1. Parallax TheAnomalyInfinite

2. Triangulation Surveyors use triangulation to measure unknown distances. –Base distance –Angles A and B base A B distance

3. Earth’s Size Triangulation was used to measure the Earth –Eratosthenes in 200 BC –Parallel rays from the sun casting a shadow Earth Alexandria angle = 7° 12’ Syene angle = 0° 500 miles 7° 12’ is 1/50 of 360° 500 miles is 1/50 of 25000 miles

4. Common Base If the base is fixed, the distance is measured by the angle. baseangle Aangle B

5. Apparent Shift A moving observer sees fixed objects move. Near objects appear to move more than far objects. Telephone poles whip by faster than distant trees. The effect is due to the change in observation point, and is used by our eyes for depth perception. base angle A angle B

6. Observing Parallax Observe an object against the background. Shift one seat left and observe again. Subtract to get the parallax shift. 05101520253035404550

7. Measuring Triangles How can the measurement of the triangle be improved? 1. Make the base larger. 2. Measure the angle more accurately.