The total apparent motion against the background sky as a result of Earth's motion halfway around its orbit of a star whose distance from the Sun is 40 pc is:

Question

Quizplus · Accepted Answer

The total apparent motion against the background sky is equal to twice the angular value of the Earth's semi-major axis divided by the distance to the star. Earth's semi-major axis is 1 AU which is approximately 1.496 x 10^11 meters. Halfway around its orbit corresponds to a distance of 0.5 AU. Therefore, the angular motion is:

2 * (0.5 * 1.496 x 10^11 meters) / (40 x 3.086 x 10^16 meters) = 0.0125 arcseconds

The Total Apparent Motion Against the Background Sky as a Result