The Cosmic Distance Ladder

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The Cosmic Distance Ladder
Dr. Frederic V. Hessman Universitäts-Sternwarte
Göttingen
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The Importance of Distance

• The only direct forms of information we have from
  cosmic objects are
• Light (frequency, amount, velocity, color,
  chemical abundances)
• Position on Sky (angles, movement)
• Time (temporal variations)
• Everything else has to be derived from these few
  hints, e.g.
• Mass (velocity, time, sometimes distance)
• Power (amount, distance)
• Size (angle, distance)
• Age (different quantities, distance for
  cosmological objects)

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The Distance Ladder
External Galaxies
Our Galaxy
Solar System
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Within the Solar System
Johannes Kepler
Radar
Astronomical Unit
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Stellar Parallaxes
Parallax
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Cepheid Variable Stars
Brightness
Velocity
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SUPERNOVAE
Brightness
Time
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Cosmic Expansion (Hubble Flow)
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The Basic Distance Ladder
Type Ia Supernovae (Thursday)
External Galaxies
Cepheid Variables (Wednesday)
Our Galaxy
Geometrical Parallax (Tuesday)
Solar System
Astronomical Unit (Monday)
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I The Distance to the Sun
Eratosthenes (235 B.C.E.) accurate size of the
Earth Aristarchus (210 B.C.E.) relative sizes
Earth and Moon
Kepler (1630) connection between orbit size
and period Cassini Richter (1672) triangulatio
n distance to Mars Halley (1761,
1769) triangulation of Venus transits
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One Way to Measure the Distance

• Measure angular radius of Sun w
• Measure rotation period P
• Measure rotation velocity V
• V 2?R / P
• sin(w) R / AU

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Measuring the Angular Radius
Pin-Hole Camera
w
l
L
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Measuring the Suns Rotation Rate
Sunspots
Angle
Time
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Measuring the Suns Rotation Speed
Doppler Effect ??/?V/c
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Corrections

• Size of Pin-hole w
• Projection of solar rotation to the equator P
• Earths orbital (synodic) motion P
• Sun Earth velocities not perpendicular V
• Suns rotational axis tilted by 6.46 deg V

(See Page 9)
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One Way to Measure the Distance

• Measure angular radius of Sun w
• Measure rotation period P
• Measure rotation velocity V
• V 2?R / P
• sin(w) R / AU

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What else can one do with the A.U.?
(See examples on Pages 12 13)
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What else can one do with the images?
http//www.kis.uni-freiburg.de