At this time tomorrow, New Horizons will have had made its closest fly-by of the dwarf planet Pluto. An interesting thing to note is that New Horizons is 31.89 AU from the Earth! One AU is basically the measure of the average distance of the Earth from the sun, i.e., approximately 1.5*10^11 meters. Light travels at 3*10^8 m/s. Communication with the spacecraft, which takes place at the speed of light, takes some time, even though the speed of light is so fast! This just shows us that space is a big place.
Signals to and from New Horizons would take:
time for signals to be sent and received = 2*31.89*1.5*10^11 m/3*10^8 m/s
or, t= 31.89*10^3 seconds
or, t= 31.89*10^3/3600 hours
time for a signal to be sent and received= 8.85 hours = 8 hours 51 minutes
So, even at the fastest speed possible, a message sent to New Horizons and it replying at the instant the message was received, it would take the message a whopping 8 hours 51 minutes after the original message was sent, to be received.
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