Investigating Science 11–12 · Year 11

Testing the assumption that the Sun rises in the east

Module 2: Cause and Effect – Inferences and Generalisations

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

The Sun rises due east only at the equinoxes; on other dates the rising point swings north or south by an amount set by latitude and the Sun’s declination.

What you need

a vertical 1 m stick checked with a plumb line, chalk or pegs, to find true north from the shortest noon shadow
a sighting board with a large protractor aligned to true north, placed with a clear eastern (or western) horizon
sunrise or sunset times for the site from the Geoscience Australia calculator, a record sheet for six or more weeks

How to do it

Mark the tip of the stick’s shadow every few minutes around midday; the shortest shadow points to true south, so the opposite direction is true north. Align the protractor with it.
Once a week, at the published time, record the bearing of the point on the horizon where the Sun’s upper edge first appears (or disappears at sunset), using a landmark rather than looking at the Sun.
Continue for at least six weeks, ideally spanning an equinox.
Write the assumption as a testable hypothesis and compare every bearing with 90 degrees and with the model value for the date.
Explain any difference between measured and model bearings (horizon height, refraction, reading error).

What you should see

For Sydney (33.87° S), cos A = sin δ / cos φ gives a sunrise bearing of 61.4° true at the June solstice (δ = +23.44°), 28.6° north of east; 90.0° at the equinoxes; and 118.6°, 28.6° south of east, at the December solstice. Near the September equinox the bearing moves about half a degree south each day: the model gives 91° on 23 September, about 98° on 7 October, 104° on 21 October and 110° on 4 November. Allowing for refraction and the Sun’s semidiameter (h₀ = −0.833°) shifts each bearing by about 0.6°, smaller than a protractor reading error. The weekly bearings reject the assumption for every date except near the equinoxes.

What changes

What you change: date
What you measure: bearing of sunrise or sunset
What you keep the same: same observing position and protractor alignment
same event (first appearance of the upper edge)
true north from the noon shadow

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

The Sun always rises exactly in the east and sets exactly in the west.
The Sun is directly overhead at noon everywhere.
A compass needle points to true north.

Safety card

Low riskLearners carry it out

Hazards

eye damage from looking at the Sun
early-morning or evening travel to the site

Controls

never look directly at the Sun or through any optical aid; read the bearing from the landmark
observe from home or school grounds with family or school permission

Note

No hazardous chemicals or heat sources: record the activity in the school's RiskAssess risk assessment, following the NSW Department of Education Science safety and compliance page; the Chemical Safety in Schools package is not triggered.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-9 INS11/12-1 INS11/12-2 INS11/12-4
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities