Even after railroads adopted a standard time, however, not everyone used it in their everyday lives. Not until increased needs of transportation and communication made it advantageous, did the country move to uniform time zones. Congress passed the Standard Time Act in 1918, officially adopting the time zones established by the railroads. The responsibility of maintaining and/or changing them was first given to the Interstate Commerce Commission and later to the Department of Transportation.

It's 5 o'clock somewhere

At the Washington Meridian Conference of 1884, world leaders and scientists agreed to divide the map into 24 standard time zones, based on 15 degrees longitude and 60-minute intervals and thus accounting for each of the 24 hours in the day.

This also created the International Date Line, a zigzagging line at approximately the 180th meridian, where calendar days are separated.

So, if you are going from Salt Lake City to Tokyo, say, and leave on a Sunday morning, since you go west, the time is pushed back as you pass through time zones, but when you cross the International Date Line, it suddenly becomes Monday. Coming home, you can leave on a Monday morning and time gets later and later as you cross time zones, until you cross the International Date Line and it becomes Sunday again. Confusing? No wonder you get jet lag.

What does it mean?

The starting point for measuring modern time is Greenwich Meridian — Longitude 0 — which runs through the town of Greenwich in England, a few miles upriver from London. Every place has a latitude based on its distance from Greenwich and a time that is measured relative to Greenwich Mean Time.

The Royal Observatory in Greenwich was established by King Charles II in the mid-1600s for the purpose of "the rectifying of the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting of the art of navigation." Among the astronomers who worked there was Edmund Halley, who lent his name to the famous comet.

A ball on the roof of the observatory was erected in 1833 , and became a popular public time signal. At five minutes to 1 p.m., the ball still rises halfway up a pole, reaching the top at two minutes to 1. The ball drops at exactly 1 p.m. Because it is clearly visible to ships on the nearby Thames River, ships have used the signal to check their time.

In 1972, Universal Time replaced Greenwich Mean Time as the time reference for the scientific community. UT is taken from an atomic clock.

Does it do any good?