What the astro-lab Was

Before the pandemic, the astro-lab at the University of Cologne was a student laboratory focused on extrasolar planets. School groups — mostly secondary school students — came in and worked through a set of analogy experiments: how do you detect a planet you cannot see? How do you infer its size, its orbit, whether it might be habitable?

The pedagogical bet was that exoplanet research, precisely because it is headline-generating and genuinely open-ended, could counteract the motivational slump in physics that tends to set in around middle school. The context — life in the universe, habitable worlds, the possibility of something out there — did a lot of the work that no abstract force diagram could do.

The experiments themselves were analogy experiments: a lamp standing in for a star, a sphere on a track standing in for a planet. The key measurement was the transit: when the “planet” passed in front of the “star”, the light sensor registered a dip. Students measured the dip, estimated the ratio of areas, connected it to radius, and got a number that meant something. The number was not precise. It did not need to be. It was real.

Spring 2020

In March 2020, schools shut down, and the University of Cologne followed. Visits to the astro-lab were cancelled. The question the team faced — Alexander Küpper, André Bresges, and I — was not whether to do something but what was actually feasible.

German distance learning at the time was characterised by worksheet packages delivered to students with minimal interactive contact. Only 16% of German students reported being in video conferences with their teachers; 30% reported no contact at all since the initial shutdown. The infrastructure was not there, the habits were not there, and the expectation that students had the materials and equipment for a physics lab at home was not warranted.

What students did have, almost universally, was a smartphone.

Modern smartphones contain a remarkable array of sensors: ambient light sensors, accelerometers, gyroscopes, barometers, magnetometers. The app phyphox, developed at RWTH Aachen, makes those sensors accessible with a clean interface designed for use in education. If the sensor hardware was already in students’ pockets, the lab setup problem became: what household materials can stand in for the rest of the apparatus?

astro-lab@home: Bringing Science to the Sofa

The astro-lab@home project adapted the original lab experiments for home use with smartphones and everyday materials. The core transit experiment — measuring the dip in light caused by an opaque object passing in front of a lamp — turned out to be reproducible without any specialist equipment. A table lamp, a ball on a string, and a smartphone positioned beneath the lamp gave you the raw data. phyphox recorded the light curve in real time.

We designed the setup to be flexible enough to work with what students actually had. The default used the ambient light sensor in Android devices, which is directly accessible through phyphox. iPhones do not expose their light sensor through software interfaces, so for Apple devices we recommended an external Bluetooth sensor — an inexpensive workaround that also had the advantage of producing more consistent data across device types.

The resulting package was not just an equipment list. We developed accompanying materials that explained the physics (why does a transit produce a specific shape of dip rather than a sharp cutoff?), connected the analogy experiment to the real science (how does this scale up to the actual transit photometry done by TESS and Kepler?), and offered scaffolding at different levels of independence.

The project was published in the IAU’s CAPjournal in 2022 — a journal aimed at communicators and educators in astronomy. The audience was intentionally broad: teachers looking for accessible classroom activities, outreach organisations trying to reach students at home, curious individuals who wanted to do something real with their phone. “Bringing science to the sofa” was the headline, and that was genuine. The experiments worked in a living room.

What Came Next: astro-lab@school

When schools reopened and in-person teaching became possible again, the question was not simply “back to normal” but what the COVID period had actually taught us about the format.

The astro-lab@school, published in Astronomie+Raumfahrt in 2022, addressed that question directly. Some things from the home version had worked better than expected. The smartphone-based setup was cheaper, more portable, and more directly in students’ hands than the original benchtop apparatus. There was something pedagogically valuable about students using their own devices rather than lab equipment provided by someone else.

The astro-lab@school retained the smartphone-centred approach and adapted it for a school context: class sizes, time constraints, the reality of mixed equipment across a room of thirty students. The experiments from the home version were modified for group work and parallel execution. The scaffolding materials were reworked for the paced structure of a school lesson rather than the self-directed format of home use.

The result was not a reversion to the pre-pandemic lab. It was a hybrid: in-person group work, but with tools and methods developed for distributed individual use. The pandemic had, inadvertently, pushed the format toward something more robust.

A Note on What Made This Work

The core technical contribution — smartphones as measurement instruments for analogy experiments in astronomy education — is described in more detail in a later publication in The Physics Teacher, which covers the experimental setups, sensor comparison, and pedagogical progression in a form aimed at an international teaching audience. If you want the how-to, start there.

What I want to note here is something slightly different: the role of context.

The astro-lab bet on exoplanets as a motivational context, and the evidence supports that bet. Exoplanet research remains one of the few areas of physics that generates genuine public enthusiasm, and students' interest in the topic is empirically documented. What the COVID period showed is that the context is robust enough to survive the removal of the lab infrastructure. Students working on transit photometry with a lamp and a smartphone in their kitchen were doing the same thing, conceptually, as students at a benchtop sensor station at the university. The physical setup was different. The question was the same.

That is, I think, a more general lesson. Context-driven education is not dependent on a specific material configuration. The question carries.

For the curriculum unit that places these experiments in the context of the NRW Sekundarstufe I physics syllabus, see Fremde Welten. For the air pressure / Mars experiment that grew from the same lab, see Mission to Mars.

References

Spicker, S. J., Küpper, A., & Bresges, A. (2022). astro-lab@home — bringing science to the sofa. CAPjournal, 31, 12–17.

Küpper, A., & Spicker, S. J. (2022). astro-lab@school. Astronomie+Raumfahrt im Unterricht, 59(6).

Küpper, A., & Schulz, A. (2017). Das Schülerlabor astro-lab an der Universität zu Köln. Astronomie+Raumfahrt im Unterricht, 54(1).

Stampfer, C., & Staacks, S. (2020). phyphox — using smartphones as experimental tools. Physics Education, 55(5), 055007. https://doi.org/10.1088/1361-6552/ab8a2e

The Curriculum Problem

The 2019 revision of the NRW Gymnasium physics curriculum for Sekundarstufe I requires students to be able to describe, in broad outline, the typical stages of stellar evolution. This is new territory for many teachers — it is not a topic that would have appeared in teacher education programmes of ten or twenty years ago, and few teachers have personal experience with it from their own school or university courses.

More fundamentally: stellar evolution is a topic where the usual experimental approach does not work. You cannot compress an interstellar gas cloud in a classroom. You cannot observe a star form in real time. The timescales involved are tens of millions to billions of years; the spatial scales are measured in light-years and astronomical units. The experimental toolkit that works for optics, mechanics, and even much of electromagnetism simply does not apply.

This creates a genuine pedagogical challenge. Students have strong interest in astrophysical topics — the ROSE study documents this consistently — and stellar evolution involves physical concepts that are curriculum-relevant (gravity, pressure, energy, radiation). But the standard path from “concept” to “experiment” to “understanding” is not available in the usual form.

Two approaches are described here. One uses what students do have — smartphones and household materials — to model the physics of stellar formation through analogy. The other accepts that some physics is better learned through structured play, and designs accordingly.

DIY Experiments for Stellar Formation

The physics of star formation starts with an interstellar gas cloud and the competition between gravity and pressure. A cloud collapses when gravity wins: specifically, when the cloud is massive enough (or cold enough) that gravitational attraction overcomes the thermal pressure of the gas. This is the Jeans criterion, and it is the quantitative condition that separates clouds that will form stars from clouds that will disperse.

The qualitative version is accessible to secondary school students: a dense, cold, massive cloud is more likely to collapse than a diffuse, hot, small one. Once collapse begins, it is self-reinforcing — increasing density increases the gravitational attraction, which drives further compression, which increases the density further.

Two DIY experiments were developed to give students a physical encounter with the key concepts, using materials that can be assembled at home or in school without specialist equipment.

Experiment 1: Compression and heating. When a gas is compressed, it heats. This is directly measurable with the temperature sensor in a smartphone (or a separate Bluetooth thermometer connected to phyphox) and a simple compression apparatus — a syringe, a sealed container, or an inflation device. Students observe the temperature rise during compression and temperature drop during expansion, establishing the qualitative relationship. In the stellar formation context: the collapsing gas cloud heats as it compresses, which is why a protostar is hot long before nuclear fusion ignites.

Experiment 2: Self-reinforcing compression. A simple model of the positive feedback loop in gravitational collapse: a weighted ball in a flexible container, which compresses a small spring or air cushion. The more the ball compresses the cushion, the further it falls. Students can explore the threshold conditions under which the system reaches a stable equilibrium versus continues to compress indefinitely — a qualitative model of the Jeans criterion.

Both experiments are designed to be performed with available materials at the DIY/home level. The smartphone’s sensor integration via phyphox provides quantitative data where possible, maintaining the connection to real measurement that is a design principle across all the astro-lab experiments.

Why Stellar Evolution Is Hard to Experiment With

A methodological note worth making explicit: the shift from direct experiment to analogy experiment to board game is not a retreat from rigor. It is a recognition that different kinds of physical and conceptual content require different pedagogical approaches.

For exoplanet detection, we can build a genuine analogy: the physics of a planet blocking a star’s light and a ball blocking a lamp’s light are structurally identical. The analogy experiment produces data whose interpretation follows the same logic as the real scientific data.

For stellar evolution, the analogy is weaker. The compression of a gas syringe models one aspect of the collapse (temperature increase) but not the self-gravitating dynamics, the radiation pressure that eventually halts collapse, or the nuclear ignition that defines the transition from protostar to main sequence star. No tabletop experiment captures the whole process.

This is important to tell students: the experiment models this aspect, and not those aspects. Making the model limits explicit is part of the scientific literacy the unit is supposed to develop.

“Staub und Sterne”: A Board Game for Stellar Evolution

The board game “Staub und Sterne” (Dust and Stars), designed by Miriam Küpper and Alexander Küpper, takes a different route to the same content.

Games have been used in physics education in all phases of a lesson: as entry points (introducing a topic without immediately constraining it to a specific physical question), as vehicles for content acquisition, and as reinforcement and assessment tools. For stellar evolution specifically, the argument for a game is strong: the content involves a branching process with multiple pathways depending on a single initial parameter (mass), it is cyclic (the remnant of stellar death seeds the gas cloud that forms the next generation of stars), and it is inherently dynamic — the drama of a supernova is hard to convey through a diagram but easy to convey through play.

The target audience is years 7–8 (or year 8–9 depending on the school’s internal curriculum placement). The learning objectives:

• Describe the stages of stellar evolution as a function of mass
• Name the possible end states (white dwarf, neutron star, black hole) and the stellar paths that lead to each
• Describe stellar evolution as a cyclic process: the gas cloud produced at the end of a star’s life can, under the right conditions, seed the formation of new stars

The game “Staub und Sterne” (the name translates as “Dust and Stars”) has players navigating a star through its lifecycle, with the key branching decision determined by the star’s initial mass. A low-mass star follows one path; a high-mass star follows another. Both paths end in a stellar remnant and a dispersed gas cloud — raw material for the next cycle.

The game design incorporates the research on flow experience in learning: cooperative or competitive play, immediate feedback on decisions, the kind of engaged attention that is rare in conventional physics lessons and that the ROSE study data suggest is precisely what is missing for many students in physics classrooms.

A Note on What Experiments Cannot Reach

There is a broader point here that the exoplanet posts sidestep because the experiments for exoplanet detection are so unusually good. For most astrophysics — stellar evolution, galactic dynamics, cosmology — there is no analogy experiment that captures the full physics. The observable has been observed, the theory has been developed, but the pedagogical problem of how to give students a physical encounter with that knowledge remains genuinely difficult.

Games, simulations, interactive visualisations, and structural analogies all have a role. Each of them is a partial solution; none of them is what a well-designed experiment is. Knowing which approach fits which content, and being honest with students about the limits of the model you are using, is part of what physics teaching requires.

The experiments described in this post are a start on one small part of that problem.

The exoplanet experiments from the same project are described in the astro-lab@home, Hunting Exoplanets with Your Phone, and Fremde Welten posts.

The misconceptions students bring to stellar evolution — about the Sun, gravity, nucleosynthesis, and the language of astronomy — are documented in detail in Please Stop Saying the Sun Is on Fire, written as a companion to the September 2020 teacher training session that motivated much of this work.

References

Spicker, S. J., & Küpper, A. (submitted). Einfache DIY-Experimente zum Verständnis der Sternentstehung für den Physik- und Astronomieunterricht sowie zu Hause. Astronomie+Raumfahrt im Unterricht.

Küpper, M., & Küpper, A. (2022). Sternentwicklung spielerisch verstehen: Konzeption eines Brettspiels für den Physikunterricht der Sekundarstufe I. Presentation at AG Lehrerfortbildung, Universität zu Köln.

Elster, D. (2008). Was interessiert Jugendliche an den Naturwissenschaften? VFPC Verein zur Förderung des physikalischen und chemischen Unterrichts.

MSB NRW (2019). Kernlehrplan für die Sekundarstufe I — Gymnasium in Nordrhein-Westfalen: Physik. Ministerium für Schule und Bildung NRW.

Ward-Thompson, D., & Whitworth, A. (2011). An Introduction to Star Formation. Cambridge University Press.

The Problem With Air Pressure

Air pressure is one of those topics that students nominally know something about from everyday life and have almost always misconceived. The documented misconceptions are a long list: air is “empty” (nothing in it), air is weightless, air only exerts pressure when it moves (like wind), a vacuum “sucks” rather than being a region where surrounding air pushes in, and pressure increases with height rather than decreasing.

Some of these misconceptions are stubborn precisely because everyday experience seems to support them. Air does not feel like it has weight. A vacuum cleaner does feel like it is pulling. The atmosphere, experienced from inside it, does not announce itself as a pressure source.

The standard approach to this material — explaining atmospheric pressure, defining $p = F/A$, working through barometric altitude formulae — addresses the conceptual gaps at the declarative level. Students can recite that air exerts pressure in all directions. Whether they have actually updated their mental model is a different question.

“Mission to Mars” is a design-based attempt at conceptual change through physical encounter with the consequences of pressure differences.

The Context: Why Mars?

The motivation for choosing the Mars context was empirical, not poetic. The ROSE study — a large international survey of student interests in science — consistently finds that space, astronomy, and human exploration rank among the most motivating contexts for physics learning, for both boys and girls. Physics education research in Germany has known for decades that generic “physics” lessons underperform motivationally compared with context-embedded physics, and astronomy is one of the contexts with the clearest evidence base.

“Mission to Mars” asks students: a crewed mission to Mars would travel through the vacuum of space, with the crew living in a pressurised compartment. The compartment has to maintain atmospheric pressure while surrounded by near-vacuum. What happens if it fails? And how would you design a spacecraft structure to prevent that failure?

The question is concrete. The physics behind it — the difference between the pressure inside the compartment and the near-zero pressure outside, and the forces this pressure difference exerts on any structure — is the content of the lesson.

The Experiment

The full version of the experiment, as we ran it at the astro-lab at the University of Cologne, uses a vacuum pump, a bell jar, and a smartphone running phyphox. The smartphone’s built-in barometric pressure sensor records real-time atmospheric pressure inside the bell jar as the pump evacuates it.

Before building anything, students verify that the smartphone is a functional pressure gauge: they measure the current atmospheric pressure in the room and compare it with a provided reference value. This step matters pedagogically — it establishes that the phone is a real scientific instrument, not just a device for receiving worksheets.

Then comes the design-build-test cycle:

Design: Students are given PVC plumbing pipe sections, empty food containers, resealable bags, rubber bands, clamps, and other household materials. Their task is to build a prototype “spaceship” — a container that will maintain near-atmospheric pressure inside while the bell jar around it is evacuated to low pressure. The phone (or external sensor) goes inside the prototype to measure whether the prototype is holding.

Predict: Before testing, students are asked to state why they think their prototype will or won’t work. This surfaces their preconceptions in a low-stakes way and sets up the next stage.

Test: The prototype goes into the bell jar. The pump runs. The pressure sensor records. The light curve — sorry, the pressure curve — tells the story. Four outcomes are possible:

• Nearly flat line: the prototype is airtight, pressure inside stays near atmospheric. Mission success.
• “Bathtub” curve: a visible failure event — a cap pops off, the pressure inside drops sharply and then equalises. Students hear the pop. They did not expect the pop. This is the moment.
• Gradual decay: the prototype leaks slowly, the pressure inside drops steadily. Invisible failure.
• Noisy signal: something wrong with the setup.

The PVC pipe trap: the PVC pipe is deliberately included because it is the most impressive-looking material and is reliably incorrect. The friction between pipe and lid is insufficient at the pressure differences reached in the bell jar. The lid pops off. Students rebuild.

The Misconceptions, Addressed

The design-test-rebuild cycle forces students to confront the misconceptions listed above in a direct physical way:

Air is empty/weightless: handled in pre-activities with standard demonstrations (the dunked napkin, the deflated-vs-inflated balloon).

Air only exerts pressure when moving: the bell jar demonstration makes this concrete — the sensor shows pressure even in a static, undisturbed volume. When the pump evacuates the jar, the “stillness” of the remaining air doesn’t change its pressure.

A vacuum sucks: this is the crucial one, and the PVC lid pop addresses it more effectively than any explanation. The lid does not get sucked outward. The air inside the prototype at near-atmospheric pressure pushes the lid open against the external near-vacuum. When the lid fails and students hear the rush of air flowing back in after the valve is opened, the direction of the pressure force becomes viscerally clear: it was always the higher-pressure region pushing into the lower-pressure region.

The inquiry is scaffolded through worksheets and index cards, and there is a teaching assistant present in the lab version to catch dangerous situations (the smartphone can be damaged if exposed to too low a pressure — the instructions include a warning about testing pump suction strength before risking the device).

DIY Variants for School and Home

The full lab setup is expensive and not portable. One design principle we wanted to maintain was accessibility: the experiment should work at three budget levels.

Low budget (< $5): empty food containers connected to a household vacuum cleaner through a small hole. Works, no real-time measurement visible to students.

Mid budget ($5–$50): translucent storage containers in nested sizes (large = “space”, small = “spaceship”), a small sealing ring to connect the vacuum source. Students can watch the phone display through the container during evacuation. The vacuum achieved is lower than the lab version, but the qualitative experience — the prototype holding or failing — is the same.

Expensive ($500+): the full lab version with bell jar and diaphragm pump. Best analogy, best data, highest barrier.

The DIY take-home message, as the paper puts it: be creative, fail forward. Anything that creates some vacuum and fits a prototype counts.

The experiment adapts readily to e-learning contexts: each group builds a prototype, tests it (or has a family member film it), and presents the outcome — including why the first prototype failed and how the second was improved — in a shared video conference.

A Note on Where This Fits

“Mission to Mars” grew out of the astro-lab at the University of Cologne, the same student laboratory context as the exoplanet transit experiments. The common thread is not the specific physics topic (air pressure here, photometry there) but the experimental approach: smartphones as real measurement instruments, everyday materials as apparatus, an astronomical context that sustains engagement, and a design-build-test cycle that forces students to encounter the physics physically rather than only propositionally.

The air pressure content connects naturally to the exoplanet unit at a curriculum level: habitability of exoplanets depends partly on atmospheric pressure. In the Fremde Welten article, atmospheric pressure is listed as one of the factors that determine whether a detected exoplanet could support life — an explicit cross-link between the two units.

The astro-lab@home post describes how the broader astro-lab programme — including this experiment — was adapted for home use during the pandemic. The air pressure experiment is among the more challenging to replicate at home, but the low-budget vacuum cleaner variant makes a version of it possible.

The design-build-test structure of this experiment also ended up at the centre of a methodological argument during my thesis work. The short version: everyone told me to use grounded theory instead of design thinking as the research framework, and they were right to do so. That story is in a separate post.

References

Spicker, S. J., Küpper, A., & Bresges, A. (2022). Mission to Mars: Concept and implementation of a design-based (hands-on) smartphone experiment helping students understand the effects caused by differences in air pressure. The Physics Teacher, 60(1), 47–50. https://doi.org/10.1119/10.0009109

Küpper, A., & Schulz, A. (2017). Schülerinnen und Schüler auf der Suche nach der Erde 2.0 im Schülerlabor der Universität zu Köln. Astronomie+Raumfahrt im Unterricht, 54(157), 40–45.

Staacks, S., Hütz, S., Heinke, H., & Stampfer, C. (2018). Advanced tools for smartphone-based experiments: phyphox. Physics Education, 53(4), 045009. https://doi.org/10.1088/1361-6552/aac05e

Sjoberg, S., & Schreiner, C. (2010). The ROSE project: An overview and key findings. University of Oslo.

Changelog

• 2025-10-03: Updated the self-citation to the correct year (2022), volume/issue (60(1)), pages (47–50), and DOI (10.1119/10.0009109).