This unit builds toward these performance expectations:

• HS-ESS1-1 Develop a model based on evidence to illustrate the life span of the Sun and the role of nuclear fusion in the Sun’s core to release energy that eventually reaches Earth in the form of radiation.
• HS-ESS1-3 Communicate scientific ideas about the way stars, over their life cycle, produce elements. 
• HS-ESS1-2 Construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the Universe.
• HS-PS1-8✝* Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. 

*This performance expectation is developed across multiple units. This unit reinforces these NGSS PEs in a physics context.

†This performance expectation is developed across multiple courses. This unit reinforces or works toward these NGSS PEs that students will have previously developed in the OpenSciEd chemistry and/or biology courses.

ESS1.A: The Universe and Its Stars

• The star called the Sun is changing and will burn out over a lifespan of approximately 10 billion years. (HS-ESS1-1)
• The study of stars’ light spectra and brightness is used to identify compositional elements of stars, their movements, and their distances from Earth. (HS-ESS1- 2),(HS-ESS1-3)
• The Big Bang theory is supported by observations of distant galaxies receding from our own, of the measured composition of stars and non-stellar gasses, and of the maps of spectra of the primordial radiation (cosmic microwave background) that still fills the Universe. (HS-ESS1-2)
• Other than the hydrogen and helium formed at the time of the Big Bang, nuclear fusion within stars produces all atomic nuclei lighter than and including iron, and the process releases electromagnetic energy. Heavier elements are produced when certain massive stars achieve a supernova stage and explode. (HS-ESS1- 2),(HS-ESS1-3)

PS1.C: Nuclear Processes

• PS1.C.1: Nuclear processes, including fusion, fission, and radioactive decays of unstable nuclei, involve release or absorption of energy. The total number of neutrons plus protons does not change in any nuclear process.

PS3.D: Energy in Chemical Processes and Everyday Life

• Nuclear fusion processes in the center of the Sun release the energy that ultimately reaches Earth as radiation. (secondary to HS-ESS1-1)

Obtaining, Evaluating, and Communicating Information

Obtaining, evaluating, and communicating information in 9–12 builds on K–8 experiences and progresses to evaluating the validity and reliability of the claims, methods, and designs. The following elements of this practice are intentionally developed across this unit:

• 8.2 Compare, integrate, and evaluate sources of information presented in different media or formats (e.g., visually, quantitatively) as well as in words in order to address a scientific question or solve a problem.  
• 8.3 Gather, read, and evaluate scientific and/or technical information from multiple authoritative sources, assessing the evidence and usefulness of each source.
• 8.5 Communicate scientific and/or technical information or ideas (e.g., about phenomena and/or the process of development and the design and performance of a proposed process or system) in multiple formats (i.e., orally, graphically, textually, mathematically).

Elements from the following practices are also key to the sensemaking in this unit:

• Asking questions and defining problems
• Developing and using models
• Engaging in argument from evidence

Stability and Change. For both designed and natural systems, conditions that affect stability and factors that control rates of change are critical elements to consider and understand.

• 7.1 Much of science deals with constructing explanations of how things change and how they remain stable.  
• 7.3 Feedback (negative or positive) can stabilize or destabilize a system.  

Elements from the following crosscutting concepts are also key to the sensemaking in this unit:

• Patterns
• Scale, Proportion, and Quantity
• Energy and Matter

Which elements of NOS are developed in the unit?

• Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena: A scientific theory is a substantiated explanation of some aspect of the natural world based on a body of facts that has been repeatedly confirmed through observation and experiment, and the science community validates each theory before it is accepted. If new evidence is discovered that the theory does not accommodate, the theory is generally modified in light of this new evidence.
• Science is a Way of Knowing: Science knowledge has a history that includes the refinement of, and changes to, theories, ideas, and beliefs over time.
• Science is a Human Endeavor: Scientific knowledge is a result of human endeavor, imagination, and creativity.

This unit is anchored by historical accounts of stars that suddenly appear and then disappear a short time later. Students wonder about how some stars appear unchanging, while these stars change so drastically within such a short period of time. That gets students wondering about why stars shine and what could cause stars to change. They organize their questions in terms of matter, energy, and forces and decide to look more closely at the places in the sky where these historical events took place using modern technology. Students will come to figure out that these events are most likely supernovae, powerful explosions that signal the death of a massive star.

The supernovae phenomenon was chosen from a group of phenomena aligned with the target performance expectations based on the results of a survey administered to almost 1,000 students from across the country and in consultation with external advisory panels that include teachers, subject matter experts, and state science administrators. This phenomenon is aligned with space science content, pointing to complex cutting-edge questions about the nature of the Universe. The full physics course is designed to purposefully highlight a variety of different types of phenomena. While we design to privilege the interests of students to whom we owe an educational debt, we must not essentialize minoritized groups by assuming that a trend in the data equates to homogenous interests and experiences. Providing a diverse suite of entry points into content and practices creates more opportunities for every student to connect with the content.

The supernovae phenomenon was chosen for the following reasons:

• Students showed high interest across all demographic groups in explaining these events on the survey.
• To provide a diverse suite of entry points across the course, we were seeking a phenomenon that allowed students to consider abstract, cutting-edge science concepts in a context that is grounded in observations from Earth.
• Teachers and administrators saw the phenomenon as interesting and on grade band.
• Explaining the phenomenon requires the use of Earth and space science concepts and physical science frames.
• Explaining the phenomenon addresses all the DCIs in the bundle at a high school level.
• The phenomenon is complex enough to sustain student research on the internet without students feeling like one search answers the question.

This unit is the last in the OpenSciEd High School Physics course sequence and is designed to transition students out of K-12 science into the practices that they might engage with in their everyday life to figure things out, answer questions, and solve problems. It is designed to build on student ideas about energy transfer, unbalanced forces, and matter changes from the first five units of the course. In the first unit of OpenSciEd HS Physics, students developed ideas around energy transfer and conservation in the context of charged particles (electrons) colliding with other electrons (electricity) to transfer energy across great distances. In the second unit of the course, Earth science phenomena that transfer energy differently across scales of time and space motivated the need for forces to explain our observations. In the third unit, students developed a more robust understanding of forces as vectors and used conservation of momentum to make predictions about the outcomes of collisions. In the fourth unit, students expanded their model of forces to include forces of gravity at great distances, using ideas about fields developed in the first unit to understand the relationships between gravity and energy transfer. In the fifth unit, students use energy transfer, electromagnetism, wave mechanics, and forces at a distance to explain how food heats up in a microwave and if/how this technology might be dangerous for humans. In this unit, the final unit of the course, students will explore stars and cosmology, applying ideas about forces and energy from all five previous units on the largest scales.

The unit is organized into two main lesson sets. In Lesson Set 1 (Lessons 2-5), students investigate the question: How are stars born, and how do they die? Students investigate photos and spectra of the remnants of these events and then develop two sets of research questions to investigate in small groups. One round focuses on the matter and energy in stars and one round on the forces that are balanced within stars. Then students come to consensus in Lesson 5, modeling the feedback loop that maintains stability over most of the lifecycle of stars and what happens when the feedback loop is disrupted. Students’ small-group internet research is scaffolded by a set of tools that are introduced strategically across the lesson set: the Planning for Obtaining Information Tool, the Obtaining Information Tool, the Evaluating Online Sources Overview, and the Evaluating Sources of Information Tool. Students figure out that over millions or even billions of years, stars convert lighter elements like hydrogen and helium into heavier and heavier elements, and this motivates the next lesson set, as students wonder where these elements came from and how these matter changes could affect the matter in the Universe over time.

In Lesson Set 2 (Lessons 6-7), students investigate the question: How has the matter in the Universe changed over time? Students follow clues from spectra of the Universe to engage in a third internet research cycle, using the tools from Lesson Set 1, as well as a new one, the Planning for Communicating Information Tool. Using their research, they come to consensus around evidence for a hot dense Universe 14 billion years ago that has expanded into what we see today, a theory known as the Big Bang. Lesson 7 is intended to be the last lesson of the unit and the OpenSciEd High School Physics course and thus the last lesson of the OpenSciEd K-12 program. The lesson is designed to help students think metacognitively about the practices they have developed over the OpenSciEd High School program for asking and answering science questions and the crosscutting conceptual frames they can apply to help them make sense of what they figure out. They develop Driving Questions that they will not be able to answer in class but that students are encouraged to pursue answers to through independent online research, future science classes, a career in STEM, and/or a lifetime of curiosity.

This unit is already very condensed, spanning only 15 days. The following are example options to shorten or condense parts of the unit without eliminating important sensemaking for students:

• If you only need to develop disciplinary core ideas related to stars, you can end the unit after Lesson 5. We recommend that if you do this, you introduce the Planning for Communicating Information Tool currently in Lesson 6 in Lesson 4. You can still do Lesson 7 to complete the unit, including the transfer task, which does not focus on Big Bang related content from Lesson 6. This option will cut four days from the unit.

To extend or enhance the unit, consider the following:

• Give students more time to conduct their research in Lessons 3, 4, and 6.
• Pursue additional DQB questions as a fourth research cycle between Lessons 6 and 7.

• Laura Zeller, Revision Unit Lead, BSCS Science Learning
• Zoë Buck Bracey, Field Test Unit Co-Lead, BSCS Science Learning
• Michael Novak, Writer, Northwestern University
• Diego Rojas-Perilla, Writer, BSCS Science Learning
• Betty Stennett, Writer, BSCS Science Learning
• Jessica R Stephenson Reaves, SEEDS Consultant, Kennesaw State University
• Lizette Navarrete-Burks, SEEDS Consultant, University of Houston-Downtown

• Madison Hammer, Production Manager, University of Colorado Boulder
• Erin Howe, Project Manager, University of Colorado Boulder
• Amanda Howard, Copy Editor, University of Colorado Boulder

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by NextGenScience’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has been identified as a quality example of a science unit. You can find additional information about the EQuIP rubric and the peer review process at the nextgenscience.org website.