Answer
500 s, which is about 8.3 min.
1000 s, which is less than Ole Roemer's determination of 1300 s.
Work Step by Step
If c denotes the speed of light, then $d = 1.5 \times 10^{11} m = ct$. Solve for t = d/c.
$$\frac{1.5 \times 10^{11} m }{300,000,000 m/s} = 500 s$$
The time for light to cross the diameter of the Earth’s orbit is twice that number, or 1000 s. Ole Roemer got reasonably close (question 33).
