A Shadow Compass
Geometry & Trigonometry
How to create a shadow compass in the Northern Hemisphere.
Where this idea comes from
Start here — this is the source that inspired this exploration.
Introduction
A stick pushed vertically into the ground casts a shadow that moves as the Sun moves across the sky. Marking the tip of the shadow at intervals and joining the marks gives a line that runs close to east-west, which lets you find a rough compass bearing without any instruments. This method is approximate rather than precise, but it works because the Sun's position changes predictably through the day and with the seasons. This exploration asks you to test the method, predict shadow lengths with trigonometry, and check how the method changes with season and latitude.
Guiding Questions
- At what time of day does a stick's shadow point exactly north (in the northern hemisphere)?
- Mark a shadow tip every 15 minutes. What curve does it trace, and how do you find the north-south line from it?
- Use trigonometry to predict the shadow length for your latitude and date. Do measurements agree?
- How does the method change with the seasons — and would it work near the equator?