Have the students repeat parallax calculations using the data from the chart above so that they see how parallax measurement is usually used in astronomy. In actual measurements, the angles are measured on photographic plates taken at intervals along the Earth's orbit. Have the students assume the three measurements were taken each a quarter year apart, to facilitate measuring the distances between observations. For reference, 1 A.U., the distance from the Earth to the Sun, is 1.496 x 10¹¹ m and one parsec = 3.086 x 10¹⁶ m.