Diffraction Star Photos

by rb780nm on May 20, 2014

I was flicking through a photography book while hanging out in Brisbane airport on Sunday night, looking at ‘creative’ photo ideas. I didn’t have much of my camera gear with me – just the one lens and a little tripod… but I found a section on diffraction star effects – photographing the diffraction patterns caused by the edges of the lens aperture.

So I took this series a photos with gradual steps in aperture size.

As the aperture opens up, the diffraction effect becomes smaller. It also rotates slightly as the positions of the blades of the aperture move…

Occultation of Saturn

by rb780nm on May 20, 2014

The other night, Saturn passed behind the Moon. it was visible from my deck, and the sky was clear, so I took a time lapse of it. It’s just with my DSLR and it’s strongest zoom lens, so these aren’t great pictures…

But I wanted to track the moon in this video – it’s time consuming and difficult to crop each frame individually keeping the moon stationary, but I wrote a script in Matlab using the built-in circle finder utility and made this video:

%track moon and crop

fid = fopen(‘file_list.txt’)
files = textscan(fid,’%s’)
foo2 = files{1}
for j = 1:numel(foo2)
files{j} = foo2{j}

hold on

for j = 1:97%numel(files)
rgb = imread(files{j});
[centers,radii] = imfindcircles(rgb,[255 280],’ObjectPolarity’,’bright’,’Sensitivity’,0.92,’EdgeThreshold’,0.1)

rgb2 = imcrop(rgb,[max(centers(1)-400,0),max(centers(2)-400,0),800,800]);


HSC Physics 2013 1-A-1: Dependent and in Independent variables (and experimental design)

February 18, 2014

An investigation is designed to determine the size of the generated current when the strength of a magnet is varied. Which is the independent variable for this investigation   a)    Speed of the Magnet b)   Strength of the magnet * c)    Size of the generated current d)   Distance between the coil and the magnet   […]

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Satellite feature identification: Cyclogenesis

June 11, 2013

Meted: Satellite feature identification: Cyclogenesis Extratropical cyclone developement Cyclones tend to delope along preexisting fronts when an upstream perturbation approaches in the mid- or upper-troposphere. The surface baroclinic zone kinks, creating a cyclonic perturbation. One should look for cyclongesis in the surface baroclinic zone. This region is associated with a frontal band cloud pattern. Cyclogenesis […]

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Notes on Pressure Gradient Force

May 31, 2013

Based on MetEd unit   Pressure Gradient Force The pressure gradient force is not a “force” exactly, but instead is a pressure-related acceleration caused by differences in pressure within a fluid mass, expressed as a force per unit mass. It is directed from higher toward lower pressure. It has both vertical and horizontal components, although […]

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Notes on Jet Streams

May 29, 2013

Based on the Meted unit “Jet Streams” Jet Streams   Near the tropopause, corridors of very strong winds.   Fastest: Polar front jet and Subtropical jet, flow from west to east. There is also a Tropical Easterly Jet in the upper troposphere.   Jets defined where wind speeds exceeds 50 knots (25m/s)   Also lower […]

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Variability in the width of the tropics and the annular modes

May 28, 2013

Kidston et al. Geophysical Research Letters, 2013. It has been observed (Kang and Polvani 2011) that the variability in the location of the edge of the Hadley Cell () is correlated with the latitude of the storm-tracks and surface westerlies (; EDJ is the Eddy Driven Jet), particularly in the Southern Hemisphere during Austral Summer […]

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Notes on Tokinaga et al. 2012

December 2, 2012

Slowdown of the Walker Circulation driven by tropical Indo-Pacific warming. – Slowdown of Walker Circulation is a robust change, observed over the last century – Useful testbed for model evaluation – AGCMs only simulate the reduction of the walker circulation if the correct spatial pattern of SST warming is prescribed. The simulations fail if an […]

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How To Create a Great (Physics) Science Fair Project (and Learn Something at the Same Time)

October 3, 2012

To do well in a science fair, you need to do two things – You need to not only demonstrate knowledge of science, but also knowledge of the process of science. While this can be a daunting task if you’ve never produced a successful science fair project before, you should rest easily – it is […]

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Telling what’s more important

June 7, 2012

Paul Erlich (The Population Bomb) was interviewed on the Nature Podcast this week, and in response to a question of whether population or consumption was more responsible for the threats to the planet, he answered that that was like asking if the width or the length of a rectangle was more important to creating the […]

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