Stage 2 – STEM Activity 10

Sundials and shadow clocks

A person is standing in the centre of a large circle, flat on the ground, in a park in daylight. The edge of the circle has flat stones placed at equal distances around it. There is a straight line going through the centre of the circle, extended through the top of the circle and the bottom of the circle. The person is standing up straight on the line going through the circle. The person’s shadow extends from the centre of the circle to the edge of the circle and beyond.

Description of activity

Students investigate ways that people have told the time throughout history. Students develop their knowledge of the Earth’s rotation around the sun and use this knowledge to investigate methods of telling the time without a watch. Students will compare the accuracy of their method compared to other chosen methods.

This activity will take approximately 3 hours:

research and modelling
design and build
collect data and review.

It is suggested that students work in groups of 2 or 3.

Context

Students observe angles, formed by shadows, and identify and classify them.

They observe and record changes in length and direction of a shadow during the day. Students will relate this to show how the movement of the Earth around the Sun can be used to measure time.

Outcomes

Skills

ST2-4WS investigates their questions and predictions by analysing collected data, suggesting explanations for their findings, and communicating and reflecting on the processes undertaken
ST2-5WT applies a design process and uses a range of tools, equipment, materials and techniques to produce solutions that address specific design criteria
MA2-1WM uses appropriate terminology to describe, and symbols to represent, mathematical ideas
MA2-2WM selects and uses appropriate mental or written strategies, or technology, to solve problems
MA2-3WM checks the accuracy of a statement and explains the reasoning used
HT2-5 applies skills of historical inquiry and communication

Knowledge and understanding

ST2-9ES describes how relationships between the sun and the Earth cause regular changes
MA2-6NA uses mental and informal written strategies for multiplication and division
MA2-7NA represents models and compares commonly used fractions and decimals
MA2-9MG measures, records, compares and estimates lengths, distances and perimeters in metres, centimetres and millimetres, and measures, compares and records temperatures
MA2-13MG reads and records time in one-minute intervals and converts between hours, minutes and seconds
MA2-16MG identifies, describes, compares and classifies angles
MA2-17MG uses simple maps and grids to represent position and follow routes, including using compass directions

Resources

Cardboard, rulers, pencils, straws
Model globe, lamp or torch, magnetic compass.

Work, health and safety

Check relevant Work, health and safety guidelines.
Students need to wear sun protection while monitoring the sun, and should not look directly into the sun.

Evidence of work for assessment purposes

An annotated, labelled diagram showing the development of the final design
A photo of their working model of a sundial
A written/verbal explanation of how the position of the sun allows an estimation of the time.

STEM teaching and learning activities

Students discuss how we experience day and night.
Students model the movements of the Earth, and sun to determine how day and night occurs.
Students observe the movement of the sun and shadows throughout the day.
Using the models of the Earth and the sun, discuss how the shadows change as the sun’s position changes.
Students explain that the changes from day to night are due to the Earth spinning on its axis.
Students research how telling the time has changed through history.
Students research the technology used to tell time, eg sundials, shadow clocks, hourglasses as well as the use of rocks, sticks and pyramids.
Students investigate how Aboriginal and Torres Strait Islander peoples maintain the skill to tell the time using the stars, tides and sticks.
Introduce the terms north, south, east and west, discuss with students where the sun rises and sets. Relate these directions to familiar objects in the playground.
Students design a device that can measure the passage of time, using the sun.
As the device will be situated outside, students must find a suitable place within the school that will show the passage of the sun. They will need to measure an area that will show the movement of the sun through the production of shadows.
Students discuss these designs with their peers to offer and take feedback to help improve their designs.
Students construct their device, working in groups.
Students monitor their devices each hour over a school day and record their observations.
Students record the time and the appearance of the shadows. Students may need to change their design to improve its accuracy. More advanced students may be able to mark hour intervals on the circumference of the circle in which the shadows fall.
Students compare the different devices and discuss the success of the devices. Discuss which devices were more accurate and why.

Vocabulary list

Axis – the line on which a rotating body, such as the Earth, turns
Gnomon – the raised part of a sun dial
Hourglass – an instrument for measuring time, consisting of two bulbs joined by a
narrow passage that allows sand to pass through slowly over a period of an hour
Revolution – when a planet or moon travels once around an object, eg the sun
Rotation – when a planet or satellite turns all the way around or spins on its axis
Sundial – an instrument that indicates the time of day by the position of the shadow, of the gnomon, as it is cast by the sun

Key inquiry questions

It is difficult for students to be convinced that the Earth spins (rotates) on its axis and that the Earth revolves around the sun because their experiences tell them that the Earth is stable and does not move (except, perhaps, in earthquakes). Scientists explain the relationship between the sun and the Earth by making many different observations.

How do shadows form?
Shadows form when solid objects block light rays. Light travels in straight lines but cannot pass through solid objects.

How does the length of a shadow change through the course of a day?
If the source of light is low, ie in the early morning and late afternoon, the shadows are long. The higher the source of light, the shorter the shadows become. Depending on where you are on Earth and what time of year it is, the sun may not be directly overhead at 12 noon. This relationship between the position of the light source and the length of shadow can be investigated using a torch.

Why does the shadow change direction and length?
The changing nature of the shadow is an indication that the source of light, the sun’s position in the sky, is changing.

Where does the sun rise and set?
Many children will have heard that the sun rises in the east and sets in the west. For many, this is evidence that the sun revolves around the Earth. While we can model that, it is the Earth’s counter-clockwise rotation and a static sun that causes this phenomenon, not all students will believe this and will persist in the belief that the sun revolves around the Earth.

The many pieces of evidence that show that the Earth revolves around the sun are too complex for this Stage. One of the easily observable pieces of evidence is that the sun does not rise exactly due east, except on the equinoxes, when day and night are equal duration, because the Earth’s equator passes through the plane of the centre of the sun. At other times, there is variation and students using a compass can observe this. Another piece of evidence is the observation of the sun at the North and South Poles where the sun may not rise for many months nor set for many months.

Additional information

The following statements outline some common preconceived ideas that many students hold, which are scientifically inaccurate and may impede student understanding.

Students often confuse the terms ‘revolve’ and ‘rotate’. When teaching young students about the Earth's movements, teachers may prefer to use the term ‘spin’.

Day and night are caused by the sun going around the Earth
See explanation above. A way to support the understanding that the Earth revolves around the sun is to role-play or make working models to indicate how the motion occurs. The Earth’s revolution around the sun causes day and night There are many preconceived ideas around the causes of the seasons. The Earth takes approximately 365 days to revolve around the sun. It is this motion that causes the seasons. The differences between the seasons are not caused by the Earth coming closer to or further away from the sun, but by the angle of tilt of the Earth.

The Earth is flat
Pictures of the Earth taken from Google Earth, the moon or space stations can support students understanding of the shape of the Earth.

Support materials

Teacher resources

Night and day: English for the Australian Curriculum resources for the improvement of English and literacy education
Six sundial projects for you to make
Sundials: how to make a simple sundial
Earth’s orbit and daylight: animations describing day, night and time

Student interactive

Light and shadows

Diversity of learners

For additional support

Carry out this task over a longer period, spanning different seasons to determine how the shadows change at different times of the year.

For extension

Students devise a way to calculate minutes or half hours to allow for further accuracy in telling the time.
Students research how telling the time has evolved over the centuries.
Task: You are allowed to go exploring for the day in the desert. You must be home by 2pm and have to make sure you eat and drink a litre of water every hour. You do not have a watch. Design and produce a device to monitor the time of day to make sure you are home on time.

Review

In this STEM activity, your students have explored the concepts of time, the motion of Earth and the position of Earth relative to the Sun. These ideas will be extended in Stage 3 with Earth’s place in the Solar System and they lead to further studies in Astronomy in Science Stages 4 and 5 and Physics Stage 6.

Your students have gained practical experience in designing, making and modifying a design plan. The use of a design plan and justification of changes to that plan develop critical-thinking skills. These skills are essential for studies in Technology (Mandatory) Stage 4. Providing and receiving constructive feedback and making modifications to address issues raised develops student resilience and a culture of being able to learn from one’s mistakes.