Science 7–10 · Year 7

Shadow stick: tracking the Sun across a school day

Science understanding: Earth and space sciences (ACARA places Earth's rotation and day and night in Year 6, AC9S6U02; the Year 7 content description AC9S7U03 is met through the seasonal change in the noon shadow; NSW Stage 4 focus area: Observing the Universe)

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The idea

Earth's rotation carries the Sun across the sky, so a vertical stick's shadow swings and shortens to a minimum at solar noon, which is not 12:00 by the clock; the length of that noon shadow changes with the seasons because Earth's tilted axis changes the Sun's noon height.

What you need

1 vertical stick or dowel, 30 cm, fixed upright on a level board (check with a spirit level)
1 sheet of A2 paper or a concrete surface with chalk
1 metre ruler and 1 protractor
1 magnetic compass (note the local magnetic declination from the compass card or a map legend)
1 clock set to local time; 1 recording table with columns time, shadow length, shadow bearing

How to do it

Set the board in full sun from before 9:00 and leave it fixed all day.
Every 30 minutes from 9:00 to 15:00 mark the shadow tip, record the time, measure the shadow length from the stick base and the bearing of the shadow with the compass.
Plot shadow length against clock time and read the time of the shortest shadow; that is local solar noon.
Compute the Sun's altitude at each mark from tan(altitude) = stick height / shadow length.
Compare the noon shadow with one from another season: repeat on a second day later in the unit, use a class record from a different date, or read the NOAA Solar Calculator's noon altitude for 21 June and 21 December; two boards on the same day show measurement scatter.

What you should see

Shadow length falls to a minimum near the middle of the day and for most of the year the bearing sweeps from west of south through south to east of south in Sydney (shadows point south of the stick in the southern hemisphere, so the Sun is in the north at noon). In the weeks around the December solstice (late November to the end of January, with daylight saving) the Sun is still south of due east at the first readings: on 21 December it passes due east 3.3 hours before solar noon, about 9:34 by the clock, so the 9:00 shadow points north of west before swinging round through south. The noon shadow gives the Sun's noon altitude: at the equinox the computed altitude at Fort Denison (latitude 33 degrees 51 minutes S) is 90 - 33.85 = 56.15 degrees; on 21 June it is 32.7 degrees and on 21 December 79.6 degrees (obliquity 23.44 degrees). Solar noon in Sydney falls between about 11:39 and 12:09 standard time across the year: Fort Denison (longitude 151 degrees 13 minutes E) is 4.9 minutes of time east of the 150 degree meridian, and the equation of time moves noon up to about 16 minutes earlier (early November) and about 14 minutes later (mid February). It is about an hour later by the clock when daylight saving applies; the NOAA Solar Calculator gives the exact figure for the date. The learner knows it worked when the shortest shadow points due south and its altitude agrees with the calculator within 2 degrees.

What changes

What you change: time of day (and date, if repeated)
What you measure: shadow length and shadow bearing
What you keep the same: stick height
board level and position
measuring method

Common misconceptions

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

The Sun is highest at exactly 12:00 by the clock.
Shadows point north at noon everywhere; in Australia the noon shadow points south.
The Sun moves across the sky; it is Earth turning that moves the shadow.

Safety card

Low riskLearners carry it out

Hazards

sun exposure over a full day of readings
never look directly at the Sun

Controls

hat, sunscreen and shade between readings
readings take under a minute each
no optical aid pointed at the Sun

Note

No hazardous chemical and no flame or heating apparatus: a generic classroom risk assessment (CSIS 1.7 or RiskAssess) covers trips, spills, warm lamps and sharp edges.

Curriculum references

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

Science 7-10 Syllabus (2023), NSW Education Standards Authority (implemented from 2026; codes read at curriculum.nsw.edu.au on 22 and 23 September 2026)SC4-OTU-01 SC4-WS-01 SC4-WS-04 SC4-WS-05
Australian Curriculum v9AC9S7U03AC9S7I03AC9S7I04

Sources

The pages the author read to write this activity.

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