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.