Australian Curriculum v9 / ACiQ Year 7 Science - Unit 9 - Eclipses, tides and scientific models

Eclipses, tides and scientific models

Use and evaluate Earth-Sun-Moon models to explain eclipses and predictable tidal patterns.

Updated 2026-07-24 - 10 min read

Use and evaluate Earth-Sun-Moon models to explain eclipses and predictable tidal patterns. This note connects the core scientific model to a worked example, an inquiry design and the limits of the evidence.

Core model

Eclipses require both the correct phase and close three-body alignment. Tides reflect gravitational effects, Earth’s rotation and local ocean geometry. Scientific models explain selected patterns but simplify scale, orbit tilt and coastlines.

Accessible diagram description: Solar eclipse text line: Sun → Moon → Earth, Moon's shadow on Earth. Lunar eclipse: Sun → Earth → Moon, Earth's shadow on Moon. A separate top view shows aligned positions for spring tide and a right angle for neap tide.

A model is useful because it highlights relationships that help explain or predict evidence. It is not a perfect copy of reality. Always state what the representation includes, what its arrows or symbols mean, and one relevant limitation.

Authored representation workshop

Eclipse and tide alignments

Accessibility description: Solar eclipse alignment is Sun, Moon, Earth. Lunar eclipse alignment is Sun, Earth, Moon. Spring tides use a near-straight Sun-Earth-Moon alignment; neap tides use roughly right-angle Sun-Earth and Moon-Earth directions. The Moon's orbit is tilted, so most new and full Moons miss exact eclipse alignment.

Represented parts

  • Sun
  • Moon in solar-eclipse alignment
  • Earth receives Moon shadow
  • Earth in lunar-eclipse alignment
  • Moon receives Earth shadow
  • Quarter-phase Moon at right angle for neap tides

Represented relationships

  • Sun -> Moon in solar-eclipse alignment (light)
  • Moon in solar-eclipse alignment -> Earth receives Moon shadow (Moon shadow)
  • Sun -> Earth in lunar-eclipse alignment (light)
  • Earth in lunar-eclipse alignment -> Moon receives Earth shadow (Earth shadow)
  • Earth receives Moon shadow -> Quarter-phase Moon at right angle for neap tides (roughly 90 degrees)

Learner action: Use the nodes to construct both eclipse orders and both tide geometries. Then revise a flat-orbit model by adding orbital tilt and explain which observation the revision accounts for.

One harbour's tidal range across lunar phases

Accessibility description: Ranges are larger near new and full Moon and smaller near quarter phases. Weather can create short departures from this repeating pattern.

| Lunar phase | High water (m) | Low water (m) | Tidal range (m) | Conditions | | --- | --- | --- | --- | --- | | New Moon | 2.5 | 0.3 | 2.2 | calm | | First quarter | 1.8 | 0.8 | 1.0 | calm | | Full Moon | 2.4 | 0.3 | 2.1 | onshore wind | | Third quarter | 1.7 | 0.8 | 0.9 | calm |

*Range equals high water minus low water at the same harbour.*

Learner action: Use official or teacher-supplied tide data only; no shoreline visit is required. Recalculate each supplied tidal range, compare aligned and quarter phases, identify weather as a possible local influence, and evaluate what one-harbour data can and cannot establish about the alignment model.

The representation and table are supplied evidence. Do not replace a represented value, relationship or anomaly with an expected result. If a visual version is created, preserve this text-equivalent information and define every symbol, arrow, heading and unit.

Worked example

The reasoning routine is:

  1. identify the observation, measurement or represented relationship
  2. select the relevant science idea
  3. connect the idea to the evidence in a complete sentence
  4. qualify the answer when the evidence or model has a boundary

Inquiry connection

Question: How does tidal range at one harbour vary across a lunar month?

Reasoned hypothesis: If the Sun, Earth and Moon are more closely aligned near new or full Moon, tidal range will be larger than near quarter phases.

  • Independent variable: lunar phase or alignment date
  • Dependent variable: daily tidal range
  • Relevant controls: harbour, tide-gauge source and range calculation
  • Hazard: collecting shoreline observations near changing water can involve drowning and slip risks
  • Risk control: use official tide data or observe only from approved supervised locations away from water edges
  • Reproducibility detail: cite harbour, dates, gauge, time zone and high-minus-low calculation

Possible data finding: ranges were largest near new and full Moon and smallest near quarter phases, with weather-related departures on two days.

Evidence-based interpretation: The repeating pattern supports the alignment model, while weather helps explain short-term anomalies.

Limitation: One harbour's local geometry means exact heights cannot be generalised to every coast.

This investigation frame recurs across Year 7 Science. A sound response names a testable relationship, matches the hypothesis to the same variables, manages a realistic risk, specifies quantities and measurement rules, analyses the full data pattern, supports a claim with evidence and states what the evidence cannot establish.

Science as a human endeavour — AC9S7H01

A simplified flat-orbit model predicts an eclipse at every new and full Moon. Supplied observations show that most new and full Moons have no eclipse. A revised model adds the Moon's tilted orbit and predicts eclipses only when the required phase occurs near an orbital crossing. Explain how the supplied evidence requires the model to be revised, compare what each model can explain, and identify further evidence that could test the revised model.

Protocol and evidence boundary: Use only the supplied model predictions and observations. Treat both models as purpose-built representations, distinguish evidence from inference, and do not claim that revising the first model means earlier scientific work was careless or useless.

This is a rubric-guided activity, not an automatically scored mastery item.

  • Original model and prediction: States the flat-orbit model's assumption and the monthly-eclipse prediction that follows from it. Revise if needed: Connect the original assumption to a testable prediction.
  • Conflicting evidence: Uses the absence of most predicted eclipses as evidence that the original model is incomplete. Revise if needed: Name the observation that the original model cannot explain.
  • Evidence-driven revision: Explains how adding orbital tilt changes the prediction and why the revised model better matches observations. Revise if needed: Show how the new feature resolves the evidence conflict rather than merely naming tilt.
  • Qualified evaluation: Identifies a strength and limitation of the revised model and proposes relevant further observational evidence. Revise if needed: Evaluate the revised model's boundary and state how it could be tested again.

Common errors and corrections

  • Error: Predicting an eclipse at every new or full Moon. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Assuming a simple global tide model predicts the same height and timing at every coast. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Claiming the Moon alone determines every local tide without a solar or coastal contribution. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Treating a simplified model as a scale-perfect copy of reality. Correction: Return to the core model and identify the exact evidence or relationship before answering.

Practice

  1. Identify two eclipse alignments.
  2. Explain the orbit-tilt condition.
  3. Calculate tidal range from a table.
  4. Infer spring or neap conditions and state one local limitation.

Transfer task

Apply the topic to the investigation below without relying on a teacher or AI to mark the reasoning.

Evidence status: activity only. Use the task-specific rubric below for self-review or teacher feedback; completion does not automatically award mastery.

Context: How does tidal range at one harbour vary across a lunar month?

  1. Rewrite the question if it does not clearly name the relationship and measurable outcome.
  2. Write the matching reasoned hypothesis: include the expected direction and the science idea that justifies it.
  3. Identify the independent variable, dependent variable and at least three relevant controlled variables.
  4. Write a six-step reproducible method. Include equipment, quantities, units, an ordered measurement rule and at least three repeated trials for each condition.
  5. State the hazard, possible harm and a practical control. The control must address the stated hazard rather than being generic advice.
  6. Design a results table with headings and units. State which graph or other representation would best show the relationship and why.
  7. Use this possible finding: ranges were largest near new and full Moon and smallest near quarter phases, with weather-related departures on two days. Describe the overall pattern, identify any anomaly and state a reasonable check.
  8. Write a conclusion using claim, specific evidence and scientific reasoning. Finish with this limitation: One harbour's local geometry means exact heights cannot be generalised to every coast.

Correction guide: Compare the question and hypothesis to confirm they use the same two variables. In the method, circle every quantity and unit and underline every controlled condition. In the data response, separate the broad pattern from any anomalous result. In the conclusion, highlight the evidence sentence and box the limitation. If one of these parts is absent, revise that part before checking the scientific vocabulary.

An excellent transfer response is precise without pretending the evidence is perfect. It makes the chain from question to method to data to claim visible, and it explains how the core model applies in the unfamiliar context.

Task-specific inquiry rubric

  • Question and hypothesis for lunar phase or alignment date and daily tidal range: Names the same measurable relationship in both and gives a scientific reason. Revise if needed: Align the changed factor, measured outcome and predicted direction.
  • Fair, safe and reproducible method: Controls harbour, tide-gauge source and range calculation, manages "collecting shoreline observations near changing water can involve drowning and slip risks", and specifies quantities, units, measurement rules and repeats. Revise if needed: Replace vague directions and generic safety advice with operational detail.
  • Data and analysis plan: Provides labelled headings and units, an appropriate representation, a way to describe the whole pattern and a rule for checking anomalies. Revise if needed: Show how evidence will answer the question before collecting it.
  • Scientific interpretation and boundary: Links the expected evidence to eclipses, tides and scientific models and anticipates this boundary: One harbour's local geometry means exact heights cannot be generalised to every coast. Revise if needed: Explain the science link and state what the design cannot establish.

Self-check

For each response, check:

  • Did I use the correct scientific vocabulary?
  • Did I refer to the specific evidence, feature or data?
  • Did I explain the link rather than only naming it?
  • Did I avoid claiming more than the model or data support?
  • If an investigation is involved, did I address question, hypothesis, variables, safety, reproducibility, data, evidence and limitations?

Sources