An observer on Earth notes that an astronaut on a spaceship puts in a 4-hour shift at the controls of the spaceship. How long is this shift as measured by the astronaut himself, if the spaceship is moving with a velocity of 0.8c relative to the Earth? (See table 20.1. Be careful which observer measures the proper time?)

Table 20.1 Values of y for Different Values of Relatives Speed v v = 0.01c v = 0.1c v = 0.5c y= 1.000 05 y= 1.005 y= 1.155 v = 0.6c y= 1.250 v = 0.8c y= 1.667 v= 0.9c Y= 2.294 v= 0.99c Y= 7.088