Final answer:
The continental United States and parts of Canada are divided into four main time zones: Eastern, Central, Mountain, and Pacific, with separate zones for Alaska and Hawaii resulting in a total of six. These zones were established to standardize time across different regions due to the necessity brought about by travel and communications advancements.
Step-by-step explanation:
The continental United States and parts of Canada are divided into four main time zones based on their location: Eastern, Central, Mountain, and Pacific. In addition, there are separate time zones for Alaska and Hawaii, making a total of six time zones for the United States. These time zones exist because the Earth rotates once every 24 hours at a rate of 15 degrees per hour, with time zones established roughly every 15 degrees of longitude to correspond with local hours of day and night. While the concept of having time zones that follow 15-degree longitude lines is straightforward, their practical implementation often considers state, regional, or local boundaries, which can make them less uniform.
In the past, every city and town had its own local time, but the development of the railroad and telegraph systems necessitated a standardization of time. By 1883, the U.S. adopted its initial time zones. These zones are designed to help organize the ways in which time is kept across different regions, maintaining a synchronized standard that is crucial for transport, communication, and business. This system now means that for most parts of the world, including the United States and Canada, travelers only need to change their watches when they move across zones that result in a full one-hour difference.