Planetariums: Beyond the naked eye

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Planetariums Beyond the naked eye
Seeing beyond the naked eye in a planetarium
Tony Fairall, University of Cape Town/Iziko
Planetarium
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Problems with the human eye

• Insufficient aperture
• Limited wavelength response
• Stereoscopic vision limited to distances lt25 m

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The naked eye view of the night sky is a very
shallow view of the universe
Even without city lights, the human eye has a
very limited view of our Galaxy
CreditInternational Dark Sky Association
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Seeing the galaxy
In a planetarium, the Milky Way can be enhanced
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Axel Mellingers Milky Way panorama
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A portion of Axel Mellengers Milky Way,
with brighter stars removed
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Three panels of a six-panel all-sky projection
Brighter stars are provided by the conventional
planetarium projector
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We can also show the sky at wavelengths the
eye can normaly not register, for example the
radio sky
Radio view of the Milky Way
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Extragalactic sky
And the extagalactic sky
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• Chromostereoscopy
• with false-colour coding
• allows one to depict the universe
• in three dimensions

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Sample panel for 6-projector all-sky system
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Visualisations of extragalctic spaceand
large-scale structures

• Using Labyrinth software developed by
• Carl Hultquist and Samesham Perumal
• Departments of Computer Science
• University of Cape Town

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An introduction to Labyrinth

• This software allows one to visualise a galaxy
  database from any chosen position, looking in any
  chosen direction. One can also interactively fly
  around the database (although the presentation
  here uses still frames).

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Lets start by looking at some data with the
galaxies Represented as white points
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The readouts in the lower left corner give
direction of view and position in Cartesian
Supergalactic coordinates
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Labels can be turned on to identify features
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Colour coding can be introduced to represent
distance. Nearest galaxies red, distant galaxies
blue
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This enables a steroscopic view of the
distribution using ChromoDepth spectacles
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But instead of this distracting false colour
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..we change the coding to white (near) to blue
(far), which works with or without spectacles
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Labyrinth also lets us fade background structures
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Now we see only the nearest galaxies, which can
also be shown ..
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..as billboards, with images to scale, so
giving a realistic visualisation of extragalactic
space.
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But the main purpose of Labyrinth is to grow
Tully bubbles around groups and clusters of
galaxies
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The bubbles can be made completely opaque
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The individual galaxies need not be shown
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The Software identifies Minimal Spanning Trees
(MSTs) and wraps a surface around them.
A minimum number of galaxies per MST can be
specified
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The MSTs are specified by a percolation radius
(r) At cz 0
To compensate for the diminishing density of data
with increasing redshift, the percolation radius
is increased with incresing cz. In this way the
average density of bubbles stays more or less
constant with increasing distance
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As the bubbles grow, they interconnect to reveal
the web of large-scale structures
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We begin by taking 6dF data with cz lt 7500
km/s so to examine very nearby large-scale
structures.
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The view is looking back from a point at cz
20000 km/s in the direction of the North
Celestial Pole
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Northern Galactic Hemisphere at top
Southern Galactic Hemisphere at bottom
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Now to switch on the colour coding
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True stereoscopy can be obtained by viewing these
images With ChromoDepth spectacles
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Individual galaxies
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Mimimal spanning trees show the densest regions
in the data
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The percolation distance r is set at 5 km/s
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The minimum number of galaxies per MST is set at
10
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As we increase the percolation distance, so the
structures grow. Here it is r 10 km/s
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r 20 km/s
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r 30 km/s
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r 40 km/s
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r 50 km/s
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r 60 km/s
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r 70 km/s
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Much more detail can be seen than was
previously possible
r 80 km/s
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r 90 km/s
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r 100 km/s
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Various features can be identified
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We can also blur the large-scale structures
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And gradually bring back the individual galaxies
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Galaxies and Large-scale structures
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Now lets bring in the complete 6dF data
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Labyrinth can also be used to find groups and
clusters, by constraining the size of the
percolation distance and stoping it varying with
distance
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100 k/s
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Decreasing the percolation finds the denser
clusters
75 km/s
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50 km/s
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For example, Labyrinth finds and list just over
100 clusters here. About two-thirds of them are
Abell clusters
40 km/s
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Alternatively, Labyrinth maps large-scale
structures
r 5 km/s
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on an ever larger scale
r 10 km/s
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r 20 km/s
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r 30 km/s
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r 40 km/s
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r 50 km/s
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r 60 km/s
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r 70 km/s
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r 80 km/s
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r 90 km/s
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6dF reveals texture more detailed than ever seen
before!
r 100 km/s
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• Thanks to Matthew Colless,
• Heath Jones and Lachlan Campbell for access to
  the 6dF data