Additional Problems
(a) How long does it take a radio signal to travel 150 km from a transmitter to a receiving antenna? (b) We see a full Moon by reflected sunlight. How much earlier did the light that enters our eye leave the Sun? The Earth-Moon and Earth-Sun distances are $3.8 \times 10^{5} \mathrm{km}$ and $1.5 \times 10^{8} \mathrm{km}$ , respectively. (c) What is the round-trip travel time for light between Earth and a spaceship orbiting Saturn, $1.3 \times 10^{9} \mathrm{km}$ distant? (d) The Crab nebula, which is about 6500 light-years (ly) distant, is thought to be the result of a supernova explosion recorded by Chinese astronomers in A.D. 1054. In approximately what year did the explosion actually occur? (When we look into the night sky, we are effectively looking back in time.)