Final answer:
A time zone is supposed to be roughly 15 degrees of longitude wide to correspond with one hour of time difference. The actual boundaries of time zones can vary widely due to local decisions and practical considerations. Despite the theoretical model, countries may use less or more than the ideal number of time zones, as seen in the United States and China.
Step-by-step explanation:
A time zone is a region of the Earth that has the same standard time. Time zones follow a theoretical system that divides the world into 24 equal longitudinal zones, each being approximately 15 degrees of longitude wide. The primary purpose is to ensure that local noon corresponds with the time when the sun is at its highest point in the sky.
However, the actual boundaries of time zones can vary significantly from the ideal 15-degree width due to political, social, and geographic reasons. For instance, in the United States, time zone borders do not strictly follow lines of longitude; instead, they often follow state lines or are drawn to keep cities within a single zone. This leads to inconsistencies with the theoretical model where time zones can range from 10 to 30 degrees of longitude.
In contrast, some countries like China operate under a single time zone despite spanning multiple ideal time zones. The Chinese government has decided to use one standard time for efficiency and unity. This demonstrates how time zones, in practice, can be much wider, or narrower, than the 15 degrees of longitude that is typically associated with one hour of time change.
The concept of time zones was created during the 19th century, as a solution to the confusion caused by every city in the United States setting its own local time. With the advent of railroads and telegraph systems, a standardized time zone system became necessary for efficient operation and time coordination, hence the establishment of time zones around 15 degrees of longitude.
The total number of time zones is 24, which corresponds to the number of hours in a day, with each zone ideally intended to represent one hour difference in time. The International Date Line serves as an adjustment point for the calendar day as one travels across it.