Pinpointing a fireball from two places
The question
How accurately can two observers find the position of a distant object using only compass bearings?
When a fireball is seen from two places, the directions each observer reports can be crossed on a map to find where it was. Camera networks use the same idea to work out where meteorites landed.
Equipment
- A large field and a tall marker such as a flag on a pole
- Two compasses or two protractors on boards lined up with a fixed baseline
- A tape measure or trundle wheel
- Squared paper, a ruler and a protractor
Method
- Mark two observing points 30 to 50 m apart and measure the distance between them. This is your baseline.
- A third person places the flag somewhere in the field without telling the observers where.
- Each observer measures the angle between the baseline and the direction to the flag.
- Draw the baseline to scale on paper, draw both angles and mark where the lines cross. Measure the real position of the flag and compare.
- What to measure
- The position predicted by your drawing, the real position, and the difference in metres. Repeat for several flag positions.
- How to present it
- Your scale drawings, a table of errors, and an explanation of how a longer baseline or more observers would improve the result.
- Take it further
- Find out why fireball reports always ask for the time, your exact location and the directions where the fireball started and ended.
Safety
Work in a school field or park with permission and an adult, away from roads.