Why it matters
A measured reference stick and its shadow create a proportion with the target and its shadow. The method fails when ground slopes differ, a shadow tip is hidden, or observations are far apart in time.
What you’ll need
Tools
- Straight measuring stick
- Tape measure
- Notebook
Materials
- Safe level observation area
- Sunlit target with visible shadow
Before you begin
Safety & limits
- Do not enter a roadway, water, unstable ground or a restricted site to reach a shadow tip. This is an estimate, not a structural survey.
- Avoid looking directly at the Sun; measure shadows on the ground.
Work carefully, in order
The method
- 01
Choose a safe moment
Find a target with a visible base and shadow tip on approximately the same level surface as a vertical reference stick. If those conditions fail, use another method.
- 02
Measure the reference
Measure the stick height from the ground and its shadow length in the same units. Keep it vertical and mark the shadow tip while the Sun is steady.
- 03
Measure the target shadow
Measure from target base to shadow tip as close in time as practical. Note any slope or obstruction that could distort the comparison.
- 04
Compute the proportion
Use target height = reference height × target shadow length ÷ reference shadow length. Record all values with units and show the calculation.
- 05
Check the result
Compare with a known scale such as a doorway or a map, and label the result approximate. Repeat if the shadow moved or a measurement is uncertain.
Mistakes to avoid
- Using an inclined stick
- Measuring shadows at different times
- Applying the ratio across unequal slopes without correction
If it isn’t working
The shadow tip is unclear
Do not guess a precise value; change time or target, or report a range.
The reference shadow is very short
Wait for a longer measurable shadow to reduce relative error.
Then & now
Historical context
Surveyors and travelers used shadow geometry long before electronic rangefinders; it remains a good check of how measurements and assumptions interact.
The modern equivalent
A clinometer or laser rangefinder can assist where its instructions and site access permit.
Sources & review
Editorial draft — specialist review pending. Written 2026-09-24. Sources support the stated scope; this page has not been professionally certified.
- NASA — Earth Observation Camp ↗
Compare a measured vertical object and its shadow using similar triangles. Checked 2026-09-24.
- NIST — Metric Ruler ↗
Estimate a length first, then check it with a metric ruler. Checked 2026-09-24.
