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A new view of the Universe VII Fred Watson, AAO
April 2005
A new view of the Universe VII Fred Watson, AAO
April 2005
In the Universe, things aren’t always what they seem…
…in fact, they hardly ever are!
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
Stellar parallax
Earth
Earth 6 months later
Star appearsto move against
background
Sun
Building-blocks of illusion…
A fixed vantage-point
You arehere
Building-blocks of illusion…
Natural sensitivity only to visible light
Building-blocks of illusion…
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
Finite speed of light
The Moon IllusionThe Moon Illusion
Spot the Moon…
What’s that besideyour head, Liam?
Only my lovefor you, my sweet.
Oh, Yukkk!!!
Our perception of the sky—not a hemisphere, but an inverted dish
Are we at the centre of our Galaxy?
Are we at the centre of our Galaxy?
The Milky Way—relatively uniform.
Are star-counts telling the truth?
No—they ignore the presence of dust
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 Galaxy—no dust
• In 1919, Shapley measured their distances from the Sun
Deductions: we are in the galactic suburbs—and the Galaxy is much bigger than anyone
thought
The Galaxy’s haloof globular clusters
We have a clearer viewof the halo than the disk
SupernovaeSupernovae
Vela supernova remnant
Supernova 1987aphotographed 6 Feb 1989
Supernova Light Echo
Earth
Dust cloud
SupernovaD
a
D = 0.34 a2 / T
Supernova Light Echo
Earth
Supernova
Dust
sheets
What puts the spirals into spiral galaxies?
What puts the spirals into spiral galaxies?
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, we’d expect about 50 turns.
The galaxy would look like a clock spring.
This density wave triggers star-formation, producing masses of hot bright stars that reveal its position.
The spiral arms are an illusion.They trace the passage of a ‘sound wave’ through the disk of the galaxy
Faster than light?Faster than light?
Many radio-objects have expanding lobes
This is a double-lobed radio galaxy, observed with the ATNF, super-imposed on a visible-light photograph.
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.
Faster than light…?
Jets moving outwardsat very nearly the speed of light
To Earth
By the time the jet reachesHERElight from the outburst is onlyHEREgiving the appear-ance from Earth of material moving atsuperluminalvelocity.
Gravity’s lensGravity’s lens
The discovery of gravitational lenses
In the late 1970s, astronomersstarted to discover
‘double quasars’
Shortly afterwards, strange arcs of light were discovered, often
near faint galaxies.
Gravitational lensing
An Einstein Ring…
B0047-2808: zlens = 0.485; zsource = 3.595
Gravitational lens in Abell 2218
Is there a Cosmic Illusionist?
Is there a Cosmic Illusionist?
The laws of physics create the illusions…
but they also allow us to see behind them!
The EndThe End