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No exams or lectures, but building a radio telescope with empty paint cans

No more lectures and exams for the Radio Astronomy course taught by Michiel Brentjens. The corona crisis is a moment of reflection that has changed his whole way of teaching. Instead of being in front of the class, he lets his students build a radio telescope with paint cans.

Three years ago, Brentjens took over the course from his colleague. Together with co-teacher Timothy Shimwell, he then starts giving lectures and a computer practical on the history, operation and use of radio telescopes.  'At the end of the year I realised there was far too much passive listening. The students also said that the classes did not prepare them well for the exam and they were right about that. At an exam, you have to make written exercises on paper and we didn't really practice that.'

Preparing lectures takes a lot of time and effort for the lecturer, but according to Brentjens, students learn relatively little from it . 'If you listen the whole time, you only remember a small part of all the information that passes. We then changed half of the lecture into practising with written exercises. That worked quite well, but then corona came along and everything had to be done at home.'

In those few hours, they connected a lot of knowledge in a fun way.

New approach due to corona

Brentjens soon realises that it is difficult for the students to stay concentrated behind a screen for an entire class. To keep the students actively involved, he and Shimwell record the lectures in small chunks and hold quizzes in between. For the last class of the course, a lecture by Jim Moran from the United States was planned. As this was not possible anymore due to the pandemic, Brentjens came up with a nice alternative.

Radio telescope to photograph a black hole

‘With a short article on how to build a radio telescope to photograph a black hole, I wanted students to work in small groups. Everyone was given a component to work on. They had to fall back on each other for more information and complement each other’s work. In that assignment everything from the entire subject came together.’

Brentjens loved that afternoon. ‘It was great to be doing something together. In those few hours, they connected a lot of knowledge in a fun way. And I had a lot of fun too. I thought: this is really cool!’

Building a radio telescope with paint cans

From that moment, Brentjens plays with the idea of having the students build a radio telescope in real life. 'I thought: what if I were to teach a course that doesn’t include an exam and lectures? The two things that define a university.' Because materials for an antenna are extremely expensive, he searches the internet for alternatives. 'It turns out that five-litre paint cans are almost exactly the right size to detect the radio radiation from neutral hydrogen gas in the universe.'

With €4 paint cans, a cheap radio receiver and a precision clock donated by ASTRON, the plan comes to life. When the first students arrive, they are very surprised to see materials on the table. 'I thought we were going to build a telescope in our heads,' said a student.

Although the way of learning is different now, the students still have to learn the same subjects. 'I hate exams and so do you, but you still have to be assessed. So you're going to have to work hard,’ Brentjes said.

Michiel Brentjens in the studio room where the practical lessons take place

Applying abstract concepts in practice

Before each class, the students have to prepare themselves extensively. 'For the first one, they had to work eight hours already. Instead of a history lesson on radio astronomy, they had to make a list of the most impactful articles in the field from 1930 to the present. During the class, I had them discuss which discoveries were the most impactful. In this way, they went through the entire history in one interactive lesson.'

Then comes the real work: getting to work in groups to build the radio telescope. The students learn everything about the subject by doing it. 'One group showed a different graph on their screen during a class than the screen of the other group. They went investigating the difference and found out that one group was closer to the monitor on the wall. In this way they learn abstract concepts such as noice using practical examples.'


'During a regular lecture, you see everyone slacking off ten minutes before the break. Now they are so busy that I have to remind them to eat once in a while.

Students almost forget to take breaks

Classes go well and the groups are very busy every week. 'During a regular lecture, you see everyone slacking off ten minutes before the break. Now they are so busy that I have to remind them to eat once in a while.'

Later in the series of classes, the students go outside to calibrate their paint cans. 'That was great fun, going outside like that. Of course, the students have to be assessed for the subject as well. Therefore, the teachers have the students assess each other. 'The university was a bit panicky when they heard that. Now agreements have been made that we teachers are ultimately responsible for the grades. But we actually see that students grade each other as we would do ourselves. Usually even a little stricter.'


Detecting the sun and the Milky Way with paint cans

Students generally react well on this new way of learning. Sometimes they find the preparation a bit too much work. Therefore the teachers will take a critical look at the course in order to make it even better for the next groups. 'Some students also had some trouble with factual correctness. I can give students an A for a report that contains nonsense in a few places. It is the method, structure and the figures that reflect the process very well. That is more important than the correct answer.'

The final assignment of the course was initially still the same as before in which students had to work with existing data packages. Following a question of a student, some of them were allowed to continue with the paint can-telescopes. 'They ran into all sorts of problems and did a lot of extra tests. In the end, there are clear indications in the data that they have succeeded in detecting the sun and the Milky Way.'

Pupils take measurements with the paint cans in the open air

'Corona has turned my entire teaching practice upside down and that's great!

Telescopes are just a big set of paint cans

After the pandemic Brentjens wants to continue with this way of teaching. 'Corona has turned my entire teaching practice upside down and that's great! In a lecture you are sometimes pouring out information instead of transferring knowledge. This new way of working forces you to look at what you really want to teach. In my opinion, we have gone much further towards the essence of the subject.'

The students now not only remember the knowledge better, but they also understand other things. 'The fact that they can relate it to the things in the world around them certainly helps. Later, when they start working with the big telescopes, they see that they are actually just a big set of paint cans as well.'

For other lecturers who struggle with lectures, Brentjens still has a tip. 'Look at what you want the students to be able to do. If you want them to write better software, let them practice writing software during the course. What has worked well for me is to focus more on teaching good habits and processes rather than hammering away at the factual details.'

Do you teach and do you want to see if you can do things differently? Please contact SEEDS@science.leidenuniv.nl. Our educational and technical experts will be happy to help you.

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