School days

— Christoph Saulder

Something people without family tend to forget is how early school starts. I had to be at the far end of the city at 8am on a June morning and I knew that it will take me almost an hour by public transport to get there. Patricia, a co-worker from ESO whose daughter goes to Colegio Dunalastair, was already waiting for me at the entrance with all the equipment I needed to perform the experiments during my talk. We then met with the teacher organising the event to prepare for the presentation in the school’s mess hall, which served as an auditorium for 115 elementary school students that day.

Even the teachers wanted to play!

My talk was titled: “The solar system and beyond”. Initially I was not sure how far beyond I can really go(!), given that my talk was limited to one hour (a long time, but there are many things to tell and show). Somehow I managed to complete the talk, which mainly focused on the solar system, on time. The talk itself was a kind of journey for the children starting at our sun, passing outwards through the solar systems and visiting every planet and other objects worth seeing. Next, we headed to the next stars and other solar systems with their exoplanets and finally reached out to the Milky Way, the Local Group and the entire Universe.

Practical science

The slides were mainly made up of pretty pictures and a few words and from time to time a simple illustrative sketch. Since 8-year old children would be unable to follow a one-hour power-point presentation, I performed some small experiments (a list of them can be found below) every two to four slides to maintain their focus. I only had a few experiments involving volunteers, but those were clearly the most popular.

Audience participation

During my talk, I tried to keep the children entertained by telling them scientific fun-facts such as:

— Saturn’s moon Titan ‘smells’ likes farts due to a significant amount of methane in its atmosphere!
— It takes one 38 million years to drive to the next star at the maximum permitted speed on a Chilean highway
— If the entire audience (roughly a hundred people) represents everything in the Universe, only 5 of them would be made of ordinary matter and only about half a student would be made of all the stars in the universe.

Astronomy basics with everyday equipment!

I expected the children to be baffled and speechless after this presentation, but almost every student in the auditorium had at least one question. Though most of them were just questions for basic facts, several were quite sophisticated such as questions about black holes, the habitable zone, other galaxies and some of them were beyond the today’s scientific knowledge, like “What caused the Big Bang?”. In the end the teachers had to stop the questions after about 20 minutes, because we ran out of time. Later I was told that the children were surprised that I was that young (just below 30), because they expected some old professor with grey hair and the looks of Einstein!



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List and short description of the experiments performed during the talk:


  • Distances in the solar system using a roll of toilet paper: drawing the sun to scale at the beginning and 10 sheet of toilet paper is 1 AU (distance Sun-Earth) and Neptune is at the end of the roll (300 sheets). The next star is 10000 rolls of toilet paper away from us.


  •  Sun spots using a lamp and some thick paper on a stick. By covering the lamp with a full sheet of the same paper, one can show that sun spots are not really black, but just darker then the rest of the sun.


  •  Illustrating Kepler’s laws using a cone of cardboard and a small ball. One can show that the ball runs faster, when it gets close to centre of the cone (=sun).


  •  Showing Venus as the evening star and the morning star by using 3 volunteers (Sun, Venus, Earth). Bind Sun and Venus together at about 1 metre distance and put Earth further away. Let Venus orbit the Sun and Earth spin about its own axis. Depending on which side of the Sun Venus is, it can be seen at sunrise or at sunset. It can never be seen at midnight (Earth showing her back to the Sun).


  • Using a grapefruit, a mandarin and a lamp to show and explain the phases of the moon as well as solar and lunar eclipses.


  •  Launching Sputnik. A simple tin-foil/paper model of Sputnik was made with an elastic band to represent Earth’s gravity and a volunteer was asked to launch it (eg. shoot it into the audience). One keeps holding the elastic band and swings it around, explaining the balance between the centrifugal force and gravity for satellites orbing Earth.


  •  Explaining the resonance gaps in the asteroid belt using a tiny swing and a tin foil asteroid. The swing was pushed regularly until the asteroid flew off.


  •  Explaining rotational flattening using a stick with a sphere made of a few paper stripes. Two sticks are taken, one with the sphere on top and one with a sphere on the bottom and the stick rolled between the palms of your hands, causing the sphere to flatten.


  •  Bags filled with sand representing how heavy 1kg would feel on the surfaces on all planets of the solar system and the moon.


  •  Creating impact craters using a bucket filled with flour and water (1kg flour for 2 litres of water) using a potato as an asteroid.


  •  Explaining the methods used to observe exoplanets using a lamp and a few other things. For transits, a cardboard planet on a stick was passed in front of the lamp. For micro-lensing I used my glasses (which were too weak to see it properly) and passed them in front of the lamp. For direct imaging, a fainter, small torch was put next to the lamp, and the lamp was covered with a cardboard circle. In order to demonstrate the radial velocity method, one can take the hands of a volunteer and let them move around you very rapidly. Lean back to keep the balance and thereby moving your head in tiny circles around its own ‘rotational axis’. Then one can explain that the star does the same due the gravity of the planet orbiting it and that this can be measured by Doppler shift (telling the usual story with the passing ambulance to explain the effect).


  •  Explaining why the Milky Way looks like a long band on the sky although it is actually a disk by showing a book edge-on and face-on.


  • Explaining the expansion of the universe by blowing up a balloon with galaxies drawn on it.


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