DEAR ABBE: What’s with the “twinkle” in this Hubble image?


the Spirit of Ernst Abbe
Legendary physicist Ernst Abbe answers your photonics questions

DEAR ABBE: I was cruising around the internet the other day in my web-rocket when I came across this stellar image of the comet ISON, taken by the Hubble space telescope. The stars appear to be twinkling. I was under the impression that the twinkling effect we see on earth is due to the atmosphere, and last time I checked the Hubble was something of a space telescope, so shouldn’t Hubble be above twinkling? -HUMBLED BY HUBBLE

DEAR HUMBLED: You’re right about twinkling, it is not apparent to observers located outside of a dense atmosphere, the topic of the 1969 paper “Importance of observation that stars don’t twinkle outside the earth’s atmosphere” by astronaut Walt Cunningham and co-author L. Marshall Libby. But twinkling is not likely to produce such picturesque points on stars as you see in that Hubble image. Rather, what appears to the naked eye as twinkling will serve to blur and smudge the image of a star in a time-averaged intensity measurement, such as a photograph.


The spikes you see in the image in question are due to something else entirely. Twinkling stars are a result of a fickle refractive media, the atmosphere, inadvertently being included in an imaging system. The culprits causing these spikes are intentionally built into the optical system, though the effect on the image formed is a byproduct of their form rather than their primary function. What you see as four regular points oriented to the same direction on every bright star is actually the result of diffraction around the secondary mirror support struts[2][3]. Since the spikes are the Fourier transform of the struts themselves[4], they will affect every light source in the image according to their shape and brightness. The appearance of diffraction spikes is so common that the human mind essentially expects it in this type of image, and can be considered aesthetic. Ultimately, though, any light ending up in the diffraction spikes is light that could have contributed to forming the accurate image of the scene. If a dim object of interest resides by a very bright point of light, the diffraction spikes of the latter can interfere with the clear few of the dim object.

Hubble’s successor, the James Webb telescope will have three struts rather than four[5], resulting in a very different set of diffraction spikes. Not only will the James Webb struts differ in number, but these will be arranged in a sort of triangular pyramid. Diffraction around the strut will affect the final image differently at different lengths along each strut, because they will occupy a range of distances from the primary mirror. The resulting spikes should be quite interesting.

Comet ISON image available at

Do you have a question for Abbe? Ask it in the comments or tweet it @theScinder

Referencing “I Fucking Love Science” in Your Article Title is a Great Way to Attract Web Traffic

Negging your audience is also important, apparently.


John Skylar had an interesting article last week, picked up by Mashables shortly after it went a bit viral. He points out that the beautiful images posted on I Fucking Love Science (hereafter referred to as IFLS) are not all that great of a representation of what science is, and fawning over them does not equate a “love of science,” (though I would argue that stock photography of people pipetting is also “not science”). After I point out that Skylar’s seemingly hostile position on IFLS was actually just an aggressive technique for internet-writers to drive traffic, I want to quickly defend IFLS for what it actually provides. IFLS is what science students, profs and professionals would refer to as their outreach work: it drives interest and awareness among the general populace, many who would never be exposed to it otherwise. For those working in scientific fields, it provides a window into other fields as well. Usually the image is accompanied by a short explanatory text and a link to the original article, or at least the popular press take on it. I would expect that the nominal goal for outreach, not just IFLS, is to increase scientific literacy in the general population. But once again there is a pervasive conflation of terms, and it isn’t confusing data with people and money, it is conflating results with a method. I would claim that in actuality, Mythbusters is potentially better for improving scientific literacy than IFLS, and zombie Richard Feynman would back me up.

I studied science and engineering at the undergraduate and graduate level for about five years, doing a little research along the way to boot. In all of my coursework, I can’t recall taking a single class that actually taught science. The coursework that probably came the closest was in statistics. In lieu of teaching a few courses a year on the intricacies of the scientific method, elegant experiments, etc., courses in a science department almost invariably teach the history and current consensus of a field, by and large treating this information as static facts. In short, they focus on the results and tend to ignore where these results come from. The contents of the science coursework taught at a typical university is not science, it is trivia.

Science is a method for figuring out if an idea we have about the world is false, nothing more. You have heard this before if you ever competed in the science fair as a kid. Science is a comparison of guesses and givens, where guesses are the results we expect if some idea we have about the world might be true. Givens are the data, gathered by observations, measurement, and sometimes assumption. Where the guesses and the givens don’t agree, the original idea is WRONG, simple as that. The best science is based on the ideas that are most readily falsifiable, not necessarily the most complicated. A vague theory is hard to disprove, but it still can be very, very useless.

Ultimately, scientific literacy is not knowing how many flarks jive a phoouon with a 90 rad spin, but the ability to be confronted with a claim and confer upon it a vote of confidence or no confidence in that idea’s reality. The best way to love science is to use it to inform your view of the world, regardless of your profession. Next time another human tries to sell you on an idea, ask to see their p-value, and don’t trust averages without error bars. If you start with an unsparing application of science, the survival rates of nonsense will plummet. Maybe that effect would even trickle up to the higher echelons of U.S. government, and eventually they might enact reasonable policies with an outlook beyond four years at a time, including emphasising a strong and stable investment in academic research.

Hat tip to Neal Stephenson’s novel Anathem for influencing my interpretation of “givens.”

Feynman has the best description of science that I have yet found.

Image from originally from the book “Mendel’s Principles of Heredity: A Defence.” Scans of book at

Stop Saying Dynamical


Following close behind experimental testing of falsifiable hypotheses, the secondary responsibility of a scientist is arguably clear communication of results. Given that the majority of research is ultimately funded by the tax-paying public, it is important that outcomes are eventually conveyed in a manner that can be understood by an intelligent layperson. Increased scientific literacy in policy makers and their constituents is a prerequisite to face modern challenges such as changing climate, public health, and the consequences of population pressure. Effective outreach to the public is more important than ever. Accepting the previous statement, why is there a continuing trend among scientists to mask communicative content through cryptic language, particularly when perfectly acceptable and widely recognized terms are available? I’ll focus on what I consider to be the most obvious and ridiculous offender, the great scourge of scientific writing, faculty information pages, and grant proposals; the great occluder of meaning, intimidator of readers, the entirely redundant bit of lexicon: dynamical.

Dynamical, like its more accessible and less attention-hungry sibling word dynamic, has its roots in the Greek dynamikos, meaning powerful. In general both terms relate to something that changes with time. Since both “dynamical” and “dynamic” function as adjectives, they are essentially interchangeable, the only difference between that I have ever been able to discern is the demographics of their use. “Dynamical” is used by physicists, mathematicians and engineers who work in dynamical systems theory, a branch of mathematics dealing with systems described by differential (if continuous) or difference (if discrete) equations. The additional suffix “-al” that delineates the two words seems to have been born of single, somewhat malicious intent: to serve as brick and mortar in the construction of an ivory tower separating scientists and small-folk. It is exactly this sort of word choice that leads to the perception that scientists have more smarts than sense and that they produce results that ultimately fail to have any application to the real world. Ultimately this serves as fuel for the anti-science fire burning through the minds of policy makers and the public. Consider the following two sentences and the impression they would leave on a reader over a morning coffee:

“We utilize the time-slice method as a means of dynamical downscaling to specify expected climate change for Southern Europe”

“We utilize the time-slice method as a means of dynamic downscaling to specify expected climate change for Southern Europe”


U. Cubaschll, H. von Storch, J. waszkewitz, E. zorita. Estimates of climate change in Southern Europe derived from dynamical climate model output . Climate Research . November 29 , 1996.

Even though the sentence makes reference to specific methods that a non-specialist reader might not be familiar with, the language is descriptive enough to impart a conceptual understanding of what the authors describe, except for that cumbersome “dynamical,” which throws the whole thing into question. It reads as if it came from a humour piece poking fun at absent-minded professor types. The null-meaning suffix implies there is meaning above and beyond the root word where there is none, it just sounds more complicated. This is not an outcome that scientists should strive for, no matter how intelligent it makes them feel to use it.

As disciplines in life science become increasingly concerned with complexity and modeling, I expect the number of life scientists interested in studying dynamic systems will only continue to rise. Given the particularly relevant nature of life sciences to understanding our relationship to our living planet, I beg you, wherever possible, to avoid using the word dynamical. The physicists, mathematicians, and engineers may be entrenched in their devotion to the nonsense word, but there’s no reason for this senseless departure from clarity to infect biologists, ecologists, biochemists, etc. any more than it already has. The arbitrary and counterintuitive way that scientists name the genes they discover-a combination of sarcasm, mystery and the opposite of their function-is a big enough mess.


Consider this an invitation to attempt to delineate the dynamic/dynamical word pair in the comments.

Stereographic anaglyph from shift-lens

In thinking about camera arrays, integral photography, and light fields, I began to see the similarities between stereographic photos and those from an array of cameras (or a single camera occupying multiple positions at different times). What sort of depth can be achieved by a moving lens over a stationary sensor? A fair amount, for distances at which the object distance is not >> than the inter-aperture distance between lens positions. The result is below: you’ll need a red/blue pair of filters or glasses to view it. Tilt-(shift) stereograph

A perspective control lens like the one used here is typically used to straighten the “vanishing lines” of tall buildings or features without wasting sensor/film space, and generally for perspective control. The lens I used here was a 35mm f/2.8 Canon FD tilt-shift lens on a Nikon D5100 with a Fotodiox mount/infinity correction adapter, the images were separated by ten lateral ticks as marked on the lens body (these appear to be about a millimetre, but are not labeled). The object distance was approximately ten cm.

Plenoptic imaging on a macro bellows rail


After watching Dr. Marc Levoy’s talk on light fields and the Stanford camera array I thought I’d investigate for myself the uses for synthetic aperture photography. From the talk:

By changing the amount of shift, you can change the depth of objects that are in focus. And here’s what that looks like. So we’re focusing synthetically on the bushes, across the street through my grad students into the building and there’s a step stool in the building.

This is about the same as matching up the left/right channel on a stereo anaglyph, but with more perspectives as inputs. To get a feel for things I drilled out a camera mount to attach to the end of a macro bellows rail and took a series of horizontally displaced images, shifting and combining them in Octave to focus at different depths.
Continue reading “Plenoptic imaging on a macro bellows rail”