Activity 1: Let's discover Infrared light
Using an infrared camera, you will show that there is electromagnetic radiation invisible to our eyes and that it is possible to build devices to observe it, just like SKAO will do.
An excellent demonstration of the existence of light that our eyes cannot see is based on an infrared camera and an ordinary black bin bag.
Ask students to put an arm inside the plastic bag and observe it. They will not be able to see the arm, as visible light cannot travel through the bag, which appears opaque to our eyes.
Then ask them to look at the plastic bag with an infrared camera. They will now see the arm inside the bag, thanks to the infrared waves that can pass through the bag, making it appear transparent on the camera.
Figure 4: Hands in a plastic bag, seen in visible light (left) and with an infrared camera (right). Credits: NASA/JPL-Caltech/R. Hurt (SSC)
After showing the existence of infrared light, explain to students that this is analogous to how SKAO's radio telescopes will create radio pictures of the Universe. Just like infrared radiation, radio waves are undetectable to the human eye, but they unveil hidden objects and phenomena in the Universe. Radio waves pass through clouds of gas and dust in space, whereas visible light is blocked, allowing astronomers to peer through these clouds and see the objects within or behind them (an impossible feat for an optical telescope, which observes visible light).
Activity 2: The existence of radio waves
You will use a RF (radio frequency) detector to pick up radio waves, just as the SKAO's telescopes will do to observe the Universe.
Radio waves can be an abstract concept, since they are undetectable by the human body. So, we will use an RF detector to detect radio waves.
First, demonstrate how the RF detector works. Bring the antenna close to a source of radio waves (e.g. an active mobile phone, a walkie-talkie, or a radio mic). The antenna will emit a sound or flash a light when it detects the waves. This demonstrates the existence of radio waves even if we cannot see them with our eyes.
After the demonstration, students could be given RF detectors and asked to explore the environment, in search of areas of high and/or low radio activity.
OPTIONAL: if you have a spectrum analyser, you can use it in a way similar to the RF detector. It picks up local radio waves and displays a real-time map of the radio frequencies in the 2.4 GHz band (frequencies of 2.4 GHz to 2.5 GHz). These frequencies are used for wireless communications, such as Wi-Fi networks, mobile phone signals and Bluetooth. Like the RF detector, this can be used to demonstrate the existence of radio waves, as well as the need to build the SKAO in remote locations, away from ‘radio loud’ areas. In fact, human activity generates a lot of ‘radio noise’ through wireless technology, which may cover the (much fainter) radio signals from space that the SKAO will look for.
Activity 3: Why do telescopes have a dish antenna?
Students will use a parabolic microphone to collect and amplify sound, understanding why radio telescopes have dish antennas (even if they DO NOT DETECT SOUND BUT RADIO WAVES!)
Ask students to use the microphone to hear someone speaking quietly on the other side of a room. They will be able to hear the sound through a set of headphones.
Then examine the microphone and explain to them that the shape of the bowl focuses sound waves to the microphone in the centre. This amplifies the sound, allowing the listeners wearing the headphones to hear conversations from quite a distance away. The bowl has the shape of a paraboloid (a 3D parabola). This shape reflects the sound to a point, called the focal point. The focal point is where the microphone sits. This is analogous to the dishes of the SKAO mid-frequency instrument in South Africa, which collect and focus radio waves to a detector at the focal point.
IMPORTANT: Please note, after using this piece of equipment, some participants may be under the misconception that the SKAO detects sound, rather than radio waves (a form of electromagnetic radiation, similar to light). Please ensure that participants are aware that the demonstration in this activity is an analogy.
Health & Safety notice: When the headphones are being worn, the microphone should not be subjected to loud noises, e.g. someone shouting into it. This could cause pain and/or ear damage to the person wearing the headphones.
Activity 4: data transfer
You will use the morse code to explain how telescopes transfer data with optical fibre technology.
Light can be transmitted over large distances and very quickly (at a speed of about 200 million metres per second) using optical fibres. This can be demonstrated by firing a laser pointer down a fibre optic cable and seeing it shine out the other end. Simply insert one end of the fibre optic cable into the recess of the laser pen bulb and turn it on.
Students will then be asked to send a message in Morse code down the cable to a person at the other end, turning the laser on and off (see the Morse code in the image below).
Figure 5: the morse code translates letters to dots • (short signal duration) and dashes — (long signal duration).
The activity shows that, by switching the laser on and off, you can now transmit digital information down the fibre at a very high speed. This can be used to transmit information in a binary format: when the light is off, that is a 0, and when the light is on, that is a 1 (note, though, that the light through real fibre optic cables flashes on and off thousands of times a second).
Figure 6: Laser light through an optical fibre. Credits: https://www.thefoa.org/tech/sciproj.htm
Discuss with students about how the SKAO dishes and antennae will be connected by a vast network of fibre optic cables to transfer data from the individual detectors to a central processing unit, where it is combined. This will make the SKAO work as a single instrument with better sharpness and a higher ability to detect faint signals than the individual antennas it consists of. The amount of data the SKAO network will have to carry is truly staggering. In the first phase alone, SKAO will produce 159 Terabytes of raw data per second, with information being transported down fibre optic cables as visible light. SKAO will use enough optical fibre to wrap around the Earth twice!
Health & Safety notice: use a class II (or weaker) laser pointer. Class II laser means the blink reflex is quick enough to protect the eye against damage from accidental exposure. However, eye damage could still occur from prolonged exposure, due to misuse of the equipment. You may wish the laser to remain permanently in the possession of a member of staff, or place it in a clamp stand pointing in a safe direction (and the fibre brought to the laser pen, rather than the other way around). You might also use signs warning people not to shine lasers in their eyes.
Activity 5: The importance of synchronisation
Students will try to play two identical sounds at exactly the same time, understanding how difficult this task is.
Use a sound system accepting two simultaneous inputs, connected to two mp3 players. The two mp3 players are in turn connected to one set of speakers. Each mp3 player should be loaded with the same sound file.
Ask students to try to press "play" on both mp3 players at exactly the same time, so that the sound files are played in sync, showing how difficult this task can be.
Note that there may be other ways of doing this, such as trying to play the same sound file on two different computers at exactly the same time.
In this activity, the mp3 players represent two dishes/antennae in the SKAO array and the speakers represent the central correlator.
In order for the SKAO to function as a single instrument, the signals from all the separate detectors must be synchronised to within 0.000000000001 of a second! Otherwise, the data will not be added up correctly. In practice, to sync the signals from the many hundreds of dishes, or hundreds of thousands of antennae, SKAO will make use of a very accurate time signal.
Health & safety notice: if the volume is too high, long-term exposure to loud sounds may cause discomfort or even hearing damage to participants, or those running the activity. This may be especially dangerous with both sets of this equipment running in a confined space. You may wish to prevent participants from changing the volume levels.
