1) Close 1 eye, hold thumb up to moon 2) Adjust distance of thumb from face until it just barely occludes vision of the moon. 3) Holding very still, use accur

1) Close 1 eye, hold thumb up to moon 2) Adjust distance of thumb from face until it just barely occludes vision of the moon. 3) Holding very still, use accurate calipers to measure thumb. Under many repetitions with many different experimenters, this should consistently yield a result showing that the width of the moon is one thumb wide.