Accuracy of the time | ||||
Measurement of time | Automatic translation | Updated May 16, 2015 |
Historically, humans measure time passing. The rotation of the Earth allowed him to divide the time in days between two sunrises or sunsets. Today the movements of the Earth are constantly monitored using techniques more and more advanced. With sundials day was divided into hours, and the clocks were divided in hours minutes and seconds. But it is not enough to avoid the drifts of the time, scientists have found mechanisms more and more accurate to measure the time. The vibration of the quartz crystal has helped improve the time precision to thousandth of a second but it was not yet accurate enough for technological research demand more and more precision. So we used the natural frequency of certain atoms and in particular the isotope cesium-133 atom whose oscillations emit pulses of light. The oscillation frequency of the cesium atom is incredibly high, that is what scientists seeking for a high frequency allows time measurement with high accuracy. This is the cesium atom which currently guarantees the correctness of the time on our planet. If we bombards with energy the cesium atom, using a laser, it vibrates emitting light pulses at a frequency of 9,192,631,770 Hz. With the frequency of 9,192,631,770 light pulses per second, the precision is such that the clock loses or gains a second, that every 100 million years. | Image: The rotational speed of the Earth at the equator is 1 674.364 km / h. The number of rotations of the Earth itself is about 365,2425 per year, 365.2425 days sidereal (rotation relative to the celestial reference system). However, all the movements of the earth are irregular and vary gradually over time. Moon with tidal effects slows the rotation of the Earth itself. Day length on Earth slowly increasing by about 2 milliseconds per century. Thus 300 million years ago, years lasted 400 days, meaning that days were 22 hours long. When the Earth formed, 4.5 billion years ago, years lasted 1434 days meaning that days were 6.1 hours long. | |
Clocks increasingly accurate | ||
Table: accuracy of the time measurement, in seconds, on one day, through the centuries. |