Accurate time

All the world lives by the “Dearth time" or the " star time" as the astronomers call it. It means that our clocks are timed according to the earth's rotation, for the turning earth is the master clock by which all other clocks are set¹.

This nightly task of timing the earth's rotation is carried out at the observatories of various countries. What an astronomer does is to determine how the star time compares with the average time of the observatory's master clocks.

To keep them as exact as possible, the clocks are protected from all outside influence. The pendulum clocks are kept underground, away from vibrations and changing temperatures Each pendulum swings in a vacuum (that is, in a case from which the air has been pumped out), for air resistance would gradually slow down their time of swing. Each pendulum swings in a different direction, too, so that the vibration of one will not affect another.

The observatories' time signals are based on crystal clocks since they are the most accurate. Vibrating crystals by means' of which these clocks are run, are sealed inside vacuum tubes and kept vibrating by electric current.

To provide the accurate telling of time an exact measure of time is required. Such a measure is the " standard second, " that is made available just as the " standard metre" and other units of measurement.

In today's world not only the second but even a fraction of a second plays an important part.

Our electric clocks are run by current that vibrates-60 times a second. If they vary from that, they are wrong.

X-ray pictures taken in one millionth of a second are now possible, to reveal what is happening inside machines operating at a very high speed.

But we are chiefly interested in the time we live by, standard time, divided into hours and minutes. An hour is a man-made thing, just one-twenty-fourth part of the time it takes for the earth to make one complete turn.

To-day the world runs on standard time, but not so long ago most localities used their own local time. In 1884 an International Meridian Conference extended standard time to the entire world which was divided into 24 time zones. Standard time in each zone varied by one hour from the next, the time at Greenwich being taken as the zero point.

In future we may use atoms to measure time, because they have within them very precise frequencies of oscillation that will prevent the clock from gaining or losing. A crystal could be adjusted to vibrate at the same rate as the atoms of some pure element.

The crystal's vibrations could be used to run a clock. Such an atom-controlled clock would keep more accurate time than the turning earth itself.

Note

1. to set a clock ‑ поставить часы по точному времени