Measure a tree with its shadow
Forty-five minutes on a sunny day. Use a stick, a tape measure and a little arithmetic to find how tall a tree is without climbing it.
- Time
- 45 min
- Cost
- $0
- Ages
- 8 and up
- Where
- Open ground with a tree
Since 1911: The shadow method works the same as in 1911. The sound rule needs one change: sound travels about a mile in 5 seconds, so the National Weather Service tells you to count the seconds from flash to bang and divide by 5. If thunder follows within 30 seconds, go indoors.
What you need
- A straight stick or broom handle about 3 feet long
- A tape measure or a 3-foot piece of string to measure with
- Chalk, small stones or sticks to mark shadow tips
- Paper, pencil and a phone calculator
Before you start
- Don't climb the tree or lean ladders on it. This plan keeps your feet on the ground.
- Stay away from roads and driveways when you measure shadows. Pick a quiet spot.
- If thunder rumbles, stop and go indoors. Don't finish the measurement.
Steps
- Pick a sunny day and a level spot. Choose level ground in morning or afternoon sun, with the whole tree shadow on flat ground.
- Stand the stick up. Stand the stick upright and measure its height.
- Measure the stick's shadow. Mark the stick's shadow tip and measure the length.
- Measure the tree's shadow, now. Right away, measure the tree's shadow from the trunk base to its tip.
- Work out the height. Tree height = tree shadow × stick height ÷ stick shadow.
- Compare guesses. Compare the guesses with the answer and measure a second object.
If it stalls
- If the stick won't stand, hold it against a post or have the kid hold it straight.
- Measure both shadows within a couple of minutes. The sun moves.
Height guess vs. measured
Signed off: can do this.Signed by Date