Keeping time is a tough job. If you travel, you might cross several time zones – there are 38 of them around the world. Every year, most of us “spring forward” and “fall back” as we begin and end Daylight Saving Time. But not all time zones observe daylight time, further complicating things.

The starting point for the worldwide time system is zero degrees longitude. That line runs through Greenwich, England, which was home of the Royal Observatory. That line became the default for maps and other navigational standards.

Until the 1800s, every town and village kept its own time, based on the position of the Sun. Local noon came when the Sun crossed the meridian – the line that passes from due north to due south, crossing directly overhead.

With the birth of railroads, though, that created a mess. It was impossible to know when a train was supposed to arrive or depart. So England adopted a single time zone – Greenwich Mean Time, or GMT. That soon became the standard for defining time zones around the world.

Scientists began using GMT as a way to coordinate observations made around the world. But that was confusing. Astronomical GMT began at noon. But civil GMT – the version used for everyday life – began at midnight. So in 1935, the International Astronomical Union recommended a new name for the scientific version of GMT – Universal Time.

Universal Time is still in use today – but in several forms. More about that tomorrow.

Script by Damond Benningfield