand your universe!

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Top Down

• The Universe is accelerating its Expansion
• How do we know?
• Supernovae are dimmer than they should be in a
  standard expanding universe
• What is a supernova? What is a standard universe?
• SN are massive stars exploding at the end of
  their lives
• How do we know?

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Top Down

• Stars are hot gas balls that fuse H to He they
  run out of fuel
• How do we know?
• Can measure spectra, compare to the sun
• What is a spectrum? How does the sun work?
• The sun is 300,000 more massive than the earth,
  consists of H He, produces a lot of energy ?
  must be fusion
• How do we know?

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Top Down

• Measure distance to sun, use Newton gravity to
  obtain mass, measure H He spectra in lab
• How do we measure distance to sun?
• What is Newton gravity?
• What are spectra in the lab?
• Use Keplers laws, observe special configuration
  of planets from different positions on earth
• What are Keplers laws? How big is Earth?

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Top Down

• Planets go around the sun in ellipses
• How do we know?
• The observers view is different for different
  places on Earth ? radius
• How do we know
• ?Look at the sky!

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What is Astronomy?

• The science dealing with all the celestial bodies
  in the Universe
• Cosmology is the branch of astronomy that deals
  with the cosmos, or Universe as a whole
• The medieval list of the Liberal Arts grammar,
  rhetoric, logic (trivium) arithmetic, music,
  geometry and astronomy (quadrivium)
• Is an exact science for 5000 yrs
• Most rapid advancements in astronomy have
  occurred during the Renaissance and the 20th
  century
• Success has been a result of development and
  exploitation of the scientific method

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Why study Astronomy?

• Practical reasons seasons, tides, navigation,
  space technology, satellite communication
• Idealistic reasons cosmological questions
  (Where do we come from?), aesthetics, curiosity
• Two things fill the mind with ever new and
  increasing admiration and reverence, the more
  frequently and enduringly the reasoning mind is
  occupied with them the star spangled sky over me
  and the moral law in me. (I. Kant)

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Astronomy and Culture

• Astronomy had and has an enormous influence on
  human culture and the way we organize our lives
• For example
• The year is the rotation period of the Earth
  around the Sun
• The year is subdivided into months, the period of
  the Moon around the Earth
• The weeks seven days are named after the seven
  bodies in the solar system known in antiquity
  Sunday, Monday, Saturday (obv.), TuesdayMardi,
  Wednesday Mercredi, ThursdayJeudi,
  FridayVendredi

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Our vantage point Earth
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Basic Observations in Astronomy

• We see (on clear days!)
• A very bright disk that is up about 12 hours. It
  comes up in a specific direction, rises higher
  until it reaches a maximal altitude in a second
  direction, then sinks lower until disappearing in
  a direction opposite of the direction where is
  came up
• A less bright object that changes its appearance
  and is also up for a (different) duration of 12
  hours. Same rise/set pattern as very bright
  object.
• When the very bright disk is not visible, we see
  many tiny specs of light of different brightness
  and color

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Basic Observations in Astronomy

• We see further
• The tiny specs move across the sky as the hours
  go by. One group moves across the sky in 12
  hours. Same rise/set pattern as bright object.
• The position of the specs wrt other specs is
  fixed, but they move wrt to the ground
• Careful observation reveals a handful of
  exceptions from this rule
• some bright specs move slowly wrt to the other
  fixed specs, and also are visible 12 hours. Same
  rise/set pattern as bright object.
• One spec sits at the center of this motion and
  does not move

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Conventions

• These patterns repeat every day, lets name them
• Sun
• East, South, West
• Moon
• Daytime Nighttime Day (needs to be revisited
  later!)
• Planets
• Polaris, the North Star

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More names, now that weve seen

• Observer Coordinates
• Horizon the plane you stand on
• Zenith the point right above you
• Meridian the line from North to Zenith to south

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Hypothesis

• During a day, it looks like all lights in the
  sky travel around us, like the are fixed to an
  (invisible) sphere that turns around us.
• Call it The Celestial Sphere

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Further Observation

• If we move to a new observing place on Earth, the
  pattern remains the same (bright light rises
  sets, etc.), but
• Position of North Star changes
• Maximal altitude of Sun, special stars changes

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Conclusion Earths coordinates projected onto Sky

• The Celestial Sphere
• An imaginary sphere surrounding the earth, on
  which we picture the stars attached
• Axis through earths north and south pole goes
  through celestial north and south pole
• Earths equator ?
• Celestial equator

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Celestial Coordinates

• Earth latitude, longitude
• Sky
• declination (dec) from equator,/-90
• right ascension (RA) from vernal equinox, 0-24h
  6h90
• Examples
• Westerville, OH 40.1N, 88W
• Betelgeuse (a Orionis) dec 7 24
  RA 5h 52m

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Confusing! Lets go with Patterns in the Sky!

• We can group specs of light together to form
  triangles, squares, etc.
• This allows us to find them the next night and
  follow their motion
• Talk to other observers, and give them names
  Bear, Bull, Lion, Hunter, Queen, etc.
• ? The Constellations

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Constellations of Stars

• About 5000 stars visible with naked eye
• About 3500 of them from the northern hemisphere
• Stars that appear to be close are grouped
  together into constellations since antiquity
• Officially 88 constellations
  (with strict boundaries for
  classification of objects)
• Names range from mythological (Perseus,
  Cassiopeia) to technical (Air Pump, Compass)

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Constellation 1 Orion

• Orion as seen at night Orion as
  imagined by men

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Orion from the side

• ?Stars in a constellation are not connected in
  any real way they arent even close together!

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Constellation 1 Orion

• the Hunter
• Bright Stars
• D) Betelgeuze
• E) Rigel
• Deep Sky Object
• i) Orion Nebula

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Constellation Gemini

• the Twins
• zodiacal sign
• Brightest Stars
• I) Castor
• JK) Pollux