Instrumentation for Cosmology

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A new view of the Universe VII Fred Watson,
AAOApril 2005
Cosmic Illusions
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In the Universe, things arent always what they
seem

• in fact, they hardly ever are!

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Building-blocks of illusion

• Natural (stereoscopic) depth perception is
  limited.
• Understanding Solar System dynamics extends our
  perception of depth to more than 10 billion km.
• Stellar parallax extends depth perception to a
  thousand or so light-years.

A 2-dimensional view of the sky
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Stellar parallax
Earth
Sun
Star appears to move against background
Earth 6 months later
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Building-blocks of illusion

• A fixed vantage-point

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Building-blocks of illusion

• Natural sensitivity only to visible light

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Building-blocks of illusion
Finite speed of light

• Lookback times
• Moon 1.3 seconds
• Sun 8 minutes
• Jupiter (this evening) 35 minutes
• Nearest star 4.2 years
• Large Magellanic Cloud 165,000 years
• Andromeda Galaxy 2.2 million years

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The Moon Illusion
Cosmic Illusions
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Spot the Moon
Only my love for you, my sweet.
Oh, Yukkk!!!
Whats that beside your head, Liam?
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Our perception of the skynot a hemisphere, but
an inverted dish
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Are we at the centre of our Galaxy?
Cosmic Illusions
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The Milky Wayrelatively uniform.
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Are star-counts telling the truth?
Nothey ignore the presence of dust
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Globular clusters

• About 150 known in our Galaxy
• Most are in one part of the sky (Sagittarius)
• Many are above or below the plane of the
  Galaxyno dust
• In 1919, Shapley measured their distances from
  the Sun

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Deductions we are in the galactic suburbsand
the Galaxy is much bigger than anyone thought
The Galaxys halo of globular clusters
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Supernovae
Cosmic Illusions
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Vela supernova remnant
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Supernova 1987aphotographed 6 Feb 1989
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Supernova Light Echo
Earth
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Supernova Light Echo
Dust
sheets
Earth
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What puts the spirals into spiral galaxies?
Cosmic Illusions
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What are the spiral arms?
Just strings of stars? No, because they would be
tightly wound up. Suppose the age of the galaxy
is 10 billion years. Its inner regions rotate
once in 200 million years Therefore, wed expect
about 50 turns. The galaxy would look like a
clock spring.
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The spiral arms are an illusion. They trace the
passage of a sound wave through the disk of
the galaxy
This density wave triggers star-formation,
producing masses of hot bright stars that reveal
its position.
Found in Space
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Faster than light?
Cosmic Illusions
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Many radio-objects have expanding lobesThis is
a double-lobed radio galaxy, observed with the
ATNF, super-imposed on a visible-light photograph.
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Twin jets of material from a binary star in our
Galaxy The expansion took place during the
course of a few days in late-1997.
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Faster than light?
By the time the jet reaches HERE light from the
outburst is only HERE giving the appear- ance
from Earth of material moving at superluminal vel
ocity.
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Gravitys lens
Cosmic Illusions
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The discovery of gravitational lenses
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Gravitational lensing
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An Einstein Ring

• B0047-2808 zlens 0.485 zsource 3.595

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Gravitational lens in Abell 2218
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Is there a Cosmic Illusionist?
Cosmic Illusions
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The laws of physics create the illusions
but they also allow us to see behind them!
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Cosmic Illusions
The End