Resources, planetary systems and astronomical scale
Evaluate resource trade-offs and distinguish evidence about planets, stars and galaxies from claims beyond the data.
What you will tackle
- Compare renewable and nonrenewable resources
- Use supplied planetary orbital data
- Distinguish planets, stars, galaxies and universe
- Interpret stellar-property and evolution models
Resources require a timescale
A renewable resource can be replenished on a relevant human timescale, but consumption can still exceed its renewal. Fossil fuels form over geological timescales and are nonrenewable on ordinary human timescales. Comparing resources involves energy output, land/water use, emissions and reliability; one favourable measure does not establish the best option under every objective.
Systems and scale
The Solar System includes the Sun and orbiting planets and smaller bodies. In visible-light observations, a planet mainly reflects starlight; planets also emit thermal radiation and do not sustain ordinary stellar hydrogen fusion. A star is a self-gravitating object whose properties depend on mass and evolutionary stage. A galaxy contains many stars, gas and other matter; the observable universe contains many galaxies. Earth's daily rotation and yearly orbit are different motions.
Read a supplied stellar model
In a simplified stellar-evolution model, stars form from contracting gas, spend a sustained phase powered chiefly by core hydrogen fusion and later follow mass-dependent paths. Colour/temperature, luminosity and size are distinct properties. Apparent brightness also depends on distance and intervening material, so a brighter-looking star need not be intrinsically more luminous. Orbital data can support relationships without proving a universal law from two objects.
Build your notes, then practise
Work on paper before opening an explanation. Guided tasks provide a starting point; independent tasks remove the scaffolding; application tasks ask you to justify a method or interpretation in context.
Guided practice
Guided 1
A wood resource grows by 40 units/year and is harvested at 55. Find its annual stock change and explain why renewable does not mean unlimited. Supplied planet data show A has period 1 year and B period 8 years; under T² proportional to r³ with rA=1, find rB.
Show a starting hint
Keep time and distance quantities distinct.
Compare with the explained answer
- Stock changes by 40 − 55 = −15 units/year despite replenishment.
- For the supplied orbital model, 8² = rB³, so rB = 4 in the stated distance units.
- The calculation depends on the supplied common-central-system model and does not convert period directly into a distance in years.
Answer / response criteria: −15 units/year; renewable can be depleted; orbital distance 4 units.
Independent practice
Independent 1
Place planet, star, galaxy and observable universe as system relationships using our Solar System as an example. Two otherwise comparable stars have the same intrinsic luminosity but one is farther away: predict apparent brightness under negligible absorption. Does their shared luminosity require the same radius?
Compare with the explained answer
- Earth is a planet orbiting the Sun, a star in the Milky Way galaxy, within the observable universe.
- The farther star appears dimmer under the stated conditions.
- Luminosity depends on size and temperature, so equal luminosity alone does not require equal radius.
Answer / response criteria: System relationships as stated; farther appears dimmer; radius is not fixed by luminosity alone.
Application practice
Application 1
Option A has lower emissions per kWh but lower dependable output during peak demand than B. Explain why selecting an energy resource needs an objective and more data. A supplied stellar model gives different late stages for low- and high-mass stars: why is a universal single end stage unsupported, and why does one image not directly show a star's entire history?
Compare with the explained answer
- Compare output needs, storage, land/water use and other constraints with emissions; the best choice depends on the stated objective and complete evidence.
- The supplied mass-dependent paths contradict a single universal end stage.
- An image records a limited observation; an evolutionary sequence is inferred from models and multiple lines of evidence, not directly watched in one exposure.
Answer / response criteria: Use explicit objectives and trade-offs; respect mass-dependent stellar paths and the distinction between observation and inferred history.
What can you explain now?
Option A has lower emissions per kWh but lower dependable output during peak demand than B. Explain why selecting an energy resource needs an objective and more data. A supplied stellar model gives different late stages for low- and high-mass stars: why is a universal single end stage unsupported, and why does one image not directly show a star's entire history?
Compare with the explanation
Use explicit objectives and trade-offs; respect mass-dependent stellar paths and the distinction between observation and inferred history.
Explain the reasoning before comparing. This review records your self-assessment rather than an official score or mastery decision.
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Source and review status
Coverage follows the named requirements and examples in the 2026–2027 ACT test guide and subject descriptions. That guide explicitly does not list every possible topic. The broader coded College and Career Readiness Standards are also mapped to conceptual teaching and practice; this does not calibrate a learner to a score band. The separate scientific-background context list and reading-complexity rubric have their own stated limits.
Original teaching and explained self-check practice are available. Specialist review and difficulty calibration remain pending. Essays require self-check or teacher review and are not automatically marked or awarded official scores.
Official source specification / guide