Merry Christmas

There was a caveman named 'Ogg' who lived in Waterloo. Everyday, Ogg would drive to his job in Ikea, stopping first in Hamilton to pick up his work colleague, caveman 'Thor'. As the weeks went by, Ogg noticed the rest of the people he worked with were changing. They were becoming taller, their heads looked different and they started wearing more clothes. Eventually, he decided to ask about it.

"Don't you know?" his work colleague replied. "If you commute with a Hamiltonian you don't evolve."


No, this was not in fact an episode of the TV sitcom, 'The Big Bang Theory', but the Physics and Astronomy holiday party. Yes, I found the conformation to stereotypes alarming as well.... I also laughed at that joke. This was even more alarming. It was clearly time for another beer.

For those for whom quantum mechanics has not become part of their humour repertoire, the above joke plays on the name of a maths function called the Hamiltonian that is used to calculate the energy of a system, e.g. a particle attached to a spring. If another property of that system, for instance the amount of rotation it has (angular momentum), does not change as time passes, it is said to 'commute' with the Hamiltonian. Of course, the term 'Hamiltonian' could also mean a person from the city of Hamilton. So our caveman friend Ogg was commuting with the Hamiltonian, Thor, and therefore couldn't change over time or evolve.

... Yeah. The explanation doesn't make it a more excusable joke.

Merry Christmas everyone.

It's life Jim, but ..... 5/6 how we know it

Nov. 29, 2010:

NASA to Hold News Conference on Astrobiology Discovery
Science Journal Has Embargoed Details Until 11 a.m. PST On Dec. 2

It was to be three nail biting days of anxious waiting. Stress levels in scientists across the globe rose to values only previously seen the week before Apple's iPad release. At least half of Oregon packed a suitcase ready to be told alien Spock had made first contact and his buddy Tuvok had a spare room for guests. Kentucky loaded their shot guns.

Then the moment of truth dawned:

There's a bacterium 1/100th of the size of a human hair that hangs out in some pond in California and lives off arsenic.

Whereupon approximately half the audience fell asleep, half went into a state of frenzied excitement and the one person to actually understand its implications commented that this complicated matters. To know exactly why this one person felt this way, we need to understand what makes you and the microbes in your kitchen sink blood brothers.

We have long known that life can exist in some pretty unlikely places. Organisms aptly known as 'extremophiles' have been found to thrive in temperatures exceeding 100°C (hyperthermophiles), in solutions more acidic than lemon juice (acidophiles) and under bombardment of powerful ionising radiation (radioresistent). So while California's Mono Lake with one of the highest concentration of the deadly toxin arsenic on the planet might not make a swim resort, it is perhaps not astonishing that it should still harbour life.

However, the extremophiles, you, me and the microbes in your kitchen sink are all composed of six major elements; carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus, with trace other ingredients as icing to the biological cake. Until the NASA press release, these six fundamental building blocks were common to all forms of known life. In fact, while one could speculate otherwise, there was no evidence that life didn't require these six elements to exist. This meant that searches for life on other planets seemed to necessitate the detection of the presence of these seemingly essential ingredients.

The difference with the bacterium found in Mono Lake is that it is the first living entity to have been discovered that violates this cardinal rule. Instead of phosphorus, this microbe can use arsenic in its DNA. Since phosphorus is vital to cell reproduction, it might be considered a controversial move to substitute it for the second most favourite poison in Agatha Christie's famous crime novels (the first is cyanide, in case anyone was interested). It turns out that arsenic is actually chemically similar to phosphorus, sitting directly below it in the periodic table. This makes it a viable alternative.

The discovery that life can form using a different fundamental base of elements is immensely important for scientists who have been trying to imagine what life on other worlds would be like. However, there is one thing that this discovery is not which, if it were, would cause every astrobiologist in the world to pass out for at least a week.

It is not an unrelated form of life to us.

All currently known forms of life have a common origin. Nevertheless, it is possible to conceive that life might develop in multiple places on Earth independently of one another. An occurrence of a second genesis of life on Earth is known as a 'shadow biosphere' and could evolve in a completely different way to life that we know. If such a system were found, it would be evidence that life is not difficult to produce in the right conditions. That being so, it would increase the odds of life being present on other planets considerably.

Basically, it would be time to check that your best friend isn't from a small planet somewhere in the vicinity of Betelgeuse.

The case of the bacterium in Mono Lake is not a shadow biosphere. While this microbe can use arsenic, it can also use phosphorus and indeed will prefer to when given the choice. Moreover, Mono Lake has only become heavy in arsenic over the last 50 years. Prior to that, it had a source of fresh water, removing the environment in which an arsenic-dependent microbe could develop. This points to an organism that originally conformed to the established six building blocks of life, but evolved to survive in the increasingly hostile environment of Mono Lake.

While it may not be a new form of life, this tiny microbe opens the door to a huge number of questions in astrobiology. It particular, its discovery proves that we will have to be significantly more open minded when searching for life outside our planet. If there is no core pattern that nature cannot adapt when required, then what signatures can we design our detectors to search for? In fact, this microbe hasn't so much as opened a door as ripped it off its hinges.

References: the original paper for this research is science.1197258. There are also two excellent reviews at 'Not Rocket Science' and 'Bad Astronomy'.

When stars collide

"I have a visitor, Fabio Antonini, from the Rochester Institute of Technology who is here to work on the evolution of stellar collisions."

The email from Evert Glebbeek, a postdoc in the department working with Alison Sills, popped into my inbox and nearly made me pop out my chair. What did he mean this researcher worked on stellar collisions? Stars didn't collide! All the models I had made governing their motions through my simulated galaxy assumed this was the case. If it turned out not to be ... if it turned out stars did regularly slam into each other ... if it turned out that ALL MY RESEARCH WAS WRONG ...!

The email continued by saying that they were going for dinner at a local Indian restaurant that evening. I cast aside my keyboard and told Evert I would be taking the chicken vindaloo.

In fact, I need not have been so worried. The ratio between the size of a star compared to the distance between them is normally so large that even when galaxies merge, the stars do not run into one another. The chance of a star like our Sun hitting another star is so remote that we would have to wait for the entire age of the Universe for it to occur.

There are, however, other places in our galaxy where the probability of two stars colliding is much higher. The first is in dense clusters of stars and the second is in the centre of our galaxy, close to the super-massive black hole. Over dinner, Fabio explained to me that it was the latter scenario that he was investigating; looking at a population of stars close enough to the central black hole that they could be strongly affected by the force of its gravity.

Despite the frightening images that a black hole conjures up, if you remain outside its event horizon there is no particular cause for alarm. Objects that drift past this point can never be seen again, but stars at a greater distance can orbit the super-massive black hole safely in the same way as the Earth goes around the Sun. Yet Fabio told me there is something very strange about a few of the stars very close to our galaxy's super-massive black hole; namely, that they are very young.

Stars form when clouds of gas become dense enough that they collapse under their own gravity. Once this has happened, the object produced is very hard to break apart, but during its formation the cloud can be more easily disrupted by an outside influence. Close to the super-massive black hole, clouds are not able to form stars before the black hole's gravity rips them to pieces. Stars that are found in this region are therefore usually older objects that were born further out in the galaxy and have been scattered in over time. How there could be young stars so close to the black hole was consequently a mystery, but one Fabio thinks he has found a solution to during his PhD work.

Fabio postulates that a known mechanism for breaking apart binary stars might sometimes go the opposite way, and cause two stars to merge. In a binary system, two stars are born so close together that they orbit about a common point between their centres. When such a pair approach the super-massive black hole, the black hole's gravity can disrupt the binary, resulting in one star orbiting the black hole and the other being ejected out of the galaxy at high velocity. In Fabio's models, a similar event occurs but instead a star being ejected, the black hole's influence makes the binary stars collide and merge to form a single object. This new composite star has the same chemical composition as the two old stars, but is now twice the mass. This makes it appear to observers to be much younger than it truly is, since more massive stars evolve faster than their lighter counterparts.



This movie shows the results of one of Fabio's simulations[*] of a binary merging due to the gravitational influence of a super-massive black hole. The black hole is not shown directly, but its effects can be seen upsetting the orbit of the two stars which get steadily closer and collide, before settling into a single object. [Click on the movie to play and if that sadly fails click here. If you weren't concentrating and want to start the movie from the beginning but 'reload' is treating you badly, try hitting 'shift' at the same time as 'reload'.]

This was an exciting look at one of the most dangerous areas of the galaxy. Nevertheless, from the point of view of the fate of the Earth, I was rather glad we were hanging out in a quieter suburb.

--
[*] Journal reference: Antonini, Lombardi & Merritt, 2010, astro-ph/1008.5369 .

Answering the ultimate question

"That computer learnt word associations from Wikipedia. So it knows that 'opus' goes most commonly with 'Rome', 'sushi' with 'fish' .... and therefore 'robot' with 'violent genocide of the human race'?"

We were discussing the latest colloquium from the Origin's Institute which this week had been given by Geoffrey Hinton, a specialist (and indeed founder) on neural networks from the University of Toronto. Apparently, we had inadvertently stumbled across the cause of the downfall of humanity; that the tool used to teach computers about language also happens to include a scene-by-scene description of the 'Terminator' series.

An artificial neural network is like an electronic brain; it is a computer program that is designed to work in a similar way to biological neurons. Like the brain (and unlike most other types of computer programs), neural networks can 'learn' to do a particular task by being given many examples. They are used in pattern recognition (e.g. reading a person's handwriting) and for finding complex relationships (e.g. stock market predictions or medical phenomena, where the outcome is the result of many combining factors). 

In his talk, Professor Hinton took us through one of the early algorithms for teaching a neural network. In this technique, the computer is given data --for instance an image of a hand-written number-- that it must identify. It looks for specific features in the pixels, such as the presence and position of curves or straight lines, and then makes a guess. The guess is then compared with the correct answer and the relative importance of the different features being detected is adjusted to improve the algorithm. For example, a double loop would be very important since it identifies an '8', whereas a single loop is less significant since it could belong to a '0', '6', '9' or even squiggly drawn '4'. After this training, the computer program can be used to identify a wide range of hand-written numbers accurately.

This method works, but it has its drawbacks. Having a large number of fixed features that must be programmed for the code to identify makes the process slow, inflexible and results in poor scaling. Additionally, the fact it requires labels (e.g. 'number 1', 'number 2') to apply to the data differs from the way our brain works. Each image that our brain processes can rarely be categorised by a single label. For instance, a cow in a field has a colour, a position and key tell-tale signs that indicate it might actually be a man-eating Minotaur -- all of which are not encompassed in the label 'cow'. 

An improvement to this was to replace the pre-defined features that were given to the computer to identify an object with a set of criteria it created itself based on experience. This meant the computer no longer needed to know anything about the data it was being given. It could be a series of drawings of the number 2, pictures of houses or Minotaurs disguised as cows, and the algorithm would find common collection of characteristics that it could use to identify them. An example of such an identified feature for a '2' would be a wedge of light coloured pixels in the top left corner of the image, followed by a diagonal dark line -- the start of the 2's top arch.

Left to do this, the features identified by the neural network fell into two main categories; a small set of coarse criteria based on colour and a much larger set of finely tuned criteria based on shade. An example of both these types of characteristics would be a person standing against a wall. The sharp line between the white of the wall and the darkness of their hair would form a colour-based feature. Their facial features, meanwhile, would be picked out in a multitude of different shades in the same 'skin' colour. Interestingly, the resultant map of these computer-identified features closely resembles that of a monkey's brain.

Algorithmically, the set of data defining characteristics is honed by the computer program calculating first a set of features, then set of features of the features.... then a set of features of the features of the features. This leaves a collection of basic patterns that can be used to accurately identify the type of object for which the network has been trained.

An interesting question Professor Hinton than proposed was could such a neural network use its pattern recognition to predict the next stage of a sequence, rather than just identify objects? In particular, could a program predict the next word in a sentence?

To tackle this problem, the philosophical sounding question 'what is a word?' had to be answered. It turned out to be easiest to consider a word simply as a sequence of characters and to train the neural network to predict the 11th character in the string fed to it. This process could be continually repeated to build up entire sentences.

To teach the network about how words are formed, PhD student Ilya Sutskever gave the computer 5 million strings of 100 characters each from wikipedia. At the end of this training, the computer was told to build entire paragraphs of text to assess what it knew. It turned out to almost always produced real words. In the few occasions where it made some up, they sounded like they ought to exist. For example, 'ephemerable' or 'interdistinguished'. It was also good at semantic associations. It knew that many words that started 'sn' were connected with the upper lip and nose, e.g. 'sneeze', 'snarl' and, uh, 'snow' when used as a synonym for an illegal drug. (A fact noted by the speaker, not the author of this blog). Likewise, it knew that sentences containing 'opus' often also contained 'Rome' and that ones mentioning 'Plato' frequently went on to say 'Wittgenstein'. Similarly to the human brain, however, it often did not know why these connections existed. This produced sentences that made sense grammatically, but would not actually be found. For example, it talked about the "several Irish intelligence agencies in the Mediterranean' which is geographically unlikely.

A fact I found most surprising from this work was the length of information the computer program drew from. When deciding what the next character should be, it did not just look at the few before it, but at the long pattern of characters (that is, entire words) that preceded it. This allowed it to almost always use a consistent tense and to close parenthesise.

The knowledge could be applied to words it had never seen before. Upon being given two uses of the fictitious verb 'to thrunge', it guessed that the next character in 'Shelia thrunge' would be an 's' whereas the one following 'people thrunge' would be a space.

At the end of the day though, all Douglas Adams fans will agree that there really is only one question of any importance for a neural network trained on language. The computer was therefore asked to complete the ultimate question:

'The meaning of life is ...'

To which it replied:

 '.... literacy recognition.'

Clearly, it had been listening to students and postdocs panic about their paper count in the laboratory.

So are we close to really understanding how the human brain works? Professor Hinton took the opinion:

"It's a device with a few trillion parameters ..... how hard can it be?"

The littlest astrophysicist

While many a Disney princess had gifts bestowed on her at birth by magical fairy godmothers, the graduate student community offered their own type of benefaction to our newest department member, postdoc Evert's baby son, Arthur.

"If we all start speaking in Klingon, then the baby will become fluent!"

"How many actually speak...?" I cut-off my own question, deciding I didn't wish to know the answer.

Fortunately for Arthur, the languages he is most likely to first adopt are English and Dutch, since his parents are both from The Netherlands. (After which, a bazillion more will be added; because the Dutch roll like that.) Unlike his parents however, Arthur is also a Canadian, by virtue of him being born in the hospital here in Hamilton. As I counted the fingers of the tiny boy, I wondered if an equivalent term to 'army brat' should be created for children who seemingly have a random extra nationality, unconnected to any in their family. Perhaps 'postdoc spawn'. It could catch on!

In celebration of their son's birth, Evert and Tine brought in a traditional Dutch treat for the arrival of a newborn, "beschuit met muisjes" or "biscuits with little mice". This tradition stretches back to the 17th century and consists of a rusk-like biscuit sprinkled with sugar coated anise seeds. Blue and white seeds are used to celebrate the birth of a boy and pink and white are used for a girl. The name 'mice' comes from the little stem on the anise seed that resembles a tail.

Naturally, the birth of a baby results in many challenges for all concerned. For me, it was working out what the hand-made card announcing Arthur's birth said, since it was all written in Dutch. For Evert, new techniques that simultaneously supported stellar evolution investigations and baby evolution support needed to be developed. The currently favoured method is a one-handed devotion to each task. It could be that while Arthur's first spoken language is Dutch, his first written one is going to be FORTRAN.

[While no comment is made in the text, the reader is left to determine the gender-related split between primary interest in baby / food that the above photos suggest.]

When I was your age, Pluto was a planet

“A girl came up and told us that her teacher had said there were nine planets in the Solar System but she had tried to tell her that she was wrong, since Pluto wasn’t a planet, it was a dwarf planet!”

I looked up from browsing the photos that Rachel Ward, a Master’s student working on modelling the early stages of star formation, had taken at the Ontario Science Centre’s ‘One World, One Sky’ event in the middle of October. “How old was she?”

“Five.”

Huh. I was pleased to learn that someone was keeping up with the astronomical publications, even if it was not always me.

The event this had occurred at, and the pictures from which I was now perusing, had been an outreach initiative by Toronto’s astronomical community. It built on the success of the ‘International Year of Astronomy’, a year-long celebration in 2009 to mark the 400th anniversary of Galileo Galilei’s use of the first telescope. Throughout that year, institutes around the world had made a particular effort to hold public seminars, observing nights and (in the case of Japan) to create an astronomically-informative toilet roll. (For the curious, yes, I do have one. I refuse to comment on whether I have used it, although I will say that the first sheet is dedicated to the topic of my research).

The international nature of astronomy was the continuing focus for the ‘One World, One Sky’ event, which included talks about the role of astronomy throughout history as well as in society today. The ancient Egyptians, for instance, were very familiar with the night sky and used their knowledge to predict the annual flooding of the Nile, an essential part of their agricultural cycle. They recognised that the flood occurred when the dog star, Sirius, rose just before the sun, an event that took place each summer in late June. 5,000 years later, we see the heliacal rising of Sirius in early August due to our change in position as we move through the galaxy.

Modern day agricultural issues were later blamed on astronomy when the subject of crop circles arose during a panel discussion for ‘Ask an Astronomer’. Rachel, with fellow graduate students Aaron and Mikhail, took on the barrage of question from the public that ranged through profound (“What is space?”), taxing (“What is dark matter?”) and into the fictional (“What about UFOs?”). For the rurally curious, incidentally, the origin of crop circles is more likely to sit with the alcohol-fuelled back row of students than with an out-of-space phenomenon.

Rachel’s small solar system expert approached her while she was manning one of the booths demonstrating various astronomy based concepts. Included in this section of the day was the opportunity to build a comet out of frozen ice, carbon dioxide, dirt and (more surprisingly) windex, which was apparently used as a source of ammonia. There was also a race to build a space station, a meteorite collection and displays on the astronauts from around the world.

After hearing about all this, I realised I had to get back to work. There was at least one five year old eagerly waiting for my results.


[Photo caption from left to right: (1) Aaron answers a question during the 'Ask an Astronomer' panel discussion (2) Rachel demonstrates how to build a comet (3) Mikhail shows features on the surface of Venus to astronomers-in-training.]

Questioning the standard

Around 13.7 billion years ago, a hot, dense and infinitesimally small point started to expand rapidly in an event known as the 'Big Bang'. As it inflated, the matter within it cooled, condensing into galaxies and stars until it became the Universe we see today.

Ironically, the man who coined the term 'Big Bang' was not one of the founders of the theory, but one of its opponents. Sir Fred Hoyle was an astrophysicist at the Institute of Astronomy in Cambridge and is possibly better known for his naming of the theory he did not believe than for his ground breaking work on stellar nucleosynthesis; the mechanism by which stars form the heavy elements such as carbon and oxygen. Hoyle favoured a 'Steady State' cosmological model, whereby matter is continuously created as the Universe expands, so there is no absolute beginning. In 1949, he used the term 'Big Bang' (some claim derisively) while discussing his research on the radio, and the striking image this conjoured caused the name to stick for both its supporters and opponents alike. Since then, the Big Bang theory has become accepted as part of the standard model for cosmology and very little is heard of alternative theories outside historical reviews of the field.

For me, the first time I head anyone talk on a different model was this semester when Professor Jayant Narlikar was invited to speak at McMaster, giving talks both at the Origins Institute and in the Astronomy department. Professor Narlikar worked with Fred Hoyle while he was at Cambridge in the 1960s and, like his mentor, is a proponent of steady state theories. His affiliation with Hoyle and subsequent astrophysical career would have made him a speaker not to be missed, but I was also intrigued and (I admit) skeptical. Few people nowadays questioned the Big Bang theory, so was it not time for Hoyle's old team to drop their searches for an alternative explanation?

With this in mind, I listened as Professor Narlikar began his talk by explaining what had driven himself and his colleagues to seek out a new cosmological model. He explained that in 1948, the Armenian scientist, Viktor Ambartsumian, raised ideas about astronomical objects known active galactic nuclei (AGN). These highly compact regions were seen to be pumping energy into space, suggesting that they were violating two of the sacred rules in physics; the conservation of energy and momentum.

To explain these systems, Narlikar, Hoyle and a third astrophysicist, Geoffrey Burbidge, developed a variation on Hoyle's original Steady State theory which become known as the 'Quasi-steady State’ theory in 1993. Like the standard picture, Narlikar's universe contains dark energy that permeates all of space. In the Big Bang theory, however, the presence of dark energy causes the Universe to expand, whereas here it has the opposite effect, pulling the Universe in on itself. To off-set this, Narlikar introduces a second energy type called the "C-field". When the C-field energy gets very high, it creates both matter and space via Einstein's equation for the equivalence of matter and energy, E = mc², thereby continuing to conserve energy.

The C-field's strength increases around very compact, massive objects (such as AGN), causing a mass production of particles such as what Ambartsumian described. The standard picture of AGN is that they are black holes that are accreting mass that radiates furiously as it is accelerates. In Narlikar's model, black holes do not exist in the traditional sense, but are places where the C-field is exceptionally strong, producing explosive creation events of matter and space.

The resultant creation of space dilutes the C-field, eventually causing it to become much weaker than the dark energy which takes over and starts to pull the Universe back in. As space collapses, the C-field density rises until it once again dominates the dark energy and forces the Universe to perform another change of direction. It is a giant heart beat, lasting billions of years.

So can this be tested? Professor Narlikar's idea was straight forward; while most of the galaxies and stars would be destroyed as the Universe contracts, a few would survive into the next heart beat. Therefore, if we could find stars older than the Big Bang model gives for the age of the Universe (that is 13.7 billion years), it is possible that they came from a previous expansion phase in a universe that is better fitted by Narlikar's model.

Professor Narlikar's team conjectured that such surviving stars were likely to be ejected away from our galaxy during the turmoil caused in the contraction and expansion of the Universe. They therefore searched for old stars near one of our Milky Way's satellite galaxies, the Large Magellanic Cloud. Examining data from the Hubble Space Telescope, the astronomers found a number of candidates that appeared to be abnormally old. However, Narlikar's group were cautious; could there be alternative theories as to why these stars might appear much older than they really were? For instance, if the star was really not a single object, but two stars orbiting one another closely in a binary, it would be redder (and therefore seem older) than either twin actually was. Alternatively, their candidate might be not very old, but very young, too young to be accurately dated by the techniques they were employing. Finally, they might have made incorrect assumptions about the composition of the star, causing the age estimates to be off.

After considering all these points, Professor Narlikar concluded that, while they had possibilities for stars whose age exceeded 13.7 billion years, it was impossible to prove conclusively at this time.

I continued to think about Jayant Narlikar's talk for the rest of that day. It stayed in my mind not because he had convinced me that the Big Bang theory was wrong, or even because the talk had been well presented and interesting (although it had been). It was because it reminded me strongly why I became a scientist; to question all and every idea in the search for the truth.

In the 17th century, Galileo Galilei was condemned for his support of the Copernican model of the Solar System which placed the Sun, not the Earth, at its centre. (Amusingly, the Catholic Church only publicly vindicated him in 1992). This history is evidence for how easy it is to become complacent with established theories and loose track of what science is about. After listening to Professor Narlikar's talk, the direction my own research could go in seemed to double and triple before my eyes. I remembered that I should not be be confined by what people had done before, but rather use the ideas as stepping stones to go in any number of directions.

Thanksgiving

Canadians have many strange and bizarre habits. They buy milk in bags, describe a six inch snowfall as 'light' and have a chain of automotive stores that are also the place to go to for alarm clocks and space heaters. Then in the second week of October, they have a holiday devoted entirely to food.

Unlike the USA counterpart which remembers the arrival of the pilgrims in the New World, the Canadian Thanksgiving celebrates the harvest. I should mention I discovered this historical fact through google, since raising the topic at the lunch table merely produced a discussion surrounding plans for family visits and huge quantities of food. In common with their near neighbours, Canadians often travel to visit kin for the long weekend which meant many people were due to be out of town.

The exact count of absentees, however, was smaller than might be suspected due to the number of department members from other countries. The postdoctoral community in particular is very international, with five out of the seven postdocs in Physics & Astronomy coming from outside North America. This phenomenon is not limited to McMaster; while I was at the University of Florida, there was a standard joke that only one postdoc at a time was allowed to be an American.

Postdoctoral positions are short, normally between 1 and 3 years, and are designed to give young researchers experience by working with senior members of their field. Due to the nature of the job (skilled and fixed term), visas are relatively easy, if sometimes tedious, to acquire and therefore many people take the opportunity to work in another country. This is especially true in Astronomy, where the scientific instruments are incredibly expensive and the number of professionals in the field is relatively small (the International Astronomical Union has around 10,000 members). This results in strong collaborations between countries being an essential requirement of the work. Parts of Europe go as far as to expressly discourage their own nationals for applying to postdoctoral positions in their country, desiring them to gain experience abroad. This multicultural mix feeds through to the faculty level professors who, while all now settled in Canada, have their roots from all over the world.

From a personal perspective, this is something I enjoy most about being an Astronomer. Since graduating from my doctorate in 2005, I have worked in New York, Florida, Australia and Japan before starting my post here in Canada last November. The chance to experience life in a different country is truly amazing and something I have wanted to do since being a small child. Of course, there are downsides. Permanent faculty jobs are sparse and highly competitive and potentially moving countries every few years with a partner or family while you try and secure a position can take its toll. I have had several friends who left the field entirely for just this reason.

My immediate problem though, was not the country for my next job but the location for my dinner. It seemed to me that eating a modest meal on my own at Thanksgiving was clearly not embracing the culture. Fortunately, rescue was at hand in the form of Ben Jackel, a graduate student working on the creation of magnetic fields in disks around massive objects with Professor Ethan Vishniac. Ben volunteered his apartment for a Thanksgiving dinner, complete with a large ham. I joined Ben, his wife Margaret and two other graduate students, Tara and Leo, to more food than I could fit on a plate in one go.

Moving was more challenging than galaxy formation for the next 24 hours. I was told this was normal.

The moon illusion

"So why do you think the moon looks larger on the horizon?"

The question was posed by Rob Cockcroft, a graduate student who was also a presenter at the University's McCallion Planetarium. He was about to present a show dedicated to the moon and thought it possible he would be asked this question by one of the audience.

I blinked and looked up from my sandwich. "It does?"

I realized immediately I had just failed as an Astronomer. Yet the truth of the matter was that if an astronomical object appeared too large in my simulations, I had probably messed up the units in my calculation and caused the Universe to expand too slowly. Actual objects were not really my thing.

Fortunately the rest of the lunch table were more use.

"Isn't it because the moon is closer to other objects, such as trees, when it is low in the sky?" another graduate student asked. "Compared to those the moon will appear bigger."

This was a logical guess and one Rob himself had held until he had looked into the matter. The effect is known as the Ponzo Illusion and it is an optical effect that causes the human mind to judge the size of objects based on their background. Simple diagrams such as the ones shown here easily demonstrate this effect exists, but it is not the cause for the moon illusion, which has been proven to occur even on a featureless plain such as the ocean.

Another popular myth is the moon illusion is caused by the distortion of light in the Earth's air. It is true that as the moon sinks towards the horizon, you view it through a thicker layer of atmosphere, but the bending of light this produces actually causes the moon to appear smaller, not bigger.

In fact, Rob's investigations turned up no definite reason for the moon to appear larger; it seems no one knows for sure. The most common explanation, however, is that our brains have a view of the sky that is not a perfect hemisphere (like a planetarium) but a squished, shallower arc, more like a soup bowl. This causes us to believe that an object on the horizon is further away from us than when it was directly overhead. Since the moon's size actually hasn't changed, our brains assume that is must be larger at the horizon since it is apparently at a greater distance.

Quite why our brains would do this is a mystery. One argument suggests that we have evolved to be better at judging the size and proportion of objects that are close to us, since we are far more likely to be eaten by them than something at the bottom of a cliff or high in the sky. No one though, is entirely sure and some people reportedly don't experience the moon illusion at all. For those super interested, a good description of the moon illusion, including the flaw in the soup-bowl sky theory can be read here.

As I finished my lunch, I wondered if I was one of those rare people unaffected by the moon illusion. That would turn my folly at not knowing about it into the product of superior perception, not incompetence. It was a long shot, but I made a mental note to check next time there was a full moon.