Cut yourself open!

Tonight after school, I sliced open Gabe.

Actually, we made fake wounds. We made fake flesh by mixing flour and water into a dough, and mixing it with coffee for skin tone. I attached it to his arm using Vaseline, smearing the edges down with more Vaseline so that it was a swollen lump on his arm.

I then ran a bread knife through the middle, gashing it open like a large wound.

We made blood using chocolate sauce (the Paris Hilton of chocolate sauces: thick and rich) mixed with red food dye.

I dribbled it down through his fake wound, letting gravity drag droplets naturally down his arm.

All the while we talked about types of blood (venous and arterial) and other things that lie beneath the skin.

And the results:

Oh, the agony!
Oh! The agony!

It really hurts dada!It really hurts, dada!

Actually, it tastes like chocolate…

I give this after-school activity two thumbs up!
Two thumbs up!

A little Penn and Teller

I had a number of influences for An Evening of Rough Science.  One of the most important was stage magic.

I have a larger and more detailed talk about how science demonstrations and magic tricks have a lot in common.  That’s a subject for another time.

Right now, here are a couple of clips of Penn and Teller that have influenced me over the past two years.

How slight of hand tricks can influence science demonstrations came to me while reading Derren Brown, but Penn and Teller have a brilliant act that lays out the (so called) rules of slight of hand.

Penn and Teller are also famous for telling people how their magic is done, and the cup and balls act with clear cups is one of their most famous. Interesting that in actually seeing how it is done in no way removes anything from the experience. (Interesting, too, how in this video the acoustics of the tomb they are in are so terrible, Penn has to really crank down his usual exuberance.)

Penn now explains human perception of numbers. No magic, but a great way to make an otherwise dry subject engaging.

Larger scale now.

An Evening of Rough Science

I am putting on a show!

Rough Science brochure

In an Evening of Rough Science we will conduct an autopsy on a microwave, unweave the rainbow to make the sky is blue, and unravel the challenges of how to explain Climate Change to your dad.

Join Sean Elliott, a science communicator with over ten years experience of writing and presenting shows for Museum Victoria and the CSIRO, for an evening of Rough Science.

Wednesday, 17 August 2011.

For more info, and how to book, visit An Evening of Rough Science page at Theoretikos.

Bookings are essential!

Why is the sky blue?

It’s the quintessential question asked by toddlers, and I love the answer.

To get to the answer we need to lay down some foundation.

Number 1: the white light coming from the Sun is made up of all colours. Isaac Newton made a complete study of this, going so far as to identify seven individual colours in the spectrum created by light passing through a prism: red, orange, yellow, green, blue, indigo, violet. Truth be told, the colour indigo didn’t exist before Newton. He made it up as a colour between blue and violet because, among other reasons, seven colours was theologically more pleasing than six.

Number 2: the Earth’s atmosphere is not one hundred percent gas. It also contains tiny particle of dust, particles from smoke, microscopic droplets of water and other liquids.

When light is passing through our atmosphere, the parts of the light spectrum at the blue end are more likely to encounter a teeny particle and be deflected off-course. Light from the other parts of the spectrum are more likely to pass through unimpeded.

You observe this effect when the Sun is close to the horizon. The light from the Sun has had to pass through a large amount of the Earth’s atmosphere, so contains very little blue light and is mainly made up of oranges, reds, and yellows; the colours of sunset.

The blue parts get seen by people on Earth where the Sun is higher in the sky. This light is raining down on them from all directions, so it is as if the whole sky is glowing blue.

The effect is called ‘scattering’, and was first studied by John William Strutt, the 3rd Baron Rayleigh, otherwise known as Lord Rayleigh.

You can create the effect yourself by using a glass of water, a strong torch, and some milk. (I prefer using coffee whitener, but milk will do.)

In a dark room, shine the torch through the glass of water so that the beam is pointed to a white surface. Put in a drop of milk (or few grains of whitener). Less is more with this demonstration, so only at the very slightest amount milk. Mix the water and look carefully at the light glowing from the glass, and the light hitting the wall.

The milk (and the whitener) does not dissolve in water. Instead very small particles become suspended in the water. As you add more particles, then more of the colour spectrum has a chance of being deflected off-course.

As you add more milk, the glass should take on a blue-ish hue, while the beam on the wall will gradually become darker while cycling through oranges to reds. Eventually, there are so many particles in the water that every part of the spectrum is likely to be deflected, and the glass will be glowing white while the beam no longer appears on the wall.


This Rough Science was initially suggested by @sorrel_smith and her daughter. But how appropriate is the answer for someone under five?

No answer lives in a vacuum. Knowledge is layered and knitted. So if your toddler says “why is the sky blue”, do you tell them about the visible light spectrum, wavelengths of light, and Reighliegh scattering?

I would prefer to avoid the following:

“It’s complicated.”

“It’s magic!”

“It’s paint. Dulux range, sky blue.”

Instead I would try to give them a near-truth.

“The light from the Sun makes the whole sky glow blue.”

But why blue?

“Because of Earth’s air. If it was different air, it could be a different colour.”

It’s breadcrumbs leading the way to the whole answer. Also, it helps to answer other questions.

“When the Sun goes down, the glow goes away, and we can see the stars.”

True knowledge often doesn’t fit into a sound-bite. If understanding could be made in just one sentence, there would be no need for homework.

Radiation Part 3: Just what are your referring to?

We are standing in front of our pellet of radioactive material, but how much radiation are we absorbing?

This is another area where the answer is “depends”, and is prone to get muddled by people, particularly journalists.

Our radioactive pellet has a certain amount of activity, which is the number of disentergrations per second.  Remember that the atom’s mass is disentergrating into radiation, which is being sprayed in all directions from the pellet.

As the radiation zooms away, the exposure is the measure of the amount of energy it is depositing into the material it is passing through.

The absorbed dose is the dose of energy absorbed by a specific object.  For instance, by a volume of air, your hand, or your whole body.

Then there is the absorbed dose equivalent.  Depending on the type of radiation (ie, x rays, gamma rays, alpha particles) it may be absorbed by the body differently.  This can be measured by a film badge dosimeter (badge that goes black as you get exposed to more radiation of a particular sort.)


Homework: tomorrow count the number of times that the media uses the word “radiation” in a report, then ask yourself to which of the above they may be referring it.

Radiation Part 2: The Radiation Spotter’s Guide

Radiation comes in a variety of flavours.

For the sake of simplicity, let’s focus on three that come from radioactive decay: alpha particles, beta particles, and gamma rays.

Imagine our pellet of radioactive material. As we looked at in Part 1, the atoms making up this material will lose a small amount of their mass as a bullet of radiation that shoots into the wide world . The type of radiation the pellet emits depends on the unstable material making up the pellet.

If our pellet of material is undergoing alpha decay, then its atoms will be losing its mass in the form of alpha particles. These are the underachievers of the radiation family (though have an insidious dark side that we’ll see later; a bit like Scar from the Lion King.) You are easily shielded from them by a sheet of paper. Actually, even thick air or ever your skin is enough to stop these particle pushovers.

Beta decay creates beta particles, which have a higher energy and higher speed, and can happily pass through you like fermented prunes. That said, beta particles will be stopped by a material with a sufficiently high density, such are a sheet of aluminium.

A material undergoing gamma decay is really nasty. Its mass decays into gamma rays that easily penetrates skin, aluminium sheeting, concrete, One Nation supporters, and will only be stopped by a material that is sufficiently dense; say, a chunk of lead.

As the observers of this pellet of radioactive material, we are concerned about which type of radiation is being emitted. All three have the potential of doing damage to the cells in our body, but if it is weak like alpha particles, then the chances of it travelling the distance to us let alone penetrating our body’s cells is small. Beta particles have a higher risk, but the radiation to beware of is gamma rays, smashing through your body like a very small but high-speed bullet.


Carrying on with our accident at our hypothetical nuclear powerplant, the next questions we and any Walkley-winning journalist should ask:

o If the plant is leaking radioactive material, what sort of radiation is it emitting?

Knowing what sort of radiation is being emitted, then we can make an estimate of how dangerous it is to be exposed to it. And this is the subject of Part 3.

Radiation Part 1: What is Radiation?

When the media pronounces the word “radiation,” it is spoken in a terrifying font, conjuring images of poisonous muck oozing out from a powerstation, a monsterous tenticular nightmare sprouting from polypous perversions that will crawl about the countryside, reaching deep into your living cells to do something really naughty.

But what is radiation?

To understand radiation, we need to make a distinction between two terms: “radiation” and “radioactive material”.

Radioactive material emits radiation; the radiation zooms away from it in (more or less) a straight line in all directions until it encounters something it can’t penetrate. Imagine the material being a lightbulb, and the radiation is the light it emits.

Radiation can be a highly energetic particle, and it can be a wave. Radiowaves are a form of radiation. So is light. Some radiation is harmless to us. Others can alter us and our environment.

Imagine a pellet of radioactive material is sitting on the ground in front of you. It might be glowing because it is emitting radiation (not necessarily green like it does in the movies).

Now zoom down to the atoms of the material. Choose any atom and watch it. At some point that atom will shoot off some of its mass as a unit of radiation. We can’t predict when this happens. (The fact that you’re looking at the atom waiting for it to happen makes the process even trickier, which is a story in itself, and involves cats in boxes.) Nevertheless, when it does happen, the atom that is left has less mass, and will have different properties: ergo, it is now a different material.

What happens to the mass the atom loses? It become a unit of radiation, and takes off into the world like a students on a gap-year until it bumps into something or eats something it regrets in Kuala Lumpur.

Zoom back out and look at the pellet on the ground. Over time, the pellet of radioactive material changes as its atoms lose mass. The pellet will eventually change (perhaps through a range of materials) into something that is stable and no longer emitting radiation. Remember, it is impossible to predict when an atom will change, so you can’t predict when the entire pellet is completely stable. It is much easier to accurately predict when a fraction of the pellet has changed, so the life of radioactive materials are measure in the time it take for half of the material to change. Hence, “half-life.”

Depending on the material, its half-life be a few seconds, or it could as much as millions of years, or anywhere in between.

Whether the radiation is dangerous or harmless to us depends on the unstable material. Types of radiation and its effect on humans is the subject of Part 2.


There are two questions that should arise in your head, and the heads of any journalists, when an accident happens at a nuclear facility:

o Is the facility emitting radiation?

o Is the facility leaking radioactive material?

Two important and different questions. If the answer to the first one is ‘yes’, then it is an issue if you are standing in the facility, but not if you are sitting in a city several hundred kilometres away, even if the prevailing winds are in your direction. Imagine the radiation like light coming from a lightbulb: is it going to be brightest up close or several hundred kilometres away?

If the answer to the second question is ‘yes’, then there is a different set of concerns and more questions to ask. Why type of radioactive material has leaked? What is the size of the material? If we stretch the light bulb analogy, imagine clouds of light bulbs, different sizes, drifting on the wind, settling over the countryside. All of these lightbulbs could be emitting light…

For now, if you are journalist about to start an article on Fukushima, ask yourself if the term you are looking is “radiation” or “radioactive material.” The distinction is important.

We don’t use the Richter Scale

Well, kind of, sort of, no.

It’s some common parlance to talk about earthquakes being “something point sometime on the Richter scale.”  But these days that is likely to be wrong.

The Richter Scale was invented by Charles Richter with the help of Beno Gutenberg in 1935.  Richter was looking for a way to quantify earthquakes; attributing a number to an earthquake which could tell you about the amount of seismic energy released by an earthquake.

Before an earthquake goes off, huge amounts of potential energy is built up in the earth’s crust: for instance, as two tectonic plates move against each other.  There comes a point when the crust can no longer hold the stress it is undergoing, and rocks crack and deform as the two plates give way.  This seismic energy radiates outwards as waves through the surrounding land, moving the ground beneath our feet.

(Experiment: Get two chocolate chip biscuits.  Pretend they are tectonic plates and push them against each other until explode in your hands.  Biscuit quake!  Don’t worry about the mess: if you sing like Carole King at the same time, people will forgive you.)

Richter’s scale was intended to measure this energy and report it as a single number, much the same way the “apparent magnitude” scale used in astronomy to measure the brightness of stars and other objects in the night sky.

However, the scale was developed using a particular instrument for measuring quakes:  the “Wood-Anderson torsion seismometer”, (future Rough Science article.)  The way the scale is calculated means that it is dependant on the instrument it was recorded on.  The value also become unreliable for earthquakes larger than 7.

These days the Richter Scale is only used for small, local earthquakes.  For earthquakes such as the recent Sendai earthquake, or the earthquake that triggered the 2004 Boxing Day tsunami, they are measure in the “Moment Magnitude” scale (MMS).  This scale also measures the size of earthquakes in terms of energy released, but is not dependant on the instrument it is measured on.

When you hear about earthquakes in the media, it is more likely they are measured on the MMS: for instance the Sendai earthquake was a magnitude 8.9 quake.  If someone tells you it was 8.9 “on the Richter scale”, tactfully correct them.

On the other hand, the MMS breaks down for small local quake, where the Richter Scale is still used.


I first started untangling the MMS from the Richter Scale when the 2004 Boxing Day tsunami happened.

There were some news articles saying it was 9.1 on the Richter Scale.  But then other articles mentioned this “Magnitude Moment Scale” thingy.

I was writing an information sheet about the earthquake and tsunami for the venue I was working at, and decided to investigate these two scales.  Wikipedia was still in its infancy, and the page on MMS was next the useless, having just a handful of equations.

So I called the geology department at a major university.  I ended up speaking to a lecturer, who kindly told me he was a bit under the pump at the moment, and that if I leave an email he’ll put me in touch with one of his postgraduate students.

The postgraduate student was prompt in replying.  That afternoon I got an email from him, which contained a single link to the Wikipedia page on MMS.

This Rough Science article is dedicated to that postgrad student, where ever he may be.

(Guest art by Gabriel Elliott, a drawing of a boat in a tsunami after watching a video of a Japanese town being destroyed in less than six minutes.)

Saturn’s Ears

A little over four hundred years ago, in the Grand Duchy of Tuscany in Italy, a man named Galileo Galilei was given a new toy that had become popular in the Netherlands. It was a wooden tube with some ground-glass lenses at either end, and had the cool property of seeing things far away as if they were nearby.

Galileo started pointing it at all sorts of things. What made him different from the casual observer was that he meticulously documented and repeated his observations, then published his results for anyone else to read and make their own observations.

(At the time you would have called him a “Natural Philosopher” as the word “Scientist” wasn’t coined until the nineteenth century.)

You have to remember that the generally accepted view of the cosmos for people living around him was that the Sun and all the planets went around the Earth. Not only was this common sense, but it was also what Aristotle (who lived two thousand years before) had said. And Aristotle was, you know, a genius.

The observations made by Galileo were new. The planets and the Moon appeared to be spheres.  Venus went through phases much like the Moon.  Jupiter appeared to have smaller planets going around it. And then Saturn…

Saturn was just weird.

Imagine you are looking through Galileo’s wooden tube with glass accessories pointed at Saturn. The hand ground-lenses magnify the image, but they’re not perfect. You’re looking through Earth’s atmosphere, distorting the light from Saturn through layers of air expanding and contracting as it heats and cools. Every servant footfall nearby rattles the image, until Galileo tells them to leave the wine jug and bugger off.

And what do you see?

It appears to be a shimmering circle. Out of either side are…what?

Seeing objects around Jupiter was big surprise. But what to make of these projections from Saturn. Mountains? Small planets very close to Saturn’s surface?

These handle-like projections had Galileo stumped. In a letter to his favourite pupil, Benedetto Castelli, he wrote “…the ball in the middle was seen quite distinctly and was surrounded by two dark spots positioned in the middle of the junctions of the mitres, or, that is to say, ears.”

Forty-five years after Galileo’s initial observations, another Natural Philosopher living in the Netherlands, Christiaan Huygens, using larger telescopes with more accurately ground lenses, identified the objects as rings around Saturn.


I first came across “Saturn’s Ears” many years ago in a funky show about the solar system. It was only a handful of lines, and went something like: “Galileo thought Saturn’s rings were ears! He should get his eyes checked!”

The line felt like a cheap shot. It invited the audience to think how smart they were to silly old Galileo. I suppose I was feeling the same feelings as Douglas Adams when he heard someone making a joke about indestructible black boxes, and how they should actually make planes out of the same stuff. A joke from ignorance.

It was a throw-away line, and jeered at Galileo’s work that, despite everything working against him, was still able change our view of the universe.

(Thanks to @annaryanpunch who found the Galileo quote, from

Why does the wind blow?

Pucker your lips and blow. That is air moving on a very small scale. Outside, wind is air moving on a very large scale. Great volumes of air!

How do you get a great volume of air to move?

Air makes up the atmosphere; the sphere that remains when you removed the Earth. It’s a thick shell of gas that goes right around the Earth, and extends from the ground up to the edge of space.

Because it’s made of air, it expands when it gets hot, contracts when it cools down. If a large volume of atmosphere is heated by the sun, it will swell. If air over the sea cools down, as it contracts there will be room for air nearby to move in. All of this air movement we feel as wind.


That’s a rough explanation. Atmosphere and weather is a very complex system. I haven’t mentioned the different layers of the atmosphere, and how the Earth’s rotation also effects air movements. But hopefully that’s enough for @sorrell_smith, who asked the question on behalf of her daughter.

One of the coolest experiments to see air expanding and contracting uses boiling water, cool water, a bottle and a balloon. (Usually at this point people say they’ve seen this one before, but I would wager your haven’t seen this version before.)

Fill the bottle to the rim with boiling water. Wait half a minute, and tip the boiling water out. Trap the now hot air inside the bottle by putting a balloon over the bottle’s neck. Now drop the balloon in the cool water.

As the air inside the bottle gets cold, it contracts. There’s now room inside the bottle for outside air to move in. But there’s a balloon in the way. The balloon, THUNK, gets pushed inside the bottle.

My question to you is: how do you get the balloon back out of the bottle?