Time standards are now based on atomic clocks. A promising second standard is ba

Question

Time standards are now based on atomic clocks. A promising second standard is based on pulsars, which are rotating neutron stars (highly compact stars consisting only of neutrons). Some rotate at a rate that is highly stable, sending out a radio beacon that sweeps briefly across Earth once with each rotation, like a light-house beacon. Pulsar PSR 1937 + 21 is an example, it rotates once every 1.55780644887275 ± 3 ms, where the trailing ±3 indicates the uncertainty in the last decimal place (it does not mean ±3 ms). How many times does it rotate in 7.00 days?

Explanation / Answer

(a.) Find out how many ms are in one day: (24hr/1 day) x (60min/1hr) x (60s/1min) x (1000ms/1s) = 86,400,000 ms/day Divide that number by 1.557806... to get the number of rotations in one day. It equals about 5.5462 x 10^7. Multiply this by 7 to get the number of rotations in 7 days.

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