Astronomers are always making comparisons between measurements in astronomy and something that might be more familiar. for example, the hipparcos web pages tell us that the measurement accuracy of 0.001 arcsec is equivalent to the angle made by a golf ball viewed from across the atlantic ocean, or to the angle made by the height of a person on the moon as viewed from earth, or to the length of growth of a human hair in 10 sec as seen from 10 meters away. use the ideas in example 19.2 to verify one of the first two comparisons.