The concept of having a time zone comes from a basic desire to always have the local time correspond to the amount of daylight that is available. Most people tend to think of the middle of the day, or high noon, as being the time at which the sun is at the highest point in the sky. Obviously, the perception of this state would be different at various points around the world, and the sun would appear to be at its highest point at a different time of day in Europe than it would appear to be front and center in the United States. Setting time zones helps to accommodate this desire.
Time zones are configured based on using an agreed upon starting point, known as the prime meridian. It has been referred to as Greenwich Mean Time, universal time, or Greenwich Meridian time. Since GMT is point zero for calculating times, all time zones are understood as being a certain number of hours ahead or behind this universal time. Taking this as the basic standard, the zones established in 15° slices all around the world. The use of 15° as an acceptable standard was first developed in the late 19th century, and remains the basis for the 24 divisions that currently exist around the world.
An interesting fact is that, while the starting point for fixing the arrangement of time zones remains the same, the actual facility that once resided at the median time location is no longer there. During the 1950s, the famed Greenwich observatory, the starting place for the concept, was moved to Sussex, England. The original site is still considered to be the prime meridian.
While some time zones do experience a slight shift in the spring and autumn of the year, their process and function remains the same. In a world where interaction with distant locations has become a daily occurrence, that function has become even more important to establishing communications for both business and pleasure.