## Time for Signal to Return

### Time for Radar Signal to Return to Earth

An important consideration (since you want to still be alive when you work for Dr. Greenglow!) is just how long it would take to complete this experiment and get the measurement you need. The light signal from the probe travels at the speed of light, which is the ultimate speed limit, but the probe must travel much slower. Also, the distances between stars is huge, so this experiment might still require a long time to complete. The the time for a light signal to travel to HT Cas and back is a measure of the absolute minimum time this experiment could take. It is an easy matter to calculate how long this approach will take, once you know the distance to HT Cas.The total distance traveled would be twice the distance to HT Cas, or 2 x 140 parsecs.

- The speed of light in a vacuum is 3 x
10
^{8}m/sec

- A parsec is equal to 3.0857 x 10
^{16}m.