Astronomical Concepts – Week 7

This week – special relativity.


We started with the two main axioms of special relativity:

  1. The laws of physics are the same in all inertial frames of reference

  2. The speed of light is constant (299,792,458 m/s)

Tonight we had to imagine we were floating through space in a spaceship. Are we stationary or are we moving? Are the stars stationary or are they moving? Relative to us of course. With the window blinds down on our spacecraft we have no way of knowing if we are moving or not, there is no experiment we can do to find out.

However, an observer on another spacecraft has a different point of view. On our spacecraft if we bounce a ball we see it go down and then up in a straight line. If an observer on another spacecraft could see us bounce a ball as we drift past them in our spacecraft, and they are stationary they get a different point of view of the ball.


The definition of ‘now’

We accept that certain events that happen can be simultaneous. But how can we determine that two events that happen in different locations are simultaneous?

On Earth we carry clocks and they are synchronised, we accept that two events that happen happened at the same time. What we have to accept is that clocks, time, is influenced by motion. Einstein realised that space contracts and time dilates through motion. A moving clock runs more slowly as its velocity increases, until, at the speed of it stops running all together. So having clocks that run at different rates leads to strange effects – simultaneity is relative. Whether or not two events are simultaneous depend on your frame of reference.


So, one person’s definition of time is not the same as another’s. Also, the faster you travel the slower you age. At speeds close to c the effects are huge, at smaller speeds less so.

Further, the faster you move the more you contract. Close to c the amount of contraction is great, at slower speeds less so, tiny amounts. An observer at rest relative to the moving object would observe the moving object to be shorter in length of motion. As the object increases in speed and gets close to c the object would appear much shorter.


Special relativity is a work of pure genius by Albert Einstein. Our session tonight was an introduction, a mere taster of the theory and we were only able to scratch the surface. I loved the session, the concepts are so interesting, if a little hard to get your head around. Much more information about special relativity can be found here.

So, the only true constant is the speed of light. The faster you travel the more time slows down for you and the more you contract.

With the invention of atomic clocks we can now measure time to billionths of a second and can be accurate to within one second over 3.7 billion years. Einstein said that realising gravity and acceleration were the same thing was “the happiest thought of my life”.

Astronomical Concepts – Week 4

This week’s main topic was light.

James Maxwell

James Maxwell was a Scottish scientist who lived from 1831 to 1879. He is well known for the research he did on electromagnetism and light, building on the work of Michael Faraday. He produced a set of equations that explain the properties of magnetic and electric fields which helped to show that light was an electromagnetic wave. He was able to bring together well established laws of electricity and magnetism and with Faraday’s law they could imply that any disturbance in the electric and magnetic fields will travel out together in space at the speed of light.

He also described Saturn’s rings as numerous small particles, and this theory was proved later on in the 20th century by a space probe.

Einstein’s Photoelectric experiment

Einstein’s experiment showed that packets of light, called photons, contained a fixed amount of energy that depends on the light’s frequency. When a metal plate is exposed to light electrons are expelled. This is the photoelectric effect. The effect was discovered by German scientist Heinrich Hertz in 1887. His observations showed there was an interaction between light and matter. But Albert Einstein was needed to explain the theory further in 1905, his theory of light. Einstein said that light is a particle, called a photon. Einstein was awarded the Nobel Prize in physics in 1921 for his experiment.


Spectroscopy is a technique used to measure the light that is emitted or absorbed or scattered by materials. It breaks light into its component parts and this information can be used to identify and quantify those materials.


When light is absorbed or reflected by materials not all light behaves the same way. Only certain wavelengths of light are absorbed other get reflected. When you seperate the light that is passing through a sample you end up with an emission spectrum or absorption line.

An emission spectrum in the visible light range may look like this.


A spectrum like this would be created when material is given extra energy and that extra energy is later emitted as light energy.

An absorption spectrum would look like this.


A spectrum like this is created when light is passed through a gas or liquid or strikes a solid. Certain wavelengths of light will be absorbed by the material and later emitted in random directions. Most wavelengths will pass through the material without being absorbed. sun_spectrum

The image above shows a spectrum of our sun. From this spectra astronomers can tell what elements the sun is made from, for example hydrogen and helium. It is like a rainbow with holes, the holes are coming from the absorption of energy at a particular wavelength, at a particular colour, by the atoms in the cloud. This goes back to the energy levels of the atom, of only taking energy at very particular energies, as electrons move from one excited state to another excited state. So what you’re seeing is the absorption of photons by atoms. When energy is absorbed you are seeing the energy raising the energy level of an electron. So, we see the rainbow because the inside of the sun is hot and it emits a continuous thermal spectrum. The atoms in the outer layer of the sun absorb some of the energy and use it to promote electrons from a low energy level to a high energy level.


Astronomers also take pictures of light, usually through a filter. Astronomers want to see what the light looks like in red light or green light.

Astronomers also do timing with light, which means to measure the brightness or phase changes as things happen in time.

The combination of spectroscopy, imaging and timing can tell us all kinds of information from the thing we are looking at. We can tell hoe fast something is rotating, if it is moving towards or away from us, temperature, density and composition. Light is our spaceship, we can’t travel to stars and planets light years away but light does travel to us, it is the only way to get the information we need.

Doppler effect

Light waves from a moving source experience either a red shift or a blue shift in the lights frequency. A light source moving away from a stationary observer causes a shift towards the red end of the light spectrum, called a red shift. When the light source moves towards an observer the frequency shifts towards the blue end of the spectrum.


Why is the sky blue?

The sky is blue because atoms in our atmosphere scatter blue light more than they scatter red light. When we look towards the sun at sunset we see red and orange because the blue light has been scattered away from the line of sight. Blue is scattered more because it travels as small and short waves.

That’s enough about light, next week is all about the sun.

Year 5, MARS & STEM in Term 1

What an awesome term of STEM we had in year 5! The main objectives were to learn about the planet Mars, space missions to Mars, the role of NASA and the Jet Propulsion Laboratory and the people that work there, discover if humans could live on Mars and what life would be like there.

So, lots of talk about lots of my favourite things: space, Mars, NASA/JPL, Adam Steltzner, The Martian, amazing technology, science and engineering, really inspiring stuff.


As well as the main learning objectives I had planned at the start of the course, some extra opportunities arose to fit into the busy schedule to enhance the course further. March 14 was Pi Day and I planned a special lesson with help from a great resource I found from the NASA website called Planet Pi. I adapted the lesson slightly for year 5 and they coped with some new and tough maths admirably. This lesson highlighted how NASA scientists use Maths in their jobs to learn about planets and other celestial bodies. I explained the maths and formulae clearly and used some great visuals to help the girls understand the maths and why it was needed. I loved the example of using Pi to explore a planet, this was such a great lesson!


Another great lesson we had this term, and which was a complete and unexpected surprise was the Skype with Andrea Boyd, an engineer with the European Space Agency. Andrea lives in Germany and was good enough to stay up late at night to speak to all of year 5 at 9am Sydney time. Andrea spoke about her education and career in the space industry, which was very interesting and inspiring for our young girls. Our students prepared some great questions to ask Andrea about space, the International Space Station, astronauts and more. Our girls did a great job, were beautifully behaved, very polite and engaged with this brilliant, young, Australian woman. We learnt so much about space and how astronauts live and work on the ISS. This was a really exciting lesson which everyone enjoyed! Big thanks go to Jackie Slaviero, founder of One Giant Leap Australia, for putting me in contact with Andrea and then for sending me an amazing pack of goodies from NASA.


The students seemed to love our STEM lessons this term. Space is such an interesting, exciting and inspiring topic for young and old, and I was so pleased with how they engaged. I love the questions they ask, they are so curious and what to learn everything. As well as learning about Mars we learnt about black holes, the Earth and Moon, the ISS, the speed of light, galaxies and more. We could quite easily study space for the whole year, and I gladly would.

Next term… students continue their STEM journey to Mars when they work in engineering groups to design and build their own Mars rover, based on the Mars Science Laboratory (MSL), aka Curiosity. Curiosity has been a common theme throughout the term and I talked a lot about it when I talked about JPL engineer and EDL team leader for Curiosity, Adam Steltzner, a really inspiring speaker.


His TED talk ‘How Curiosity changed my life, and I changed Hers’ is one of my favourites.

We also looked at rover facts and a great video called ‘7 minutes of terror’ which details how the rover made it from the top of the Mars atmosphere travelling at 30,000 mph to the surface travelling at a few mph in just 7 minutes. Another must-see video!

Like I said, I could teach this topic all year and not get bored! I used this video for an which included some questions about the EDL of Curiosity. A great resource for incorporating video into classes.

Students produced some wonderful work including ‘Selling Mars: selling land on Mars’ advertisements and a ‘NASA profile’ of an inspiring NASA scientist they found from the website We Are The Martians.

So next term… engineering groups, specific roles for each girl in the group, designing and making a Mars rover, making wheels and incorporating LittleBits electronics to make the rover move, engineering guide with project milestones, evaluations, presentations, creativity, teamwork and fun!

Let’s hope ours will look better than this one!