Phys 1830 Lecture 20
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Second Term Test is coming
up Friday Mar 6.
Covers material after previous
test (pseudo-cummulative).
Topics from “how images are
made” (lecture 11) through
“computer simulations”
(coming up).
Check material online for test
information.
Opportunities to study:
AstroClub
1.Today Allen 330 at 3:30pm
Office hour: Today
Allen 514 at 3pm
Upcoming Classes
• Visualization:
– Workshop
– Computer Simulations
• Planetary Systems
– Formation
– Simulations
– Observations
• Our Solar System
• Solar System Formation
Phys 1830: Lecture 20
Bubble Nebula – NGC 7635
summary
Recall column
• Goal: Explore how to construct
a public outreach image.
• Within each public outreach
image is the struggle between
scientific meaning and visual
aesthetic.
Simple Colour Wheels
B is called blue but is purple
(i.e. blue-violet)
R is called red but is orange
(i.e. red-orange)
Goal:
Select colours to make a harmonious final image.
That is, generate a final image with
complementary colours, greys (not browns), at
least one of the 7 contrasts, etc.
Seven Colour Contrasts
Which of these contrasts interest you and your partners?
Seven Colour Contrasts
Fire up GIMP! (Take Notes!)
1. Setup layer file (.xcf)
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Make new file with black background
Copy thumbnails into layers with screen mode
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Copy visible, paste, name, set mode = screen.
black background layer helps reduce noise.
2. Colourize each layer
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Copy layer, turn off original
Use levels tool to select colour in active layer
colour need not be what your eye would see; consider
aesthetics and visual grammar.
3. Adjust colours
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Curve tool
helps reduce noise, increase detail and harmony.
Fire up GIMP!
4. Create single layer file (.tiff)
– Make new file with black background
– Copy visible from .xcf file and anchor, flatten.
5. Adjust colours
– Curve tool
– generate striking images
6. Orient
7. Crop
• both 7 & 8 guide the eye.
8. Cosmetics (remove cosmic rays & noise)
If you are ahead of the class, do a different colour rendition! See if it works better.
Cosmetics
• make unresolved sources white
(layer in a stretched B&W image)
• remove CRs and chip seams in optical images
(clone tool)
Critique --Today
When finished on MONDAY send an email with 3 items
1. Send your jpg images to
[email protected] for the website and
for grading.
2. Include the full names and student numbers of
everyone on your team
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state their attendance for each day (if in attendance it
will be assumed that they participated).
3. BRIEFLY state the following in your email:
• what were your final colours
• what were your final contrasts
• did your image have an appropriate vertical or diagonal element to
retain the viewer’s attention
• how do your results compare to your goals?
Critique – constructive criticism
• Look at the images of your neighbours.
• Discuss with them their original colour and
composition goals. Were they successful?
• Offer suggestions for improvement.
• Did any interesting issues come up?
Lesson 1
• The process of making astronomy images is
iterative. Sometimes one has to go right back
to the stretching.
Lesson 2
• More than one colourization, orientation, etc
is valid.
Compare with other versions:
http://www.physics.umanitoba.ca/~english/vizimagesUVi
c/
http://www.physics.umanitoba.ca/~english/2013fallphys1
830/bwimaging/imagesindex.html
Also who are you representing?
Different versions accordingly.
• Our team’s final colour scheme matched our
original selection.
a)yes
b)no
c) sort of
• Our team’s image showed the supernova
remnant as a distinct object.
a)yes
b)no
c) sort of
Visualization: Simulations
summary
Recall column
• Image-making is part of a larger activity
called Visualization
• Other activities include “computer
simulations”.
• Some of the following slides are modified
versions of those from Dr Chris Fluke at the
Centre for Computing and Astrophysics at
Swinburne University of Technology
(Melbourne, Australia)
• Example of a cosmological simulation
Why We Need Computers
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Great for complex problems
Help improve theoretical models
Enable comparison with observations
"What happens if?” questions
Experimentation in Astronomy
• Observers:
– A sample of one
• Computational Astronomy:
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As many versions as we want!
Make predictions/compare with observations
Statistical results
Search more of parameter space
How DO You Create a Universe?
Assumptions
Cosmological Model
+ Parameters
Simulation Method
Astronomical Society of
Victoria: Computational
Cosmology 2006
Assumptions
• The Universe is a single, very large,
gravitational system
• Properties and dynamics explained by
Einstein’s General Theory of Relativity
• Cosmological Principle: there is nothing special
about our location in the Universe (Milne 1933)
– Homogeneous (looks same to all observers)
– Isotropic (looks same in all directions)
From this…
As universe expands and cools, small primordial
density fluctuations are amplified by gravity
… to this
Treat dark matter &
atoms as collection of
points.
Abell Cluster 2744 (HST)
Cosmological Simulation
1) Parameters:
• Choose cosmological parameters
– Dark Matter, etc.
• Choose simulation parameters:
– Number of “particles” (N)
– Size of simulation box (B)
– Number of time-steps
• Set up initial configuration
Cosmological Simulation
2) Model: Apply Newton’s law of Gravity
3) Simulation Method: the N-Body Simulation
N = 2 (N is the number of bodies)
F= GmM/r
2
v
= GM/r
2
N=3
No exact
solution!
N-Body Solution
i
(N-1) = 12 FORCE
PAIRS
j
N =13 particles
N*(N-1) = 13*12
= 156 FORCE
CALCULATIONS
Resolution is the Name of the
Game
• Ideal:
– N = 100 billion stars in a galaxy
– At least one simulation particle per star
• Current:
– Millennium Simulation (MS)
– http://www.mpagarching.mpg.de/galform/virgo/millennium/
– N = 10 billion particles in a box
– MS-II focuses on smaller volume