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### How Long Would This Experiment Take?

An important consideration (since you need the answer fairly quickly in order to answer the challenge question first!) before you actually launch the probe 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. The probe must travel much slower, so the time for a light signal to travel to Cyg X-1 and back is a measure of the absolute minimum time this experiment could take. It is an easy matter to calculate this minimum time, once you know the distance to Cyg X-1.

The total distance traveled would be twice the distance to Cyg X-1.

• The distance to Cyg X-1 is 2.5 kiloparsecs.
• A kiloparsec is a thousand parsecs.
• A parsec is equal to 3.0857 x 1016m.
• The speed of light in a vacuum is 3 x 108 m/sec
 Time for light to travel to Cyg X-1 and back (rounded to the nearest 365 day year) is: years.

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