Are you a time pedant? When I was a kid, I used to ring 1194 and set my watch and every clock in the house to the telephone talking time. It didn't mean I was early to everything - I just knew precisely how late I was!
So how important is knowing the exact time? Surely within a few seconds is more than good enough.
We do have some technology we use regularly where high levels of time accuracy are absolutely vital - and scientists are working on ways to improve that accuracy.
GPS has changed our lives since it became operational in 1993. The US launched 32 satellites from 1978 at a height of 20,180km above the Earth. With 24 of those satellites active at any given time, they rotate around the earth twice a day such that you should be able to "see" at least four satellites from most places on earth.
The simple GPS then relies on some incredibly accurate timekeeping to determine your position. Each satellite knows the precise time - to within 14 nanoseconds. The information that is continually transmitted by each satellite down to earth contains the satellite position and the time. By comparing the known time with how long it took for the message to be received and using a process called trilateration, receiving data from a minimum of four satellites is enough to locate your position. If the clocks are aligned.
Radio waves are a form of electromagnetic radiation and therefore travel at the speed of light. Approximately 2.998 x 100,000,000 metres per second. In 14 nanoseconds, a radio wave can travel 4.2 metres.
The satellites carry very stable atomic clocks. Despite their accuracy, they still may drift by a few nanoseconds, keeping in mind that each nanosecond represents 30 centimetres. To prevent this drift having any significant consequences, GPS satellites synchronise their time with each other and the ground twice a day.
As we increase the number of objects we are sending away from our planet, how do we navigate as we head to the moon or Mars or beyond. It would seem with pretty much the same method. The difference is that the distant object takes somewhat longer to receive the signal and time delay starts to make updating the clock problematic. A more accurate onboard clock is needed.
Early atomic clocks had accuracies in the vicinity of one second per 100 years. When you consider it might take a spacecraft seven months to reach Mars, that level of accuracy may mean you miss your landing spot by 1800 kilometres.
Voyager 1, launched in 1977, is currently 23 million kilometres from earth. Without updates, this level of accuracy could see a spacecraft 132,000km offline.
Luckily science has an answer.
Build more accurate atomic space clocks. The most accurate atomic clocks are here on the ground, about the size of a refrigerator and their accuracy is measured by stability of one second per several billion years. Everything that goes in to space needs to use less energy, be smaller and weigh less while being more robust.
To that end, NASA's Deep Space Atomic Clock (DSAC) project reports that they are at the level of a toaster sized clock achieving stability of one second per 14 million years. Not bad.
Next time the clock on your microwave oven is out by a minute, shake your fist at it and tell it that time is more accurate up in space.
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